We divide the recent Pleurodira into three families, of which that of

_Carettochelys_ stands apart by its paddle-shaped limbs and the absence of

horny shields. The Pelomedusidae and Chelydidae are closely allied. The

former are not Australian, and are externally distinguished by the absence

of a nuchal shield.

FAM. 1. PELOMEDUSIDAE.–Neck completely retractile within the shell.

Carapace without a nuchal shield. The plastron is composed of eleven

plates, there being besides the unpaired endo-plastron a pair of

meso-plastra, situated between the hyo- and hypo-plastra; but these

meso-plastra meet in the middle line in _Sternothaerus_ only, while in

_Podocnemis_ and _Pelomedusa_ they are restricted to small pieces on the

bridge, widely separated from each other by the usual hyo- and

hypo-plastral suture. A nuchal shield is absent; there are twenty-four

marginal and thirteen plastral shields, inclusive of the conspicuous

intergular. The temporal fossa is widely open, except in _Podocnemis_,

where it is partly roofed in by the meeting of the much-expanded

quadrato-jugal with the parietal. The palatine bones are in median contact,

not separated by the vomer. Nasal bones being absent, the large prefrontals

meet in the middle line. The second cervical vertebra is biconvex.

This family is now represented by only three genera, with about fifteen

species in Africa, Madagascar, and South America.

_Sternothaerus._–Skull without a bony supratemporal roof. Meso-plastra

large, extending right across the plastron. Anterior lobe of the plastron

movable, the hinge passing between the hyo- and meso-plastral plates, and

between the pectoral and abdominal shields. Fore- and hind-limbs with five

short digits and claws. Several species in tropical and southern Africa,

and {391}in Madagascar. _S. derbianus_ in West Africa, from the Gambia to

Angola, is the largest species, with a shell nearly one foot in length.

_Pelomedusa._–Skull with a slender parieto-squamosal arch. Meso-plastra

small and lateral. Plastron without a hinge. Fore- and hind-limbs with five

very short digits and five claws. Top of the head with one pair of shields

between the eyes, and with a large interparietal and a pair of parietals

behind.

_P. galeata_, the only species, occurs in Madagascar and nearly the whole

of Africa south of the Sahara, from the Cape to Abyssinia, and in the

Sinaitic peninsula. The shell, less than one foot in length, is much

depressed and is obtusely keeled; brown above with black spots;

brownish-yellow below. The short and broad head is coloured like the rest,

without ornamentation. In Somaliland this species sleeps hidden on land

during the dry seasons, from July to the end of September, and from January

to March, and appears at once after the rains have set in.

_Podocnemis._–With a supratemporal roof formed by the junction of the

parietal with the quadrato-jugal. Meso-plastra small and lateral. Fore- and

hind-limbs broadly webbed, with five and four claws respectively. The

fore-arms and the outer edges of the hind-feet with several conspicuous

shields, hence the generic name. Head with an interparietal, two parietals,

and a narrow unpaired shield between the eyes. The tail is very short. The

carapace is flat and broad, strongly serrated on the posterior margin. Chin

with one or two short barbels. Several species in South America, chiefly in

the basin of the Amazon, and one in Madagascar.

_P. expansa._–Very common in Tropical South America, east of the Andes. The

female, which is much larger than the male, has a shell nearly three feet

in length. Olive-brown above with darker patches; yellowish below. With a

few yellow spots above and behind the eyes, and on the parietal region. The

"Arrau" turtle is of great commercial importance on account of the eggs,

which are periodically collected in enormous quantities, chiefly for the

oil. This is either eaten, like the eggs themselves, or used for burning in

lamps, or as an addition to tar. The turtles are likewise eaten by man and

beast. Thousands of the little creatures are snapped up by Jabiru storks,

alligators, and fishes; the adults fall an easy prey {392}to the prowling

jaguar, which turns them over on to their backs and neatly cleans out the

flesh with its sharp and powerful claws.

Fertilisation takes place in the water, the eggs are deposited on land, in

sand-banks, the female digging a hole about two feet deep and covering up

the numerous soft-shelled eggs with sand. The time of deposition is the

early hours of the morning, but the season depends upon the beginning of

the principal rains, since the young are hatched shortly before the

torrential rains. This season differs considerably in the various

countries. The hatching takes about forty days; the eggs are consequently

laid in the Amazon countries during the months of September to November, in

the Orinoco district in March. This species lives in the pools of the

inundated forests, and when these are dried up, the animals retire into the

rivers themselves. Their food consists mainly of the fruit dropping down

from the trees.

Bates, in his delightful book, _The Naturalist on the River Amazon_, gives

the following lively and exhaustive account of his experience with these

turtles:–

"I accompanied Cardozo in many wanderings on the Solimoes, during which we

visited the 'praias' (sand islands), the turtle pools in the forests, and

the by-streams and lakes of the great desert river. His object was mainly

to superintend the business of digging up turtle eggs on the sandbanks,

having been elected commandant for the year by the municipal council of

Ega, of the 'praia real' of Shimuni, the one lying nearest to Ega. There

are four of these royal praias within the Ega district, a distance of 150

miles from the town, all of which are visited annually by the Ega people

for the purpose of collecting eggs and extracting oil from their yolks.

Each has its commander, whose business is to make arrangements for securing

to every inhabitant an equal chance in the egg harvest, by placing

sentinels to protect the turtles whilst laying, and so forth. The pregnant

turtles descend from the interior pools to the main river in July and

August, before the outlets dry up, and there seek in countless swarms their

favourite sand-islands; for it is only a few praias that are selected by

them out of the great number existing. The young animals remain in the

pools throughout the dry season. These breeding places of turtles then lie

20 to 30 or more feet above the level of the river, {393}and are accessible

only by cutting roads through the dense forest....

"We found the two sentinels lodged in a corner of the praia, where it

commences at the foot of the towering forest-wall of the island, having

built for themselves a little rancho with poles and palm-leaves. Great

precautions are obliged to be taken to avoid disturbing the sensitive

turtles, who, previous to crawling ashore to lay, assemble in great shoals

off the sand-bank. The men, during this time, take care not to show

themselves, and warn off any fisherman who wishes to pass near the

place....

"I rose from my hammock by daylight, shivering with cold; a praia, on

account of the great radiation of heat in the night from the sand, being

towards the dawn the coldest place that can be found in this climate.

Cardozo and the men were already up watching the turtles. The sentinels had

erected for this purpose a stage about fifty feet high, on a tall tree near

their station, the ascent to which was by a roughly made ladder of woody

lianas. They are enabled, by observing the turtles from their watch-tower,

to ascertain the date of successive deposits of eggs, and thus guide the

commandant in fixing the time for the general invitation to the Ega people.

"The turtles lay their eggs by night, leaving the water, when nothing

disturbs them, in vast crowds, and crawling to the central and highest part

of the praia. These places are, of course, the last to go under water when,

in unusually wet seasons, the river rises before the eggs are hatched by

the heat of the sand.... The hours between midnight and dawn are the

busiest. The turtles excavate with their broad webbed paws deep holes in

the fine sand; the first-comer, in each case, making a pit about three feet

deep, laying its eggs (about 120 in number), and covering them with sand;

the next making its deposit at the top of that of its predecessor, and so

on until every pit is full. The whole body of turtles frequenting a praia

does not finish laying in less than fourteen or fifteen days, even when

there is no interruption. When all have done, the area (called by the

Brazilians 'taboleiro') over which they have excavated is distinguishable

from the rest of the praia only by signs of the sand having been a little

disturbed.

"I mounted the sentinel's stage just in time to see the turtles retreating

to the water on the opposite side of the sand-bank, {394}after having laid

their eggs. The sight was well worth the trouble of ascending the shaky

ladder. They were about a mile off, but the surface of the sands was

blackened with the multitudes which were waddling towards the river; the

margin of the praia was rather steep, and they all seemed to tumble head

first down the declivity into the water.... Placards were posted up on the

church doors at Ega, announcing that the excavation on Shimuni would

commence on the 17th of October, and on Catuá, sixty miles below Shimuni,

on the 25th. By the morning of the 17th some 400 persons were assembled on

the borders of the sand-bank, each family having erected a rude temporary

shed of poles and palm-leaves to protect themselves from the sun and rain.

Large copper kettles to prepare the oil, and hundreds of red earthenware

jars, were scattered about on the sand.

"The excavation of the taboleiro, collecting the eggs, and purifying the

oil, occupied four days. All was done on a system established by the old

Portuguese governors, probably more than a century ago. The commandant

first took down the names of all the masters of households, with the number

of persons each intended to employ in digging; he then exacted a payment of

140 reis (about 4d.) a head towards defraying the expense of sentinels. The

whole were then allowed to go to the taboleiro. They ranged themselves

round the circle, each person armed with a paddle, to be used as a spade,

and then all began simultaneously to dig on a signal being given–the roll

of drums–by order of the commandant. It was an animating sight to behold

the wide circle of rival diggers throwing up clouds of sand in their

energetic labours, and working gradually towards the centre of the ring. A

little rest was taken during the great heat of mid-day, and in the evening

the eggs were carried to the huts in baskets. By the end of the second day

the taboleiro was exhausted; large mounds of eggs, some of them four to

five feet in height, were then seen by the side of each hut, the produce of

the labour of the family.

"In the hurry of digging, some of the deeper nests are passed over; to find

these out, the people go about provided with a long steel or wooden probe,

the presence of the eggs being discoverable by the ease with which the spit

enters the sand. When no more eggs are to be found, the mashing process

begins. {395}The egg, it may be here mentioned, has a flexible or leathery

shell; it is quite round, and somewhat larger than a hen's egg. The whole

heap is thrown into an empty canoe and mashed with wooden prongs; but

sometimes naked Indians and children jump into the mass and tread it down,

besmearing themselves with yolk, and making about as filthy a scene as can

well be imagined. This being finished, water is poured into the canoe, and

the fatty mass is then left for a few hours to be heated by the sun, on

which the oil separates and rises to the surface. The floating oil is

afterwards skimmed off with long spoons, made by tying large mussel-shells

to the end of rods, and purified over the fire in copper kettles.

"The destruction of turtle eggs every year by these proceedings is

enormous. At least 6000 jars, holding each three gallons of the oil, are

exported annually from the Upper Amazons and the Madeira to Para, where it

is used for lighting, frying fish, and other purposes. It may be fairly

estimated that 2000 more jarfuls are consumed by the inhabitants of the

villages on the river. Now, it takes twelve basketfuls of eggs, or about

6000, by the wasteful process followed, to make one jar of oil. The total

number of eggs annually destroyed amounts, therefore, to 48 millions. As

each turtle lays about 120, it follows that the yearly offspring of 400,000

turtles is thus annihilated. A vast number, nevertheless, remain

undetected; and these would probably be sufficient to keep the turtle

population of these rivers up to the mark, if the people did not follow the

wasteful practice of lying in wait for the newly-hatched young, and

collecting them by thousands for eating; their tender flesh, and the

remains of yolk in their entrails, being considered a great delicacy. The

chief natural enemies of the turtle are vultures and alligators, which

devour the newly-hatched young as they descend in shoals to the water.

These must have destroyed an immensely greater number before the European

settlers began to appropriate the eggs than they do now. It is almost

doubtful if this natural persecution did not act as effectively in checking

the increase of the turtle as the artificial destruction now does. If we

are to believe the tradition of the Indians, however, it had not this

result; for they say that formerly the waters teemed as thickly with

turtles as the air does now with mosquitoes. The universal {396}opinion of

the settlers on the Upper Amazon is, that the turtle has very greatly

decreased in numbers, and is still annually decreasing.

"The principal object of another expedition was to search certain pools in

the forest for young turtle. We started from the praia at sunrise on the

7th of October in two canoes, containing twenty-three persons, nineteen of

whom were Indians. The pool covered an area of about four or five acres,

and was closely hemmed in by the forest, which, in picturesque variety and

grouping of trees and foliage, exceeded almost everything I had yet

witnessed. The margins for some distance were swampy, and covered with

large tufts of fine grass. The pool was nowhere more than five feet deep,

one foot of which was not water, but extremely fine and soft mud.

"Cardozo and I spent an hour paddling about. The Indians seemed to think

that netting the animals, as Cardozo proposed doing, was not lawful sport,

and wished first to have an hour or two's old-fashioned practice with their

weapons. I was astonished at the skill which they displayed in shooting

turtles from little stages made of poles and cross pieces of wood. They did

not wait for their coming to the surface to breathe, but watched for the

slight movements in the water which revealed their presence underneath.

These little tracts on the water are called the siriré; the instant one was

perceived an arrow flew from the bow of the nearest man, and never failed

to pierce the shell of the submerged animal. When the turtle was very

distant, of course the aim had to be taken at a considerable elevation, but

the marksmen preferred a longish range, because the arrow then fell more

perpendicularly on the shell, and entered it more deeply.

"The arrow used in turtle-shooting has a strong lancet-shaped steel point

fitted into a peg, which enters the tip of the shaft. The peg is secured to

the shaft by twine, being some thirty or forty yards in length, and neatly

wound round the body of the arrow. When the missile enters the shell the

peg drops out, and the pierced animal descends with it towards the bottom,

leaving the shaft floating on the surface. This being done the sportsman

paddles in his canoe to the place, and gently draws the animal by the

twine, humouring it by giving it the rein when it plunges, until it is

brought again near the surface, when {397}he strikes it with a second

arrow. With the increased hold given by the two cords he has then no

difficulty in landing his game.

"By mid-day the men had shot about a score of nearly full-grown turtles.

Cardozo then gave orders to spread the net.... Three boat loads, or about

eighty, were secured in about twenty minutes. They were then taken ashore

and each one secured by the men tying the legs with thongs of bast.

"When the canoes had been twice filled we desisted after a very hard day's

work. Nearly all the animals were young ones, chiefly, according to the

statement of Pedro, from three to ten years of age; they varied from 6 to

18 inches in length, and were very fat. Cardozo and I lived almost

exclusively on them for several months afterwards. Roasted in the shell

they form a most appetising dish. These younger turtles never migrate with

their elders on the sinking of the waters, but remain in the tepid pools,

fattening on fallen fruits, and, according to the natives, on the fine

nutritious mud. We captured a few full-grown mother turtles, which were

known at once by the horny skin of their breast plates being worn, telling

of their having crawled on the sand to lay eggs the previous year. They had

evidently made a mistake in not leaving the pool at the proper time, for

they were full of eggs, which, we were told, they would, before the season

was over, scatter in despair over the swamp. We also found several male

turtles, or capitaris, as they are called by the natives. These are

immensely less numerous than the females, and are distinguishable by their

much smaller size, more circular shape, and the greater length and

thickness of their tails. Their flesh is considered unwholesome, especially

to sick people having external signs of inflammation."

The most recent account of these water tortoises is that published by Dr.

Goeldi from the MS. of João Martins da Silva Continho, a former resident at

Manáos on the Middle Amazon. The "Tartaruga" (the Portuguese name for

turtles) live from January to July in the inundated, quiet backwaters of

the forest-region, feeding upon the various seeds of palms as these ripen

and drop successively; rarely, and only when hard up, they are carnivorous.

The creatures hide under water below the trees, when they are espied by the

Indians, who dive down to a depth of twenty and more feet to catch them in

their arms. The {398}civilised Indians use a steel-pointed lance of hard

wood, about 10 feet in length. A string connects the point with the shaft

around which it is wound. When stuck into the tortoise the shaft and point

part; the string is either tied to the boat or to a little float of light

wood. In other districts an arrow with a string is employed.

In August, when the water subsides, the tortoises return to the rivers, and

the entrance of the lagoon is closed with nets. A number of boats with long

poles drive them with much noise towards the entrance. On their way to the

rivers the tortoises always go up-stream, and this is called the "arribaçaõ

das tartarugas," the ascent of the turtles. The fishermen post themselves

at shallow spots or on sand-banks, and wait for the creatures which come up

to find a place for landing and laying. The arrows employed are called

_sararaca_, _i.e._ a thing which can be disjointed; they are about 4 feet

long, and consist of a _gomo_ or internodium of wood 9 inches long with a

one- or two-barbed steel point, and the shaft into which the _gomo_ fits

loosely. The _gomo_ is, moreover, connected with the shaft by a string made

of palm-fibres about 30 feet in length, partly wound round the shaft, which

ultimately acts as a float.

The laying takes place from the end of September into October. Some of the

parents seem to reconnoitre on land for a few days. As a rule only females

do this, and the natives say that they are led by a "_mestra_." The laying

takes place early in the morning. The number of females is so great that

they often block the way of the boats, and make a great noise by knocking

against their neighbours' shells. Each digs a hole about 18 inches or 2

feet deep, and lays from 80 to 200 eggs. Sometimes the laying individual is

entirely buried by its neighbours which are scraping their own holes.

In some districts the eggs are wanted for "manteiga" (Portuguese for

butter); and the turning over, or _viraçaõ_ of the tortoises takes place

later. In other districts they are caught before the eggs are laid, and

this barbaric and destructive custom was formerly forbidden by the people

themselves. Although the provincial assembly tried to reinstitute the old

reasonable customs, the inspectors are often got over by bribery.

There are two ways of extracting the oil from the eggs. To get the thick

oil used, mixed with tar, for shipbuilding, caulking, {399}etc., the eggs

are heaped up for five days and then worked. The fluid oil for lighting is

made from fresh eggs, which are put into a boat and then trampled out with

the feet. The oil is drawn off into large earthen jars and put on the fire.

Then it is rapidly cooled. The best oil, used for frying fish, is that

which is gained from the roasted tortoises themselves. Fresh eggs are

either fried or taken with sugar, or mixed with manioca-flour and water.

The young, which are hatched in January, are likewise eaten fried, or they

are preserved in the fat of the parents.

An average tortoise yields 5 lbs. of fat, costing on the spot two milreis.

The whole full-grown animal, of one yard in length, costs the same, and its

meat is sufficient to sustain a family of six people for three days. To

make 24 lbs. of oil requires 3000 eggs. Two or three tortoises would yield

the same amount from their fat. Consequently the destruction of the eggs

causes an enormous waste, and is after all the least economical procedure.

In the year 1719, 192,000 lbs. were exported from the Alto Amazonas,

representing 24,000,000 eggs. In 1700 there were still plenty of tortoises

50 leagues above the mouth of the Para river. Now there is no assembly of

more than fifteen tortoises to be found anywhere within 300 leagues from

Para to the mouth of the Rio Negro. On the Rio Madeira, from the mouth to

the first cataract, 186 leagues distance, there are now only two regular

nesting localities. The upper Solimoes and the Rio Yapura are still rich.

Near Ega are regular tortoise-ponds, called "curral," which yield

sufficient support to their owners; the animals are fed with manioca-flour

and leguminous plants.

FAM. 2. CHELYDIDAE.–The neck bends under the margin of the carapace, but

remains partly exposed. The nuchal shield is absent except in two Northern

Australian species. There are twelve pairs of marginal shields. The

plastron is composed of nine plates, and is covered with thirteen shields,

one of which is the conspicuous intergular. The temporal region of the

skull shows great diversity. It is quite open in _Chelodina_, covered in by

broad expansions of the parietal bones in _Platemys_, _Emydura_, and

_Elseya_, or bridged over by a parieto-squamosal arch, which is very

slender in _Rhinemys_, strong in _Chelys_ and _Hydraspis_. The palatine

bones are separated by the vomer; the nasals are variable, mostly present,

but the prefrontals are always small, and separated {400}by the frontals.

The fifth and eighth cervical vertebrae are biconvex.

This family, still represented by nearly thirty species, which are divided

into eight genera, is restricted to Notogaea, namely, South America and

Australia.

[Illustration: FIG. 87.–Skull of _Chelys fimbriata_. × 1. A, Dorsal view of

skull; B, side view of skull and hyoid apparatus. _Cop_, copular piece;

_F_, frontal; _J_, jugal; _L.o_, lateral occipital; _Mand_, mandible; _Op_,

opisthotic; _Orb_, orbit; _Par_, parietal; _Pt.f_, postfrontal; _Ptg_,

pterygoid; _Q_, quadrate; _Qj_, Quadrato-jugal; _Sq_, squamosal; I, II,

First and second branchial arch.]

_Chelys fimbriata_, the "Matamata," the only species of this genus,

inhabits the rivers of Guiana and Northern Brazil. Besides the nuchal,

there are seven neural plates; the last pair of costals form a median

suture. Nasal bones are absent. The jaws are very weak. The Matamata has a

very peculiar appearance. The nose is produced into a long, soft tube, at

the end of which open the tiny nostrils. The eyes are very small, and the

orbits are placed very near the anterior end of the skull, while the

parietal {401}region is broad and much elongated (Fig. 87, p. 400). The

quadrates are drawn out into trumpet-shaped tubes. The hyoid apparatus is

very large, with enormous anterior and posterior horns. The head and neck

are as long as or even longer than the carapace, which is covered with

thick, lumpy shields. The skin of the thick neck, of the sides and under

parts of the head, is produced into many soft arborescent excrescences or

fimbriae, those of the chin and throat and the large ear-flaps being

movable at will, and probably used to attract fishes and other prey. The

tail is very short. The fore- and hind-limbs are webbed, the former with

five, the latter with four claws. Old specimens, which reach a total length

of three feet, are uniformly dark brown, and look like a log covered with

rough bark. The young are far less ugly, with black and yellow spots on the

shell, and with dark stripes along the neck.

[Illustration: FIG. 88.–_Chelys fimbriata_ ("Matamata"). × ⅒.]

Very little is known about the habits of this peculiar creature. It is said

to lie submerged in the water, waiting for fishes, frogs, or tadpoles,

which are attracted by the playing motions of its cutaneous excrescences.

The jaws being so weak, and being covered with a partly soft lip-like skin,

it is probable that they are not used for seizing the prey, but that the

latter is engulfed into the mouth with the inrush of water into the throat.

{402}That this can be widened enormously is indicated by the greatly

developed hyoid apparatus.

_Chelodina._–The neck is long and slender, the head small and smooth. The

nuchal is terminal; the intergular is large. The neural plates are

completely suppressed, all the eight pairs of costal plates meeting in the

middle line. The shell is very flat. Anterior and posterior limbs entirely

webbed, and with only four claws. The tail is very short. Three species in

Australia, one in New Guinea.

[Illustration: FIG. 89.–_Chelodina longicollis._ × ⅓.]

_Ch. longicollis_ reaches a shell-length of ten inches. It inhabits

Southern Australia. The illustrations make a detailed description

unnecessary. The colour of the dorsal shield is uniformly dark rich brown,

while the shields of the under surface are yellow, with broad dark brown

lines along the sutures. These "long-necked Chelodines" have a striking

appearance, when they swim or creep about, with the neck either stretched

out straight or bent horizontally in an S-shape. The whole creature looks

neat and elegant; the iris is pale yellow, and gives the eye a very

intelligent expression. They keep well in captivity, provided they are

given the choice of land and water. My own prefer to spend most of the day

on land, preferably under the ledge of a stone, or perched upon the stone

itself if the latter is in the shade, and not too much exposed to view.

There they lie motionless, with the neck neatly tucked under the shell,

either to the right or to the left. Although the eyelids may be closed,

they can see well enough, owing to the transparent condition of the lower

lid. They feed in the water upon soft animals, as for instance worms,

smooth caterpillars, cockroaches or little frogs; and they also take meat

readily, provided this is moved about. The food is invariably taken with a

quick sideward jerk of the neck and head.

{403}[Illustration: FIG. 90.–_Chelodina longicollis_ (Australian

long-necked Chelodines). × ¼.]

My specimens soon became so tame that they left the water, and ran up to me

with the necks stretched to their full length, then snatching the bit of

food, and retiring into the pond to swallow it. When left to themselves

they are rather nocturnal in their feeding habits. Now and then they tuck

themselves away for weeks without feeding, for instance when they go

through a regular term of {404}aestivation in the summer. The last winter

they spent buried in the moss, but occasionally, especially on bright and

sunny days, they went into the water for a few hours, chiefly to drink, but

sometimes also to take a little food.

_Hydromedusa_, a South American genus, has a neck even longer than that of

_Chelodina_, which it much resembles externally. But the nuchal shield,

large and broad transversely, is situated behind the anterior marginals,

looking therefore like a sixth neural shield. The neural plates form a

continuous row, only the last pair of costal plates meeting in the middle

line. _H. tectifera_ occurs in Southern Brazil, and in the La Plata. The

shell is dark brown above; yellowish, with dark spots, below; the head and

neck are olive-coloured, adorned with a broad white, black-edged band on

either side. Fore- and hind-limbs broadly webbed, and with four claws.

Total length of the shell about eight inches.

FAM. 3. CARETTOCHELYDIDAE.–The shell is covered with soft skin instead of

horny shields. The limbs are transformed into paddles, with elongated

digits, and have only two claws. The neck is short, and not retractile. In

other respects the skeleton, notably the plastron, pelvis, and skull,

conform with the Pleurodirous type. Only one species, _Carettochelys

insculpta_, still imperfectly known, from the Fly River, New Guinea. Length

of the shell of the only complete specimen about 18 inches. This peculiar

creature seems to stand in the same relation to the typical Pleurodira, as

do the Chelonidae to the Testudinidae, except for the complete reduction of

the horny shields upon the shell, recalling in this respect _Sphargis_ and

_Trionyx_.

SUB-ORDER 3. TRIONYCHOIDEA.–The shell is very flat, oval, or almost round,

and is covered with soft, leathery skin instead of with horny shields. The

limbs are broadly webbed, and only the three inner digits are provided with

claws. Carnivorous, found in the rivers of Asia, Africa, and North America.

The head and neck are completely retractile, bending by a sigmoid curve in

a vertical plane like that of the Cryptodira. The jaws are concealed by

soft, lip-like flaps, and the nose forms a soft short proboscis. The ear is

hidden. The skull, Fig. 91, is flat, with three long posterior processes,

formed by the supra-occipital above, and the squamosals on either side. The

whole temporal region forms a wide, shallow fossa, without any

{405}indication of being arched or bridged over. The premaxilla is

extremely small, unpaired, not even reaching the nasal cavity or the vomer.

The maxillaries are correspondingly enlarged, surrounding the choanae,

which are separated by the narrow vomer. The palatines form a median

suture, and are joined behind by the long basisphenoid, which separates the

long pterygoids from each other. The quadrate is trumpet-shaped, with a

posterior notch for the stapes. The zygomatic arch is complete, and is

formed by the quadrato-jugal and the jugal; the latter joins the maxillary

and postfrontal, mostly reaching the orbit; in some cases it also just

meets the parietal, thereby adding to the strength of the postorbital arch.

The prefrontals are large; nasals are absent. The mandible is remarkable

for the great development of the coronoid process.

[Illustration: FIG. 91.–Skull of _Trionyx hurum_. _A_, From above; _B_,

from the left side; _Cond_, occipital condyle; _Fr_, frontal; _J_, _Jug_,

jugal; _L.o_, lateral occipital; _Max_, maxillary; _Op.o_, opisthotic;

_Par_, parietal; _Pr.f_, prefrontal; _Pro_, prootic; _Pt.f_, postfrontal;

_Q_, quadrate; _Qj_, quadrato-jugal; _S.o_, supra-occipital; _Sq_,

squamosal.]

The pubic and ischiadic bones enclose a large heart-shaped foramen, and are

free from the plastron; the ilia are attached only to the sacral ribs. The

carapace is peculiar in so far as it is very incomplete peripherally, the

ribs extending considerably beyond the costal plates, nor are they joined

by marginal plates, which are absent, unless they are represented by a few

small ossifications imbedded in the posterior marginal flap of the disc

(_Emyda_ of India). The rim of the disc is always formed by a horizontal,

cutaneous, very flexible flap. All the dorsal plates have a rough upper

surface, vermiculated or rugose, as usual with such dermal bones, which

have lost most of or all their horny covering, and have sunk more deeply

into the skin. The {406}nuchal plate has usually a pair of rib-like

processes. The neurals form a continuous series, except in the African

_Cyclanorbis_, in which they are much reduced in size, and separated by the

costal plates.

The plastron is imperfect, all its constituent nine elements being only

loosely connected with each other, and there remains a wide median vacuity

between the lateral elements. Most of these plastral bones are reduced to

splints, which, instead of meeting by regular sutures, loosely

interdigitate with their jagged edges. In the young all these ventral

elements are deeply imbedded in the soft, leathery skin, and they do not at

all resemble in appearance those of the dorsal side. With age they develop

upon their ventral surface stronger and denser ossifications, which

ultimately broaden out, sometimes beyond the original underlying bone, and

assume the characteristic vermiculated surface-appearance. This is

undoubtedly a process of exostosis, a step towards revival of that armour

which had been much reduced ancestrally. To appreciate this condition, it

is at least suggestive that these mud-tortoises, when kept in the usual

hard-bottomed tanks, invariably become sore, the skin wearing through where

the imbedded plastral bones touch the ground. Thus what is crammed into the

short life of a captive individual, is in the natural course of events

spread over many generations, whereby it has ceased to be pathological, and

has become a comparatively new, tertiary, but regular feature.

It is not open to much doubt that the characteristic features of the

Trionychoidea are not primitive but secondary. This is indicated by the

whole structure and behaviour of the carapace and plastron. The softening

of the whole shell, the loss of the horny shields, the reduction of the

claws, are the direct and almost unavoidable results of life in muddy

waters.

Geologically they do not seem to be very old. They appear, already

referable to the genus _Trionyx_, in the Upper Cretaceous strata of North

America. In the Lower and Middle Tertiary strata many species existed in

North America and in Europe, and it is of great importance that in these

species the costal plates were much broader, and the marginal plates better

developed, than in the recent forms. Now their half-dozen genera, with

about twenty-four species, are confined to North America, the tropical and

warmer parts of Asia, and the Malay {407}Islands, and to Africa from the

Nile to the Senegal and to the Congo.

The habits of Trionychoidea have found few observers. According to L.

Agassiz,[138] they live in the muddy bottom of shallow waters, burying

themselves in the soft mud, with only the head, or a small part of it,

exposed. They breathe without moving the body, by raising up the long neck

and carrying the leathery snout above water. When moving through the water

they strike horizontally with both pairs of limbs, alternating, however,

the right and left; but when they start suddenly, the front limbs are seen

moving together towards the tip of the snout, and then striking

simultaneously backward with great power. As the shield does not project

forward, the fore-limbs usually move beyond the shield, and as its outer

edge is sharp, and the feet are broad, their webs reach above as well as

below the plane of that edge, so that the water is driven partly over and

partly under it. When they move along the bottom, the limbs still move

horizontally, the webs striking against the water, and the inner toes,

those with the claws, against the bottom. They also bury themselves

horizontally, becoming covered by only a thin layer of mud. They readily

resort to the shell for protection. The neck and head are withdrawn

entirely, the loose skin rolling off from the greater part of the neck; and

the skin of the legs also slips off, as far as the elbows and knees. In

confinement they exhibit great quickness; their movements are abrupt and

unsteady, except when they swim rapidly in one direction. They then dart

their long and slender neck quickly forwards or sideways and upwards, as

snakes do, and bite in the same way, striking suddenly. Their temper is bad

or even ferocious, and large specimens are quite dangerous.

Their food consists of all sorts of aquatic animals, fish, frogs, and

molluscs, for instance _Anodonta_ and _Paludina_. According to the

different diet, many species develop a peculiar kind of dimorphism, a

reasonable explanation of which has been given by Boulenger. In the young

the horny coverings of the jaws are sharp, with cutting edges, and in those

specimens which keep to a diet of fish and other soft creatures, the jaws

remain in the same condition. But in those which take to living upon

molluscs, the hard shells of which they have to crush, the horny edges are

{408}worn down; and broad, thick, horny, crushing pads are developed in

their stead, the supporting parts of the jaws becoming more massive. The

masticatory muscles are likewise enlarged, and a tubercle grows upon the

lower border of the jugal bone, whence arises part of the masseter muscle.

The eggs are round, thick-shelled, but very brittle; they are laid in the

sand above the level of the water, and this is the chief occasion on which

these tortoises creep on land.

_Trionyx._–The plastron has no special cutaneous valves for the concealment

of the hind-limbs. This is the principal genus, with the greatest number of

species and the widest distribution, the latter coinciding with that of the

whole family. The upper surface of the shell of young specimens frequently

forms numerous longitudinal ridges or series of little horny tubercles

which disappear with age.

_T. ferox_, the commonest "Soft-shelled Turtle" of the United States. Olive

above with scattered, small, round, black spots; young with conical,

spine-like tubercles, especially on the nuchal border and on the posterior

portion of the shell, which has a pale, black-edged border. A light,

black-edged streak passes through the eye and joins its fellow on the

snout. The limbs are olive brown, spotted and marbled with black. The under

parts of the shell are white. Very large specimens have a shell 18 inches

in length and 16 inches wide. Holbrook gives the following account of its

habits:–

"A voracious, carnivorous creature. They reside most constantly in the

water, swim with rapidity, and choose for their retreat holes under the

banks of rivers, or under rocks; and not unfrequently the trunk of some

huge forest tree, fallen into the stream, affords them shelter. Sometimes

they leave the water and conceal themselves in the mud: I have frequently

seen them thus buried to the depth of 2 or 3 inches, leaving only a small

breathing hole for the long neck and narrow head, which is occasionally

thrust out, but most commonly it is retracted so that one would pass near

without observing their habitation; and if seen, it might easily be

mistaken for the residence of some large insect. At other times they may be

seen in numbers on rocks in shallow water, basking in the sun, apparently

asleep. They bite severely when provoked, darting forward with great

velocity the long neck and head, and not unfrequently spring upward at the

same time and make a loud hiss.

{409}[Illustration: FIG. 92.–_Trionyx ferox_ (American Soft-shelled

Turtle). × ⅒.]

In the month of May the females seek sandy places along the banks of the

waters they inhabit to lay their eggs, generally about sixty in number; and

it is remarkable that, though their motions are slow and difficult on dry

land, yet at this season they sometimes mount hillocks several feet high.

The flesh affords the most delicate food, surpassing that even of the Green

Turtle. The geographical distribution is interesting. It inhabits the

Savannah as well as all those rivers that empty into the northern borders

of the Gulf of Mexico; it ascends up the broad Mississippi, and is found in

all its tributaries, even to the very foot of the Rocky Mountains; it

abounds in the chain of great northern lakes both above and below the Falls

of Niagara, and is common in the Mohawk, a tributary of the {410}Hudson

river; but it is not found in any other Atlantic stream between that and

the Savannah river, a distance of nearly 800 miles."

_T. triunguis_, the only African species, ranging from the Senegal and

Congo into the Nile-system, but occurring also in Syria, is perhaps the

largest of all Trionychidae, reaching a shell-length of almost 3 feet. The

adults are olive-brownish above, the throat and under parts of the shell

with round, white spots separated by a dark network. The young have whitish

specks and spots.

[Illustration: FIG. 93.–_Trionyx gangeticus_ (young). × ⅓.]

_T. gangeticus_ and _T. hurum_ are the principal Indian species. The former

is the larger of the two, with a shell of more than 2 feet in length; olive

above, the young with fine black vermiculations; head with a black

longitudinal streak from between the eyes to the nape, intersected by two

or three chevron-shaped black streaks; under parts yellowish. _T. hurum_ is

olive brown above {411}and below, in younger specimens with conspicuous,

large, yellow spots on the sides of the head. The young are ornamented with

two or three pairs of large round spots on the back, and the same applies

to the beautiful young of the Burmese, _T. formosa_.

[Illustration: FIG. 94.–_Trionyx formosa_ (young). × 1.]

The three genera, _Cycloderma_ and _Cyclanorbis_ of Tropical Africa, and

_Emyda_ of India, have a pair of cutaneous femoral valves or flaps on the

plastron, beneath which the hind-limbs are withdrawn.

{412}CHAPTER X

DINOSAURIA–CROCODILIA

_SUB-CLASS V.–DINOSAURIA._

_Mesozoic, long-tailed, toothed reptiles, with distal ischiadic

symphysis, terrestrial limbs, large fixed quadrate bones and bifurcated

ribs._

The Dinosaurs begin and end with the Mesozoic epoch, and have a world-wide

distribution. The name, "terrible Reptiles," refers to the gigantic

proportions which many of them attained, not a few of them surpassing in

size and shape the fantastic pictures of the dragons of our fables.

Although these creatures came to an end millions of years before the first

man-like beings appeared, it is reasonable to suppose that the

widely-spread myths of dragons are based upon the accidentally disclosed

skeletons of these monsters.

The skull is built after a plan which may be derived from a combination of

the Crocodilian and Rhynchocephalian skulls, but the detail varies

considerably in the many and much diversified members of this large

sub-class. There is as a rule a pre-orbital foramen, which is smallest in

the Ornithopoda. The orbit is completely encircled by bones, and the

temporal fossa is divided by a squamoso-postfrontal or post-orbital bridge

into a smaller supra-, and a much wider infra-temporal portion, the latter

being bordered below by the jugal and quadrato-jugal, and this is firmly

connected with the quadrate by an ascending process. The quadrate is long,

more or less vertical in position, slanting either forwards or backwards,

and firmly fixed above by the squamosal, perhaps also by a supra-temporal

bone. The orbit is bordered by the jugal, lacrymal, pre- and post-frontals.

The interparietal foramen seems to be {413}abolished. Teeth, mostly

alveolar and laterally compressed, are restricted to the dentary,

maxillary, and premaxillary bones. In the Orthopoda the latter carry no

teeth, or these are restricted to the lateral portion, leaving a wide

diastema. This toothless part plays upon a peculiar crescent-shaped bone,

the so-called predentary, which rests loosely upon the anterior ends of the

mandibular rami, which latter do not as a rule form an osseous symphysis.

The Ceratopsia possess in addition a similar upper toothless piece, the

prerostral, a kind of pre-premaxilla. The morphological value of these

extra pieces is quite obscure; they were in all probability provided with

thick, horny pads. The bones of the roof of the mouth recall in their

arrangement that prevailing in the Rhynchocephalia and the Parasuchia.

There are two pairs of large vacuities; one between the maxillae,

ectopterygoids and palatines; the other between the latter, the maxillae

and the usually small or slender vomers. The pterygoids are perhaps the

largest bones, and form a rather long symphysis; laterally and behind they

abut against the quadrate, anteriorly against the ectopterygoids and the

palatines, which latter they sometimes separate. A peculiar feature of some

skulls, _e.g._ _Ceratosaurus_ and _Triceratops_ is the great size of the

groove in which the large hypophysis of the brain is lodged.

The vertebrae are very variable, amphicoelous, opisthocoelous, nearly

plain, with a slight concavity behind, or occasionally procoelous in the

anterior region of the tail. Besides the usual pre- and post-zygapophyses

many Sauropoda and Theropoda possess on the posterior trunk-vertebrae

additional joints, effected by a vertical wedge, the hyposphene, which

extends backwards from between the post-zygapophyses and fits into a notch

between and below the anterior zygapophyses of the next following vertebra.

These additional articulations are analogous to the zygosphenes and

zygantra of snakes and iguanas, except that in these Sauria the wedges are

formed on the opposite, namely the anterior ends of the vertebrae. The

vertebrae of the neck and trunk are devoid of intercentra, but those of the

tail carry long chevron-bones. The number of sacral vertebrae is generally

increased to four or five. The ribs have well-developed capitula and

tubercula, and the former have the tendency to shift from the centra or

from their parapophysial processes on to the usually much elongated

diapophyses of the neural arches. This {414}arrangement, recalling the

Crocodilian condition, results in an increased capacity of the dorsal

portion of the body-cavity. Intervertebral articulation of the ribs does

not occur except sometimes in the sacral region. Abdominal ribs are rare,

but they occur in some of the Theropoda, _e.g._ in _Compsognathus_.

The sternum seems to have been mainly cartilaginous, with a pair of

irregular, disc-shaped ossifications. How the coracoids were attached is

unknown; they are small, generally with a foramen, but the scapulae are

always very strong and slant backwards. Clavicles and interclavicles seem

to be absent.

The fore-limbs are as a rule powerful, although often much shorter than the

hind-limbs, which are then enormously developed, and in many genera of two

of the main groups show a tendency towards a semi-erect gait. Some of the

Dinosaurs, e.g. _Iguanodon_ and _Brontozoum_, were absolutely bipedal.

Others seem to have hopped like Kangaroos. In correlation with this more or

less erect mode of progression the iliac bones are very strong, much

elongated horizontally, and attached to more than three, often to five or

even more, vertebrae. The pubic bones show two main types. Each consists

either of a single strong shaft, which is connected distally with its

fellow; or (Orthopoda) this main shaft sends out, below its point of

contact with the ischium, a long process, the so-called post-pubis, which

is directed downwards and backwards. In the latter case it runs parallel

and in close contact with the ischium. Such bifurcated pubic bones never

meet in the middle line. The ischia, on the other hand, are always

connected with each other, not so much by fusion as by syndesmosis.

The hind-limbs exhibit all stages from a simple, plantigrade and five-toed

state to a decidedly digitigrade, four, and even three-toed arrangement.

Many genera exhibit the tendency to form an intertarsal joint, a feature

elsewhere known in birds only, where it is typical and universal. The

astragalus sends up an ascending process which tends to fuse with the

anterior aspect of the distal end of the tibia, and the calcaneum is

sometimes more or less firmly attached to the fibula. In _Compsognathus_

even the distal tarsalia have begun to fuse with the metatarsalia, so that

this reptile at least has a typical intertarsal joint. The femur is

remarkable for the frequent possession of a "fourth" trochanter on the

middle of the inner aspect of the shaft, undoubtedly {415}for the insertion

of the long caudi-femoral or long adductor muscle.

Many Dinosaurs possess hollow instead of solid bones. The vertebrae have

large cavities in the Sauropoda, notably in _Brontosaurus_; in many

Theropoda, e.g. _Coelurus_, _Anchisaurus_, _Compsognathus_, the limb-bones

and the vertebrae are hollow, the latter being reduced to thin-walled

shells with a few inner partitions, the bones being at the same time much

swollen and enlarged. In the Ornithopoda the vertebrae are solid, but the

limb-bones are hollow. The reason of this hollowing out is not easily

found. Undoubtedly it results in a saving of material and weight, whilst at

the same time, without loss of strength, the surfaces for the attachment of

the necessarily powerful muscles are increased. But _Compsognathus_ is a

small, _Brontozoum_ a gigantic, creature. On the other hand, the bones of

the huge Stegosauri are solid. Most probably these cavities were, as in

birds, filled with air-sacs ultimately in communication with the lungs; and

it is by no means a baseless suggestion of Haeckel's that the Dinosaurs

were warm-blooded. Their mode of propagation can only be guessed at from

the circumstance that a rather well-preserved specimen of _Compsognathus_

contains in its abdomen what may possibly be an embryo. There is nothing

against the assumption that the Dinosaurs were viviparous; on the contrary,

it seems more natural than that, for instance, an _Atlantosaurus_ of more

than 100 feet in length and many tons in weight, should have laid eggs.

Some of the herbivorous Dinosaurs, namely, the Stegosauri and the

Ceratopsia, had a dermal armour of variable extent; the plates were loosely

imbedded in the skin, and reached their greatest size along the middle of

the back and tail, and these crested plates were probably covered with

horny scutes, obviously weapons of defence. The Ceratopsia were armed with

a pair of huge pointed horns on the head, and a smaller one on the nose

(see Fig. 102, p. 430). It is difficult to guess the use of the weapons of

these terrestrial monsters, unless they were employed against the equally

large carnivorous Dinosaurs or in the combats for the possession of their

charming mates.

About the ancestry of the Dinosaurs we know nothing except that their

affinities lie with the Crocodilia; but it is impossible to derive either

from the other. The oldest forms, in the {416}present state of our

knowledge–those which have left their three-toed spoors in the Trias of

Connecticut–were already much specialised by having attained to an upright

bipedal gait, while the Sauropoda, which except for their gigantic size are

the most generalised, are of comparatively recent date, none of them being

known from strata older than the Upper Jurassic. Twenty years ago, until

the discoveries of numerous kinds in the United States, our knowledge of

the whole group was very limited. There is a widely spread notion that the

birds have sprung from some Dinosaurian stock. Huxley was the first to show

clearly that birds were an offshoot of the reptiles, and he said of the

Dinosaurs, especially his Ornithoscelida (_Iguanodon_, _Scelidosaurus_,

_Megalosaurus_, _Compsognathus_, and others), that they "present a large

series of modifications intermediate in structure between existing reptiles

and Aves." Baur proved to his own satisfaction that we have to look for the

ancestors of the Ratitae among the herbivorous Dinosaurs, especially the

Ornithopodous forms, whilst the Carinatae are descendants of the Ratitae.

However, even he had to give up this absolutely unwarrantable view.

It is easy to select a considerable number of characters amongst the

various Dinosaurs which also occur in birds, and some of these have until a

recent date been considered as peculiar to birds. For instance, the double,

bifurcated pubic bones of the Orthopoda; the increased number of vertebrae

to which the horizontally elongated ilia are attached, especially in the

forms with an upright gait, and the bipedal feature itself; the possession

of an ascending process of the astragalus and its fusion with the tibia in

_Compsognathus_ and _Ceratosaurus_ among the Theropoda, and in

_Ornithomimus_; the attachment of the distal tarsalia to the metatarsalia,

_e.g._ in _Compsognathus_,–in fact, the formation of an intertarsal joint,

a feature otherwise characteristic of, and peculiar to, birds; the frequent

reduction of the fifth metatarsal bone; the backward position of the hallux

and the proximal reduction of its metatarsal in _Compsognathus_; the

elongation and partial fusion of the functional metatarsals in the latter

genus and in _Ceratosaurus_; the regular increase of the phalangeal numbers

of the first four toes from two to five in many of the Ornithopoda;–in

short, the great resemblance between the feet of some of the Dinosaurs and

those of the birds. However striking these arguments are, they are

instances of {417}convergent analogies. The upright walk, which has been

assumed and improved upon independently by members of both Theropoda and

Orthopoda, has produced the same, or nearly the same modifications in them

as in the birds.

It is easy to show that these features are mere coincidences. The oldest

bird known is _Archaeopteryx_ from the Upper Oolite of Bavaria.

Consequently all those Dinosaurs, which are of the same and of later date,

have to be excluded from the supposed ancestry, and they happen to be those

in which (as in _Ceratosaurus_, _Compsognathus_, _Ornithomimus_,

_Iguanodon_) the resemblances are greatest. There remains only

_Anchisaurus_ of the Upper Trias, more or less contemporary with the

_Brontozoum_, which left its three-toed footprints (_Archaeopteryx_ has

four well-developed toes) with _Zanclodon_. Moreover, the most bird-like

foot is either that of the Theropoda, which, like _Anchisaurus_ and

_Zanclodon_, differ from birds by the formation of the pelvis, or of some

of the latest Ornithopoda. What, then, is the good of selecting a number of

bird-like features from members of Dinosaurs which we are bound to class in

different groups, and which existed, some in the lower, others in the

middle, or even in the latest Mesozoic periods?

Lastly, the advocates of the Dinosaurian ancestry of birds cannot have

fully appreciated the enormous differences between the wing of

_Archaeopteryx_ and the fore-limb of any Dinosaur with the most avian

resemblances in the hind-limbs. The fore-limbs of these reptiles are

modified in a direction diametrically opposed to that from which a

bird-like wing could be developed. The skull presents another

difficulty,and here again _Compsognathus_, a contemporary of

_Archaeopteryx_, comes perhaps nearest to that of a generalised bird's

skull. The ancestors of the birds must have combined the following

characters:–Of not later than Mid-Oolitic age, with bifurcated pubic bones,

four functional toes, elongated metatarsals, complete clavicles,

premaxillary teeth, and free, not firmly fixed quadrate bones. But such

creatures are not Dinosaurs.

We divide the enormous number of Dinosaurs according to the formation of

the pelvis, that of the hind-limbs, and the dentition, into four orders.

{418}ORDER I. SAUROPODA.

_Pubes simple, with symphysis. Premaxillae with teeth. Plantigrade._

The teeth are mostly spatulate, laterally compressed, with sharp edges, but

without serrations. Skull with a pair of large pre-orbital fossae. The

centra of the vertebrae of the trunk have large lateral cavities. The fore-

and hind-limbs are pentadactyle, plantigrade, and hoofed, of the typical

walking type; the bones of the limbs are stout and solid; the femur is

devoid of an inner distal or fourth trochanter. The carpal and tarsal bones

are free. Herbivorous. The Sauropoda comprise some of the most gigantic

terrestrial creatures which have ever existed, compared with some of which

the bulk of an elephant appears almost insignificant. Their range in time

extends from the Lower Oolite into the Cretaceous, with a perhaps

world-wide distribution, namely, Western Europe, North America, Patagonia,

Madagascar, and India. Although they are, except for their size, the least

specialised of all Dinosaurs, none of the Sauropoda hitherto discovered are

old enough to claim to be the ancestors of the other Dinosaurs.

[Illustration: FIG. 95.–Skeleton of _Brontosaurus excelsus_. × 1/180.

(After Marsh.)]

_Brontosaurus excelsus_ of the Upper Jurassic of Wyoming was a giant at

least 60 feet long and about 10 feet high. The head is extremely small in

proportion, not so broad as the fourth of the thirteen vertebrae of the

long and flexible neck. The trunk is comparatively short, the tail longer

than the neck, and provided with numerous chevron-bones. Most of the

vertebrae are hollow, especially the five co-ossified sacrals. The spinal

canal of the sacral region is very wide, indicating a strong sacral

swelling in conformity with the huge posterior limbs. The pubic bones are

stronger than the ischia. The long axis of the {419}former stands almost

vertically like that of elephants, and the knee is scarcely bent in the

erect position. The shoulder-girdle consists of long scapulae, broad at the

base and small, almost square and perforated coracoids, which latter fit

into a pair of partly ossified plates representing the sternum.

_Atlantosaurus immanis_ of the Upper Jurassic of Wyoming and Colorado, is

supposed to have been 115 feet long, perhaps the biggest and bulkiest of

all animals, the femur measuring more than 6 feet in length and 2 in width

at the upper end.

_Morosaurus grandis_, of the Upper Jurassic of Wyoming, with allied forms

in the Purbeck and Wealden of England, reached a length of 30 feet; in

general appearance resembling _Brontosaurus_, but the sacrum consists of

four vertebrae only, and the ischia are bent backwards in their distal

halves, so that their symphysis is formed by the shafts instead of by their

ends.

_Ornithopsis_ and _Cetiosaurus_, likewise huge creatures, from the English

Wealden and from the Great Oolite respectively, are rather imperfectly

known, although several species of each, under many generic synonyms, have

been described.

[Illustration: FIG. 96.–Front view of the pelvis of _Morosaurus grandis_. ×

1/30. (After Marsh.) _a_, First sacral vertebra; _b_, "transverse process"

(rib) of first sacral; _il_, ilium; _is_, ischium; _nc_, neural canal;

_pb_, pubis.]

[Illustration: FIG. 97.–Skull of _Diplodocus longus_. × 1/12 (After

Marsh.)]

_Diplodocus longus_, of the Upper Jurassic of Colorado and Wyoming, is

almost completely known. More than 40 feet long, it had a head in its

general outlines not unlike that of a horse, the skull being about two feet

long. The outer nasal openings are confluent, elongated, and lie far back

on the top of the skull. There is a pair of large antorbital, and a pair of

smaller lacrymal fossae. The teeth, long and slender, are restricted to the

anterior portion of the mouth, with many successors, which, decreasing in

size, lie on the inner or lingual side of the functional tooth, like the

cartridges in a repeating rifle. The {420}functional teeth themselves are

implanted in sockets. The generic name refers to the peculiar

chevron-bones, each half of which diverges into an anterior and a posterior

branch.

It is difficult to understand how these huge, long-necked Sauropoda lived

and moved about. The long neck suggests at first sight predacious habits,

but the teeth, rather feeble in _Diplodocus_, and distinctly of the

plant-cutting type in other genera, put this out of the question. The high

position of the unpaired nasal opening, and the shortened nasal bones of

_Diplodocus_, are features indicative of aquatic habits, but the

short-toed, plantigrade limbs are absolutely adapted to terrestrial life,

and we cannot well assume that such enormous brutes as _Atlantosaurus_

could possibly have ventured into swampy ground.

ORDER II. THEROPODA.

_Pubes simple, with symphysis. Premaxillae with teeth. Digitigrade.

Carnivorous._

The teeth are pointed, recurved, laterally compressed and serrated. The

nasal openings are large, lateral, and nearly terminal. The vertebrae and

the large bones of the limbs are hollow. The fore-limbs are considerably

shorter than the hind-limbs, which are distinctly digitigrade, many of the

species having a pronouncedly upright gait. The proximal tarsalia show a

tendency to fuse with the tibia, and the astragalus has sometimes an

ascending process, by which the fusion with the tibia is strengthened. The

first and fifth metatarsals are often reduced, while the three middle bones

are elongated and sometimes even fused with each other, so that the whole

foot assumes a striking resemblance to that of birds. The terminal

phalanges are protected by curved claws. Owing to the shortness of the

fore-limbs, and the often considerable length of the hind-limbs, which are

strongly bent at the knee and the ankle-joint, these animals must have

progressed somewhat like clumsy kangaroos.

The Theropoda, of which a great number of genera are now known, from the

size of a slender cat to that of an elephant, lived from the Upper Trias to

the Upper Oolite, both in Europe and in North America.

_Brontozoum giganteum_, one of the oldest forms, is known {421}from its

foot-spoors only, which, together with other three-toed spoors in the

sandstone of the Connecticut valley, were originally described and figured

by Hitchcock as _Ornithichnites_ (ἴχνος = track, or spoor). Some of these

imprints are more than a foot in length, the right and left spoors

following alternately at a distance of from four to six feet. In some cases

the long trailing tail has left a furrow behind, and the large tracks are

accompanied or crossed by much smaller, and even by quite tiny tracks,

otherwise similar, and undoubtedly made by the young.

_Anchisaurus_, from the same locality, was still Sauropodous, in so far as

the metatarsals are still free, with two, three, four, and five phalanges

on the first four toes, but the fifth metatarsal is reduced, carrying a

vestige of only one phalanx, and the proximal tarsal bones are fused with

the tibia and fibula respectively. Total length some seven feet, of which

about four belong to the tail.

_Zanclodon_, from the Keuper of Würtemberg, about ten feet long, with

pentadactyle hands and feet. Ischia stronger than the pubic bones, which

are distally much broadened. The femur is nearly three feet long, and

possesses a fourth trochanter. The astragalus has an ascending process, and

is fused with the tibia. The toes are short, strong, and clawed. The

shoulder-girdle and fore-limb are strong, the latter well adapted to

grasping. The teeth are much compressed laterally, with sharp, finely

serrated edges. Several allied genera have been described from the Upper

Trias of France and England: others from corresponding strata of India and

South Africa.

[Illustration: FIG. 98.–Skull of _Anchisaurus coelurus_. × ¼. (After

Marsh.) _a_, Nasal fossa; _b_, antorbital, _c_, infra-temporal, _d_,

supra-temporal, and _o_, orbital fossa; _q_, quadrate bone.]

_Megalosaurus_, from the Trias to the Wealden in England and France, with

other species in Colorado and India, reached a considerable size, larger

than that of any other Theropoda, the scapula of _M. bucklandi_ being

nearly three feet long, and the femur still longer. The hind-limbs are

twice as long as the fore-limbs. The cervical vertebrae are short, the neck

being much shorter than the tail. Hands with five fingers, feet with four

toes. Pubic bones long and slender, with a broad symphysis. With

well-developed abdominal ribs, resembling those of crocodiles.

{422}_Allosaurus_, from the Upper Jurassic of North America, with only

three toes. Ischia and pubes united into one symphysis. Anterior

extremities very short. Sacrum consisting of four vertebrae. Total length

of some of the larger species about twenty feet.

[Illustration: FIG. 99.–Skeleton (× 1/40) and skull of _Ceratosaurus

nasicornis_. (After Marsh.) _a_, Nasal cavity; _b_, bony horn-supporting

excrescence; _c_, pre-orbital fossa; _d_, orbital fossa.]

_Ceratosaurus nasicornis_, from the Upper Jurassic of Colorado, is about

seventeen feet long. The generic and specific names refer to the nasal

bones, which are raised into an unpaired longitudinal crest. This, by its

rough surface, suggests that it was covered by a horny sheath, or carried a

horn. The large skull, about two feet in length, is armed with strong,

slightly curved, laterally compressed, sharp teeth, unequal in size. The

pre-orbital foramen is large, bordered above by the prefrontals, which are

raised into prominent knobs. The supratemporal foramina are extremely

small, the lateral foramina very large. The quadrate slants backwards. The

sacrum consists of five vertebrae. The caudal vertebrae carry long and

slender chevron-bones. The pubes and ischia are long and slender, each

forming a separate symphysis at their broadened ends. The three

{423}metatarsals are elongated and fused with each other. There seems to

have been some dermal armour in the shape of osseous plates, which extended

in one series from the occiput over the neck.

_Coelurus gracilis_, of the Upper Jurassic of Wyoming, and closely allied

forms in the Wealden of England, are remarkable for the pneumaticity of the

centra and processes of their vertebrae, the bony parts of which are

restricted to thin, hollowed-out shells, so that the whole skeleton must

have been very light. Computed length of these imperfectly preserved

creatures about five feet.

_Hallopus victor_, of the Upper Jurassic of Colorado. Anterior extremities

very short, with only four fingers; posterior limbs very long and slender,

especially the tibia; the much elongated metatarsals are separate, the

first absent, the fifth much reduced, so that the foot is tridactyle; the

calcaneum projects like a heel. The ilium is attached to two sacral

vertebrae only; the pubes are slender, forming a narrow symphysis, while

that of the ischia is broad. Most of the bones of this creature, which

probably progressed by hops, are hollow. Total length about three feet, the

length of the hind-limbs being about nine inches.

_Compsognathus longipes_, of the Upper Jurassic of Bavaria, is one of the

smallest of all the Dinosaurs. It is most remarkable on account of its

almost bird-like feet. The fibula is much thinner and somewhat shorter than

the tibia; the latter is closely attached to, although not fused with the

proximal tarsal bones, while the distal tarsals are fused with the united

and much elongated second, third, and fourth metatarsals; the fifth is

reduced to a short bone near the intertarsal joint; while the first is

represented by its distal portion only, which is stowed away on the hinder

aspect of the middle of the second metatarsal, and carries two phalanges.

The three middle toes consist of three, four, and four phalanges

respectively. Whilst the whole hind-limb is typically avian, the pelvis is

quite different; the pubic bones are simple, slender, and directed

forwards, forming a symphysis with their whole distal halves, and

broadening out distally into a horizontal process directed towards the

symphysis, which is likewise formed by the fusion of the inner surfaces of

the thin and rather flat ischia. The fore-limbs are only half the size of

the hind-limbs. The neck consists of about ten vertebrae, mostly with long

and {424}pointed ribs. Tail long with well-developed chevrons. The skull is

long and pointed, composed of thin bones, which have lost most of the

sutures; with large lateral, temporal, and pre-orbital, but without

supratemporal, foramina. Premaxillae, maxillae, and mandible with numerous

slender and rather long, conical, alveolar teeth.

ORDER III. ORTHOPODA

_Each pubic bone consists of an anterior or pre-pubic and a posterior or

post-pubic branch, neither of which forms a symphysis. Premaxillae

without teeth. With a premandibular predentary piece. Herbivorous._

The so-called pre-pubis is homologous with the pubis of most recent

reptiles, and with the pectineal process of birds, while the "post-pubis"

is homologous with the processus lateralis of Chelonians and Saurians, and

with the "pubis" of birds. The right and left halves of the pubis remain

widely asunder ventrally. In many cases the post-pubis, always directed

obliquely backwards, lies closely against the shaft of the ischium, which

always forms a distal syndesmosis, or a symphysis, with its fellow. The

fore-limbs are usually very short, provided with five or four short and

strong fingers. The hind-limbs are long and strong, mostly with three,

sometimes with four functional short toes, either plantigrade (STEGOSAURI)

or digitigrade (ORNITHOPODA). Femur with an inner distal, or fourth,

trochanter. The dentition is of the herbivorous type, restricted to the

dentaries of the mandible and to the maxillary bones, leaving the whole or

the greater part of the premaxillaries free. The additional "predentary"

piece of the mandible is possibly a calcified, but originally horny, pad.

The teeth are greatly compressed laterally, and finely serrated, but are

much ground down by use; several rows of successional teeth lie on the

inner or lingual side. The skull is strongly built, with large anterior

nasal openings; pre-orbital foramina very small or absent; orbits

completely encircled by bones; supratemporal foramina small, lateral

foramina large. Quadrate large, vertical or slanting slightly forwards. The

vertebrae are solid, not hollow; sacrum consisting of four, five, or more

vertebrae; ribs bifurcated, the capitula carried either by the centra, or

moved up to the diapophyses of the neural arches; chevron-bones

{425}numerous, and frequently long, especially on the anterior half of the

long and heavy tail.

Orthopoda occur from the Lias to the Upper Cretaceous, both in Europe and

in North America. The name Orthopoda, invented by Cope in 1866, is

appropriate for obvious reasons; it comprises the Stegosauri and

Ornithopoda of Marsh (1881). The latter term is not very fortunately

chosen, considering that the whole hind-limb of the Theropodous

_Compsognathus_ is far more ornithic than that of any three-toed

Ornithopoda, in which the tarsalia rarely fuse with the tibia and never

with the metatarsals. To apply the term Ornithopoda to the whole order is

quite unjustifiable, unless it is meant to apply to the strikingly

bird-like configuration of the pelvis.

SUB-ORDER 1. STEGOSAURI.–The fore- and hind-feet are plantigrade, or nearly

so, the metapodials being but little elongated, with more than three

functional digits. The bones of the limbs are solid. The ribs of the trunk

are bifurcated, and are carried by the diapophyses of the neural arches.

The body, especially the back, is protected by dermal bony plates, which

are not connected with the internal skeleton.

_Scelidosaurus harrisoni._ One nearly complete skeleton, about 11 feet in

length, from the Lias of Lyme Regis. About twenty-four pre-sacral

vertebrae, of which six or seven belong to the neck, four sacral and about

forty caudal vertebrae. Four fingers, four toes, with 2, 3, 4, 5 phalanges,

the fifth metapodials being quite vestigial; the hallux and pollex are very

short, so that the foot at least is functionally tridactyle. The tarsal

bones remain separate. The head is very small. Two rows of ridged bony

plates extend from the neck over the back, and converge into one row upon

the long tail; smaller plates, arranged in many rows, seem to have

protected the sides and under parts. _Hylaeosaurus_ and _Polacanthus_ of

the English Wealden are allied forms.

_Stegosaurus_, with several species from the Upper Jurassic of Colorado and

Wyoming, and others, e.g. _S. armatus_ (= _Omosaurus_), from the Kimmeridge

Clay of Wiltshire in England. The head is relatively very small, and the

brain is surpassed several times in thickness by the huge sacral swelling

of the spinal cord. Teeth numerous and small. All the cervical and

trunk-vertebrae carry bifurcated ribs, those of the trunk being carried

entirely by the very high neural arches. The fore-limbs are only about half

{426}the length of that of the hind-limbs, so that these creatures, which

were undoubtedly quadrupedal, must have had a very peculiar gait, standing

with the head, neck, and shoulders much lower than the arched back and

pelvic region. The ulna has a strong olecranon; the hand has four

functional fingers. The pre-acetabular portion of the ilium is much

elongated; the pre-pubic branch stands horizontally, while the post-pubis

is closely adpressed to the ischium. The astragalus is fused with the

tibia, the calcaneum with the fibula. The foot has only three short toes,

protected, like the fingers, by hoofs. The dorsal dermal armature consists

of very high, crest-like plates. _S. ungulatus_ of North America has a

computed length of 28 feet, with the hind-limbs about 7 feet long. This

creature was nearly 10 feet high, when measured from the ground to the tips

of the dermal crests on the middle of the back. These bony, laterally

compressed plates are themselves nearly 3 feet high, and are replaced, on

the hinder portion of the tail, by several pairs of pointed spikes about 2

feet in length.

[Illustration: FIG. 100.–Skeleton and dermal armour of _Stegosaurus

ungulatus_. × 1/60. (After Marsh.)]

SUB-ORDER 2. ORNITHOPODA.–The hind-limbs are distinctly digitigrade,

usually with only three functional toes, protected by claws. The long bones

are hollow. Femur with a long fourth trochanter. Without dermal

armour-plates.

_Camptosaurus._–Several species, up to 10 feet in length, from {427}the

Upper Jurassic and the Wealden of North America and England. Five fingers,

with 2, 3, 3, 3, 2 phalanges and four toes, with 2, 3, 4, 5 phalanges, but

the hallux is much shortened and does not touch the hard ground; astragalus

and calcaneum separate.

_Laosaurus_ of Colorado is a smaller form, intermediate in structure

between the former genus and _Hypsilophodon foxi_ from the Wealden of the

Isle of Wight. A small creature, less than 5 feet in length. Four fingers,

with 2, 3, 4, 2 phalanges; fifth metacarpal vestigial. Four toes with 2, 3,

4, 5 phalanges and long claws. Astragalus and calcaneum separate.

Post-pubis very slender. Each premaxillary with five pointed alveolar

teeth, leaving a wide median diastema; maxillaries with eleven, dentaries

with ten laterally compressed blade-like teeth.

_Iguanodon_ from the Wealden of England, Belgium, and Germany. Apparently

two species, _I. mantelli_, about 16 feet, _I. bernissartensis_ nearly 30

feet long. The premaxilla is quite toothless; the teeth of the maxillae and

mandibles stand in close series, implanted in alveolae; they are spatulate,

laterally compressed, with finely serrated edges, and slightly curved, the

lower outwards, the upper inwards, and bear a general resemblance to those

of _Iguana_, hence the generic name. There is only one functional set of

teeth, and these are much worn down by use, but in such a way that, owing

to the different curvature of the opposed teeth, the worn-down crowns form

cutting, and at the same time crushing, almost triturating surfaces,

indicating that these animals lived upon herbs. The gait of these creatures

was upright, as shown by their spoors; the long almost vertical ischia,

which form a padded symphysis, only slightly raised above the ground,

suggest that this symphysis was used as a true sitting support, the animal

resting upon it, the hind-limbs and the long tail. The latter, to judge

from the long chevrons and the high neural spinous processes, must have

been furnished with strong muscles. The whole tail was undoubtedly used as

a balance during the upright position. Many of the tendons of the dorsal

spinal muscles on the back and upper half of the tail are ossified. The

post-pubic branches are very slender, distally much reduced, and, except at

the obturator-foramen, separated from the ischia; the pre-pubes are very

strong and broad. The femur has a fourth trochanter, a feature which

{428}induced the unfortunate late Paul Albrecht to declare that _Iguanodon_

was a reptilian Duck! The tarsal bones are separate. The metatarsals and

toes are reduced to three, with 3, 4, 5 phalanges respectively, the first

being a mere styliform vestige. The anterior limbs are likewise very

powerful, but are much shorter; the hands are adapted for grasping,

possibly for defence and offence, as indicated by the pollex, which,

although short, is transformed into a formidable spur-like weapon, firmly

fixed at a right angle to the other four fingers, the phalanges of which

number 3, 3, 3, 4; the second and third fingers were protected by hoof-like

nails, the fifth finger is feeble, and stands somewhat apart. The whole

vertebral column consists of more than eighty vertebrae, of which ten are

cervical, eighteen thoracic and lumbar, while five or six are fused into

the sacrum. The cervical vertebrae are opisthocoelous, and carry short

ribs, except the atlas, which possesses two separate supra-dorsal pieces,

which fill the gap between it and the occiput.

[Illustration: FIG. 101.–Skeleton of _Iguanodon bernissartensis_. × 1/80.

(After Marsh.)]

Many specimens of _I. bernissartensis_, which is now completely known,

including even the hyoid bones, were discovered in 1878, in the Belgian

colliery of Bernissart, between Mons and Tournai, close to the French

frontier. The bones were in a fault or crack, filled with clay of Wealden

age, about one thousand feet below the present sea-level, and there about

thirty Iguanodons, all {429}apparently adult, had become embedded. Five of

them are now mounted in one of the public galleries of the Brussels Museum,

of which these perfect monsters form one of the chief attractions. Having

proved to be such a valuable find, they were claimed by the Government, on

the ground that Iguanodons were not included in the license of the Coal

Mining Company. The fact that not only _I. bernissartensis_, but also a few

specimens of _I. mantelli_, already known from England, where the large

form likewise occurs, were found in the same place, makes the specific

differences somewhat doubtful; they are perhaps sexual.

_Claosaurus_ of the uppermost Cretaceous strata of Wyoming, is one of the

latest of Dinosaurs. It is nearly allied to _Iguanodon_, but has only three

functional fingers, the fifth being absent, whilst the pollex is very

short.

_Hadrosaurus_ s. _Diclonius_ of the same level as the preceding genus in

North America, apparently also in the Middle and Upper Chalk of England and

Belgium, has a most peculiar spoon-shaped bill, the premaxilla and the

predental bone being spatulate and quite toothless. The teeth in the upper

and lower jaws are numerous and small, and whilst one set of teeth is being

ground down, the several successional series are already functional. _H.

mirabilis_ has in all about 2000 teeth; the total length of the skeleton is

38 feet, of which nearly 4 feet are taken up by the skull; in other

respects this genus is allied to _Iguanodon_.

_Ornithomimus_, of the Upper Cretaceous of Colorado, is known only from its

fore- and hind-limbs. The fore-limbs are short, with three fingers. The

hind-limbs are very long and strikingly bird-like. The metatarsals, of

which only the second, third, and fourth are developed, are much elongated;

the proximal half of the third is pushed back between the second and

fourth, and imperfectly fused with them, exactly as in young birds. The

astragalus has a long ascending process, and is fused with the tibia. The

fibula is very slender, distally much reduced; the calcaneum is represented

by a tiny nodule; the terminal phalanges end in pointed claws. _O. grandis_

must have reached a considerable size, to judge from its middle metatarsal,

which is 60 cm. or 2 feet long. Until more is known of these extraordinary

creatures, nothing definite can be said about their affinities. They may

perhaps belong to the Theropoda.

{430}ORDER IV. CERATOPSIA.

_Pubic bones simple, forming a symphysis, post-pubic branches being

absent. The mandible carries a toothless "pre-dental," and the fused

premaxillaries carry a similar, toothless, "rostral" bone._

The teeth of the upper and lower jaws are alveolar, and have two roots. The

fore-limbs are little shorter than the hind-limbs; pentadactyle and

plantigrade, with broad hoofs. Femur without a fourth trochanter.

Limb-bones solid. The skull is large, and remarkable for a pair of long

frontal bony cores, which probably carried large, pointed horns; the

parietal bones form a huge, horizontally broadened out crest, which extends

backwards over the neck. Upon this cranial neck-shield follow small dermal

bony plates. These miraculous creatures flourished during the Cretaceous

epoch in Europe and in North America. Some, for instance, the American

_Triceratops flabellatus_, reached a huge size, its skull alone measuring

more than 5 feet in length, while that of _T. prorsus_ is, including the

neck-shield, about 7 feet long. The total length of this monster, the back

of which stands about 8 feet high, is more than 20 feet. Other genera seem

to have a well-developed dermal armour, _e.g._ _Nodosaurus_ of the Middle

Cretaceous period of Wyoming.

[Illustration: FIG. 102.–Skeleton of _Triceratops prorsus_. × 1/70. (After

Marsh.)]

The Ceratopsia combine characters of the Sauropoda and of the Stegosaurian

Orthopoda; in their pelvis they agree with the former, in the development

of dermal armour and a predental bone they agree with the latter, while

they differ from either by the possession of a rostral element.

{431}_SUB-CLASS VI.–CROCODILIA._

If we had to deal only with the recent Crocodilia the following would be an

all sufficient diagnosis:–_Four footed, long-tailed reptiles, with fixed

quadrate bones, with teeth separately implanted in alveolae and restricted

to the upper and lower jaws._

[Illustration: FIG. 103.–1, Atlas and axis of _Crocodilus_. 2, Atlas and

axis of _Metriorhynchus_, a Jurassic Crocodile, see p. 439. 3, Analysis of

the first two cervical vertebrae of a Crocodile. 4, Diagram of the

fundamental composition of a Reptilian or other Amniotic, typically

gastrocentrous vertebra. _Az_, Anterior zygapophysis; _B.D_, basidorsal;

_B.V_, basiventral; _C_{1}_, _C_{2}_, first and second centra, formed by

the interventralia; _Cp^1_, _Cp^2_, articular facets of the capitular

portions of the first and second ribs; _I.V_, interventral; _N_{1}_,

_N_{2}_, first and second neural arch, formed by the basidorsalia (_B.D_ in

4); _Od_, odontoid process = first centrum; _Pz_, posterior zygapophysis;

_R_{1}_, _R_{2}_, ribs; _Sp_, detached spinous process of the first neural

arch; _t_{1}_, _t_{2}_, facets of the tubercular portions of the first and

second ribs; 1, 2, intercentra = basiventralia; ^2 (in 3), second

basiventral "complex or intercentrum," continued upwards as a meniscus or

intervertebral pad; _I_, _II_, _III_, position of the exit of the first,

second, and third spinal nerves.]

To define Crocodilia in general and to distinguish them from various

extinct groups we have to resort to additional characters. The vertebrae

are solid; the ribs of the neck and thorax possess a distinct capitulum and

tuberculum; there is a series of loose, compound abdominal ribs; the

humerus is devoid of an entepicondylar foramen; the iliac bones are

broadened out and attached to two sacral vertebrae; the pubic bones are

simple, not bifurcated, and neither they nor the ischia are ventrally

united. The skull always has a strong, bony, quadrato-jugal arch. The

possession of a longitudinal cloacal opening and of {432}an anterior or

ventral single copulatory organ can of course be asserted of recent forms

only.

In spite of these many characters common to all Crocodilia, it is very

difficult to separate the latter from the Dinosauria, the only absolute

difference lying in the ventral pelvic bones. It is therefore most

suggestive that the fore-limbs of the Mesozoic Crocodilia are so much

shorter and weaker than their hind-limbs, a discrepancy which is not

lessened before the Tertiary epoch. The Mesozoic Crocodilia were almost

entirely marine; the strongly-developed ankle-joint (indicated already by

such early forms as _Aetosaurus_ and _Mystriosaurus_) must have been

inherited from some terrestrial group with digitigrade tendencies and

shortened hind-limbs. All this points to some Theropodous Dinosaurian stock

of which the Crocodilia may well form an aquatic, further-developed branch.

Loss of the pubic and ischiadic ventral symphysis is not a serious

modification. So far as modern reptiles are concerned only the Chelonia and

_Sphenodon_ are related to the Crocodilia, whilst Monitors and other

lizards resemble them only superficially. We divide them into three Orders.

ORDER I. PSEUDOSUCHIA.

The few members of this peculiar group of reptiles are all restricted to

the Keuper or variegated marls, although they seem to have had a wide

distribution, some having been found in Germany, others in New Mexico. They

perhaps form an early side-branch of the generalised Crocodilian stock,

which died out with the Jurassic age.

The skull is distinctly short and pointed. The premaxillaries are very

small and are dorsally separated from each other by the large nasals, which

also keep the maxillae widely asunder. The nostrils are latero-terminal,

bordered chiefly by the nasals, below by the premaxillae and part of the

maxillae. The orbit is bordered below by the strong jugals, in front by the

prefrontal, above by a supra-orbital and a small postfrontal, behind by a

postorbital, which, firmly connected with the jugal and squamosal, shuts

off a supratemporal foramen. There is also a lateral temporal fossa, and a

large hole enclosed by the lacrymal and the maxillary bones. The teeth are

restricted to the anterior {433}half of the jaws. The neck, back, and tail

are covered by two rows of large and broad, closely-jointed bony plates;

smaller plates protect the sides and the ventral surface. The vertebrae are

still unknown.

_Aëtosaurus ferratus_ of the Upper Keuper near Stuttgart is the best known.

One of the greatest treasures of the Stuttgart Museum is a slab of

sandstone, about 2 square yards in size, upon which lie huddled together

twenty-four individuals of various sizes, the largest measuring 86 cm. or 2

feet 10 inches. They are in a beautiful state of preservation, and many of

them are in the most life-like attitudes, just as if a mass of sand had

fallen upon them and crushed them down, and as if they were struggling to

get out.

_Erpetosuchus_ and _Ornithosuchus_ of the Elgin sandstone seem to be allied

forms.

ORDER II. PARASUCHIA.

As the name implies, a collateral branch of the true Crocodilia. They are,

like the Pseudosuchia, restricted to the Keuper formation. The vertebrae

are mostly biconcave, sometimes with nearly plain, scarcely concave,

central joints. The premaxillae are very long and powerful. The nostrils

lie far back, rather near the orbits, on the top of the snout, within the

anterior half of each nasal and almost above the choanae. The latter are

situated in front of the palatine bones and are divided by a backwardly

directed process of the vomer, which is plainly visible on the roof of the

mouth. The palatines and pterygoids leave a wide median space between them.

The pterygoids are narrow and have three processes, the antero-lateral of

which joins the palatines and the maxillary bones (there being no separate

ectopterygoid), the inner joins the basi-occipital, and the postero-lateral

the quadrate.

The orbit is surrounded by the frontal, prefrontal, lacrymal, postorbital

and postfrontal, while the strong jugal is excluded. The temporal region

shows a lateral and a dorsal foramen; the latter opens backwards and above

the occiput, being bordered in front by the parietal, laterally by the

squamoso-occipital bridge.

The vertebrae are amphicoelous. The first and second {434}vertebrae are

devoid of ribs; the cervicals and first thoracics carry separate capitular

and tubercular processes for the attachment of the ribs, while the ribs of

the rest of the trunk are carried entirely by the long diapophyses, as in

the modern Crocodiles. The dermal armour consists of two rows of broad,

dorsal, and several rows of smaller, lateral, bony plates.

_Belodon_ is by far the best-known genus, with several species in South

Germany and North America, some of which reached a length of 10 feet,

without ventral armour. The closely allied _Stagonolepis_ of the Elgin

sandstone in Scotland had dorsal and ventral armour. Other genera in the

Triassic formations of India and North America.

ORDER III. EUSUCHIA.

Crocodilia in the stricter sense. The premaxillae are short and always

enclose the nostrils. The choanae lie behind the palatines, in recent forms

even within the pterygoids. They occur from the Liassic or Lower Jurassic

period to the present time.

The direct ancestors of the Eusuchia are still unknown. They cannot have

been developed from the Pseudosuchia, nor do we know intermediate stages

which connect them with the Parasuchia. The nostrils, situated within the

premaxillaries, always lie in front of the nasals, although these sometimes

extend forwards and form a bony internasal septum fusing with the usual

cartilaginous septum. The choanae, instead of opening immediately behind

the vomer, are carried far back, owing to the formation of a secondary bony

palate. In the Jurassic Crocodiles this roof is formed by the meeting of

the palatine bones in the medio-ventral line, and the choanae open

immediately behind. From Cretaceous times onwards this roofing is continued

by the pterygoids, which likewise form a median suture; and the united

choanae (which may, or may not, be divided by a thin bony septum) are

pushed towards the posterior end of the pterygoids. Since the Jurassic

times there exists also a tendency to enclose the Eustachian passages (the

remnants of the first gill-clefts) by bone. In the earlier members they

were still wide slits or open grooves on the ventral side of the

basi-occipital bone. Since the Cretaceous epoch they have been transformed

into bony canals and open through one median hole, situated between the

basi-occipital and the {435}basisphenoid, immediately behind the posterior

symphysis of the dorsal portion of the pterygoids, which latter almost

completely cover the basisphenoid. The vomer is not visible (except in

_Caiman niger_), being covered by the ventral junction of the palatines and

maxillaries. The broad, lateral wings of the pterygoids are connected by

separate bones, the ectopterygoids = transpalatines = transverse bones,

with the maxillaries, and in recent forms also with the jugals. Thus an

extensive, very firm bony palate is produced; and the large palatal

foramina, between the palatines, maxillaries, ectopterygoids and

pterygoids, are closed by the same dense mucous membrane which cover the

whole roof of the mouth.

The opisthotic and epi-otic bones fuse early with the lateral and with the

supra-occipital bones; only the pro-otic remains longer as a separate

element, perforated anteriorly by a large hole for the exit of the third

branch of the trigeminal nerve. The basisphenoid is scarcely visible, being

covered by the pterygoids. The presphenoid is large, continued forwards and

upwards into the usually cartilaginous interorbital septum. Near the

anterior and upper margin of the presphenoid is a large notch on either

side for the passage of the optic nerve, the three eye-muscle nerves and

the first branch of the trigeminal nerve. There are no separate

orbito-sphenoids, their place being taken by membrane or cartilage in

continuation with the interorbital septum, but the alisphenoids are large,

abutting upwards against the frontals. Each prefrontal sends down a

vertical process which joins the palatine of its side.

The configuration of the snout varies much. There are two parallel lines of

development since the Jurassic epoch, namely, long-snouted creatures, of

which two still survive as _Gavialis_ and _Tomistoma_, and more broad and

short-snouted members like the rest of the Crocodiles and Alligators. In

opposition to the Parasuchia the elongation of the snout is effected by the

maxillaries. The length of the nasals varies much, mostly in conformity

with that of the maxillaries. As a rule they reach the premaxillaries but

not always the nasal groove. In _Gavialis_ they are short, far separated

from the premaxillaries by the maxillaries, which meet in the dorso-median

line. The orbit is bordered by the frontals, which at an early age fuse

into an unpaired piece, and by the prefrontal, lacrymal, jugal, and

postfrontal. {436}At a deeper level the orbit is partly divided from the

lateral temporal fossa by a strong column which is formed by the meeting of

a downward process of the postfrontal with an inner process of the jugal,

and an ascending process of the ectopterygoid (cf. Fig. 108, p. 458). This

arrangement adds considerably to the strength of the skull. The lateral

temporal fossa is bordered in front by the column just described; below by

the jugal and the quadrato-jugal, which is firmly wedged in between the

jugal and quadrate; behind by the quadrate; above by the postfrontal, which

forms a strong superficial bridge with the squamosal. This rests upon and

often fuses with the quadrate and an intervening transverse wing-like

extension of the lateral occipital bone. By this squamoso-postfrontal

bridge part of the original temporal fossa is divided into the lateral one

just described, and a dorsal fossa. The latter is bordered by the

postfrontal, squamosal, and united parietals. This dorsal temporal fossa is

consequently not homologous with that of the Parasuchia, a vestige of which

is however present in many, especially in young skulls of Crocodiles, in

the shape of a narrow passage which extends backwards from the dorsal

fossa, bridged over by the junction of the parietal with the squamosal, and

bordered below by the occipitals.

The size of the upper temporal fossae stands in an inverse ratio to that of

the lateral fossae. In the older Eusuchia the upper were the larger of the

two. The temporo-mandibular muscle which lifts or shuts the lower jaw

arises from the walls of the upper fossa, passes beneath the jugal arch,

and is inserted into the supra-angular portion of the lower jaw. In the

more recent Crocodiles this muscle is more and more superseded by the

pterygo-mandibular muscle, which, arising chiefly from the dorsal surface

of the much broadened-out pterygoid bone, fills the widened space between

the latter and the quadrate, and is inserted into the outer surface of the

os angulare of the lower jaw. This muscle, owing to its general

disposition, is capable of much more powerful development and leverage than

the temporo-maxillary muscle, which latter, being more reduced, allows the

dorsal fossae to be more and more closed up by the surrounding bones.

The fossae are still comparatively large in the long-snouted genera

_Gavialis_ and _Tomistoma_, which live entirely upon fish and scarcely chew

their food, whilst these holes almost completely {437}disappear in some of

the Alligators, namely in the broad- and short-snouted members, which,

having a varied diet, taken from every available group of the animal

kingdom, chew their prey.

The quadrate extends obliquely backwards, and is immovably wedged in and

partly fused with the quadrato-jugal, the squamosal, and the lateral

occipital wings. Between the latter and the quadrate remains a slit-like

canal, well visible from behind, through which passes the continuation into

the mandible of the columellar or ossicular chain of the auditory

apparatus. Intricate passages, used as additional enlargements of the space

of the middle ear, pervade the proximal portions of the quadrate and the

roof of the cranium beneath the parietal bridges mentioned above, the two

sides communicating with each other. The supra-occipital bone is visible

from behind; its top is covered and partly fused with a continuation of the

parietals, which are, like the frontals, fused into an unpaired mass. The

occipital condyle is formed entirely by the basi-occipital bone, so far as

the articulating facet is concerned, but it is supported on either side by

a lamella from the lateral occipitals.

The two halves of the lower jaw form a symphysis of very variable length.

Each half is composed of six bones. (1) The articulare, perforated in its

upper, posterior, inner corner by a canal for the reception of the

siphonium, a narrow tube of connective tissue, which connects the cavities

of the middle ear with the large empty space enclosed within the lower jaw;

(2) the angulare; (3) the dentary, which alone carries the teeth; (4) the

splenial, a long splint-like bone on the surface of the inner or median

side of the jaw, of variable length; (5) the operculare, the counterpart of

the splenial on the outer side; (6) the supra-angulare, which forms the

dorsal border of the lower jaw between the dentary and the angulare.

The teeth, which are more or less conical or compressed laterally, are

deeply implanted in separate sockets. They are often shed throughout life,

the successors lying on the median side, and with their caps partly fitting

into the wide, open roots of the teeth to be expelled. The number of teeth

in the premaxilla is universally five on either side in recent forms, but

in a few species, e.g. _Crocodilus niloticus_ and _C. porosus_, the second

pair is lost with maturity and is not replaced. In the broad-snouted

{438}kinds, especially in the Alligators, most of the upper teeth overlap

laterally those of the lower jaw. In most species of _Crocodilus_ the

overlapping is less marked and the teeth partly interlock, but the fourth

mandibular tooth, generally the strongest and longest, is received into a

lateral notch at the junction of the premaxillary and maxillary. Frequently

those of the longer lower teeth which fit into pits of the upper jaw,

gradually transform the pits into holes by continued pressure upon the

bone, and in old specimens the tip of the lower tooth may even perforate

and stand out above the skin of the snout.

The vertebrae are solid, but remnants of the notochord persist for a long

time in the middle of the centra. These are still amphicoelous in the

Jurassic Eusuchia, and there were probably considerable intervertebral

portions of the notochord. From the Lower Chalk onwards the vertebrae are

procoelous, with the exception of the first caudal vertebra, which has a

knob at either end, so that naturally the posterior of the two sacral

vertebrae is opisthocoelous. This peculiar formation of the first caudal is

probably correlated with the flexibility of the tail.

Cartilaginous intercentral rings, pads or menisci, occur regularly

throughout the vertebral column, unless they are abolished by fusion of

adjoining vertebrae. It is most instructive to follow the attachment of the

ribs in one and the same individual. The position of the capitulum,

vertically below the tuberculum in the neck, changes in the thorax into one

in which the capitulum lies anterior to the tuberculum and in the same

horizontal plane with it. Moreover, whilst on the cervical vertebrae the

capitulum is carried by the centrum (enclosing with the tuberculum a

typical transverse canal for the vertebral artery, etc.), further back it

moves its point of attachment upwards, lying right upon the neuro-central

suture on the tenth and eleventh vertebrae. From the twelfth vertebra

backwards both capitulum and tuberculum are carried by the transverse

process or diapophysis of the neural arch. The ribs of the five or six

lumbar vertebrae are merely vestigial or absent. The ribs of the two sacral

vertebrae are very stout, fusing in the adult with both centrum and neural

arch. Some of the anterior caudal vertebrae also carry ribs, attached

across the neuro-central suture; long before maturity they fuse with their

vertebrae, and then look like transverse processes. Most of the caudal

vertebrae carry also a {439}pair of chevron-bones, and these are continuous

with the intercentral rings of cartilage.

The atlas and the epistropheus or axis are of supreme interest. Crocodiles

are, in fact, the only animals in which these two vertebrae retain all

their constituent hard parts in an almost undisturbed primitive condition

(Fig. 103, 1-4). The basal piece of the atlas-ring, the first basiventral

or intercentrum, carries a pair of long ribs attached by their capitular

portions. A small knob near the dorsal edge of the rib occurs in many

specimens, and is the last remnant of the tubercular portion. The latter

was still complete in Jurassic Crocodiles, for instance in _Metriorhynchus_

(Fig. 103, 2, _t_{1}_). The first centrum joins that of the second vertebra

as its so-called odontoid process, not directly, however, but by the

intercalation of the complete second basiventral, represented by a

cartilaginous disc, and by a large unpaired pyramidal piece (Fig. 103, 3,

^2). This, serially homologous with the ventral half of the atlas-ring, is

the second basiventral intercentrum, wedged in from below between the

odontoid process and the second centrum, with which it soon fuses.

Moreover, it carries the capitulum of the second rib (2, _Cp^2_), the

tuberculum of which is articulated with a facet of the second neural arch

in Jurassic Eusuchia (_t_{2}_). In recent Crocodiles this tubercular

portion is much reduced, and, curiously enough, is attached to a knob which

belongs to the odontoid piece or first centrum. This shifting explains the

apparently anomalous condition that "the atlas of the Crocodiles carries

two pairs of ribs, the second vertebra none." To complete the account of

the atlas we have to mention the separate unpaired piece which lies upon

the two neural arches. It is the detached neural spine, and not the remnant

of a "pro-atlas."

The first and second ribs (_R_{1}_ and _R_{2}_), at least in the recent

forms, are very long and are quite movable. Those of the next five cervical

vertebrae are firmly fixed, short, and adze-shaped. The eighth and ninth

are again long, and make the transition to the thoracic ribs, which are

mostly eight in number, some with uncinate processes. Then follow several

shorter or floating ribs, mostly two or three pairs. The next following

three presacral vertebrae carry no ribs. The two sacral and the caudal ribs

have already been mentioned.

As a rule the vertebral column of recent Crocodiles, Alligators, {440}and

Gavials is composed of twenty-six precaudal vertebrae (namely, nine

cervical, fifteen thoracic and lumbar, two sacral), and about thirty-four

to forty or more caudal vertebrae. Individual variations, including

lop-sided attachment of the iliac bones, are by no means uncommon.

The sternum remains cartilaginous. It consists of an anterior rhomboid

portion, which carries the coracoids and two pairs of ribs, and a posterior

longer and narrower portion formed by the median fusion of the next

following five or six ribs. Posteriorly the sternum bifurcates, each half

carrying two or three ribs, of which the last sometimes loses its proximal

connexion, and thus appears as a xiphisternal process. Ventrally, upon the

anterior part of the sternum lies the longitudinal, originally paired,

episternum. The shoulder-girdle consists of the coracoids and the scapulae,

which fuse with each other into one bony piece on each side. A pre-coracoid

is indicated in fossil forms by a notch in the coracoid.

The space between the posterior end of the sternum and the pubic bones is

occupied by the so-called abdominal sternum, composed of seven pairs of

ossifications, resting upon the ventral side of the rectus abdominis

muscle. Each pair consists of two closely apposed pieces, while the right

and left remain separate in the median line. The last pair is much stronger

than the rest, is more deeply imbedded in the rectus muscle, and is loosely

connected with the anterior margin of the two "pubic" bones.

The limbs are built upon the typical terrestrial pentadactyle type, but

were in the Jurassic species undoubtedly more adapted to swimming

locomotion. The fore-limbs were conspicuously shorter and smaller than the

hind-limbs, and it is only since Tertiary times that the difference has

decreased to a great extent. Ulna and radius remain separate. The proximal

row of carpal bones consists now of the ulnare and radiale, both strong and

distinctly elongated. On the outer side, between ulna and ulnare, lies a

pisiform bone. Upon the radiale follows a compound bone, often imperfectly

ossified towards the median side, and consisting of the first distal

carpal, the centrale, and the intermedium. The third, fourth, and fifth

carpals are fused into one mass. The second distal carpal remains separate.

All five fingers are present and well developed. The number of phalanges of

the pollex is two, of {441}the others three, four, four and three

respectively. During the embryonic development the number of phalanges of

the fourth and fifth finger increases temporarily, to as many as seven on

the fourth, to five or six on the fifth finger. Before the young animal is

hatched the numbers are reduced again, chiefly by fusion of adjoining

phalanges. This hyperphalangeal condition, typical of Plesiosauri,

Ichthyosauri, Cetacea, and several other absolutely aquatic animals,

naturally suggests the descent of the present Crocodiles from more

essentially aquatic ancestors, but hitherto no trace of supernumerary

phalanges has been found in any Jurassic Eusuchia, nor in the Parasuchia

and Pseudosuchia.

The composition of the pelvis is difficult to understand. It consists in

the adult stage of three separate bones, of which two only partake in the

formation of the acetabulum. The broad ilium sends out two processes; the

posterior and stronger articulates with the ischium, which sends out a

short and stout process towards the anterior process of the ilium,

enclosing a foramen. This process contains a separate centre of

ossification, possibly homologous with the true pubis, while each

club-shaped bone, loosely attached to it and directed forwards, generally

called the pubis of the Crocodiles, would then be equivalent to an

epipubis. Neither the "pubes" nor the ischia form a ventral median

symphysis.

The femur is devoid of a prominent inner trochanter. Tibia and fibula are

of almost equal strength. The tarsal elements are, in the adult, reduced by

fusion to five bones. The fibulare is transformed into a typically

projecting, heel-shaped calcaneum, while the intermedium is fused with the

tibiale into a broad astragalus. The first, second, and third distal

tarsalia are much reduced towards the inner side, and form one

wedge-shaped, partly cartilaginous mass. The fourth tarsale lies between

the fibulare and the fourth metatarsal, while the fifth tarsale is

hook-shaped and loosely attached to the outer side of the fourth. It has

lost its metatarsal and the rest of the fifth finger. Embryos are

hyperphalangeal, the fourth toe developing six phalanges, and there are

traces of the fifth toe. The numbers are ultimately reduced to 2, 3, 4, 4,

0 on the five toes. The fourth toe remains without a claw.

SKIN.–The epidermal horny layer is not shed periodically nor in pieces; the

wear and tear is made good imperceptibly. The {442}scales, which cover the

whole body, have a hard, horny, waterproof covering, but between them the

skin is soft. Each scale of the sides, belly, and tail, and especially

those of the lower jaw, shows a little dot or pit. At this spot the

epidermis is not cornified or thickened, and a nerve with sensory

corpuscles ends beneath the bottom of the pit. Sometimes these pits are

filled with débris of cells, and on the lower jaw, especially on the chin,

these organs, instead of forming pits, are raised into little wartlike

prominences.

The scutes or dermal portions of the scales consist of thickened, cutaneous

connective tissue, and are more or less extensively ossified, thus forming

a proper dermal armour. In most recent Crocodilia the armour is restricted

to the back, with occasional osseous plates on the throat, as in

_Osteolaemus_; regular although thin ossifications in the ventral scutes

occur in the Caimans only. The Crocodile and Alligator skins of commerce

consist entirely of the tanned cutis, minus the epidermis and the horny

coverings of the scutes. In some fossil genera the ventral armour was

extensively developed, especially in _Teleosaurus_, in some genera to the

exclusion of dorsal ossifications. The armour of the recent forms consists,

so far as the large scutes are concerned, of a considerable number of

scutes, which are arranged in transverse rows, each row corresponding with

one skeletal segment of the trunk proper. Mostly there is a detached

cluster of scutes on the back of the neck. On the trunk some of the scutes

are larger and more crested than others, and form in their totality a

variable number of longitudinal rows. The median pair is generally the most

conspicuous on the back. Some of the more lateral rows of keeled scutes

converge more and more towards the tail, the inner rows drop out

imperceptibly, and two lateral rows combine on the middle of the tail into

an unpaired series of vertical blades. These are no longer bony, but show

more strongly developed horny sheaths; they are very flexible, and

transform the tail into an effective propelling organ.

Most of the larger scutes and the upper surface of the bones of the skull

have a peculiar gnawed-out, almost honeycombed appearance, as is usual

wherever most of the cutis itself is transformed into bone or co-ossifies

with underlying bone, while the uppermost layers and the horny layer of the

epidermis are much reduced and thinned out.

{443}All the recent Crocodilia possess two pairs of skin-glands, both

secreting musk. One pair is situated on the throat, on the inner side of

the right and left half of the lower jaw. The opening of the gland, visible

from below (see the figure of _Crocodilus niloticus_, p. 461), is

slit-like, and leads into a pocket, which in large specimens is of the size

of a walnut; the bag is filled with a smeary pale brownish substance, a

concentrated essence of musk, much prized by natives. The secretion is most

active during the rutting time, when the glands are partly everted. My

young Crocodiles and Alligators often turned them inside out, like the

finger of a glove, when they were taken up and held by force. The other

pair lies within the lips of the cloacal slit, and is not visible from the

outside. The use of these strongly scented organs, which are possessed by

both sexes, is obviously hedonic. The sexes are probably able to follow and

find each other, thanks to the streak of scented water left behind each

individual.

The TONGUE is flat and thick, attached by its whole under-surface, so that

it can be elevated but not protruded. It fills the whole space between the

two halves of the lower jaw behind their symphysis. The dorsal surface

shows numerous irregular polygonal fields, in the middle of most of which

opens the duct of a large mucous gland. Tactile and gustatory corpuscles

are scattered over the surface in the shape of tiny wartlike elevations.

The hinder margin of the tongue is raised into a transverse fold, which, by

meeting a similar fold from the palate, the velum palatinum, can shut off

the mouth completely from the deep and wide cavity of the throat, which

leads of course into the gullet. Dorsally the choanae open into this

cavity; and since the narial passages are transformed into long tubes,

completely surrounded by bone, Crocodiles can lie submerged in the water,

with only the nostrils exposed and with the mouth open, and breathe without

water entering the windpipe. The opening of the latter, the glottis, is a

longitudinal slit, protected by the laryngeal cartilages, opened and closed

by muscles. There is also a pair of membranous folds within the glottis,

which serve as vocal cords. Ventrally below the larynx lies the

cartilaginous, broad, shield-shaped hyoid; on the sides are attached the

short hyoid horns. The TRACHEA is long, consists of about sixty or more

complete cartilaginous rings, and divides into two short bronchi, likewise

protected by complete rings. The trachea is depressed; its transverse

diameter decreases {444}from the glottis backwards. The LUNGS have attained

a high degree of efficiency. Each lung is an oval sac, and is transformed

into a complicated system of tubes, at the end of which are the countless

honeycomb-like respiratory cells, the whole lung being spongy. The main

bronchus is continued straight down to the posterior end of the lung, and

sends off during its course regular secondary bronchi, and these send off

tertiary bronchi. The whole arrangement is very regular, the tubes coming

off like rows of organ-pipes. Each lung hangs freely in the thoracic

cavity. Besides its ventral attachment by its arteries, veins, and the

bronchus, it is connected by loose tissue with the liver and the

pericardial septum. Each half of the thoracic cavity is partitioned off

from the abdominal cavity by a strong transverse mesenteric lamella. The

partition between the lungs and the stomach is at first simple, it then

divides, to enclose the liver; the anterior partition passing between liver

and lung to the inner surface of the sternum; the posterior lamella between

the liver and the stomach. Both meet on the ventral surface of the liver,

and are continued into or attached to the peculiar "diaphragmatic" muscle.

This is covered by the internal rectus muscle of the abdomen, arising from

the last pair of abdominal ribs near the pubic bones; it is innervated by a

branch of the last precrural nerve, and extends as a broad but thin

muscular sheath (always within and unconnected with the abdominal wall) to

the ventral posterior vein of the liver; thence it is continued as an

aponeurosis, together with the peritoneal lamella mentioned above, to the

inner surface of the sternum. Contraction of this singular muscle

indirectly widens the pulmonary cavity, and thereby directly aids

inspiration. It acts consequently like the diaphragm or midriff of Mammals,

although it is morphologically an entirely different muscle.

The STOMACH is smaller than one might expect from the fact that large

Crocodiles can eat up nearly a whole man; but a great deal of their prey is

stowed away preliminarily in the wide gullet until the rapid, powerful

digestion, which dissolves every bone, makes room in the stomach. This

consists of a wide, somewhat globular gizzard, rather muscular, with a pair

of tendinous centres like those of birds, and a much smaller pyloric,

globular, more glandular compartment. It leads into the duodenum, which is

coiled up into a double loop, and receives at its end the {445}hepatic and

pancreatic ducts. The small intestine is narrow, and is stowed away in a

few irregular coils; the rectum is wide; a caecum is absent.

The CLOACA is peculiar. The coprodaeum and urodaeum, cf. p. 498, are

confluent, and form a wide, oval bag, closed in front and behind by strong

sphincters, and it acts normally as a urinary receptacle. In the dorsal

wall open the two ureters; a little towards the sides, and ventrally, open

the two oviducts, on the right and left, near the base of the clitoris.

Then follows a transverse, soft, muscular fold, which shuts off this cavity

from the proctodaeum or outermost chamber. In the latter is stowed away the

rather large copulatory organ. It arises out of the medio-ventral wall of

the cloaca, and has a deep, longitudinal groove on its morphologically

dorsal side for the conduction of the sperma, the vasa deferentia opening

near its basal end. On either side of the root of this organ, in both sexes

alike, opens a peritoneal canal, wide enough in large specimens to pass a

goose-quill. The outer opening of the cloaca forms a longitudinal slit;

within it, dorso-laterally, are the openings of the two anal musk-glands.

The KIDNEYS are much lobed. The testes are long and oval; the ovaries are

much elongated and flat; and the eggs contained therein in great numbers

are extremely small, except those which ripen during the time of

propagation.

The VASCULAR SYSTEM has attained the highest state of development of all

reptiles. The heart is practically quadrilocular, the partition between the

right and left ventricle being complete; but there is still a small

communication, the foramen Panizzae, which lies in the middle of the wall

common to both aortae, where they leave their respective ventricles. The

left aortic arch conveys all the arterialised blood out of the left

ventricle, and supplies head, neck, trunk, and tail. The right aortic arch,

coming from the right ventricle, supplies venous blood, mixed with what

little arterial blood it receives through the foramen Panizzae, to most of

the viscera. On a level with the stomach both descending aortic arches are

still connected with each other; the left aorta supplies most of the gut;

the right, the trunk and the kidneys.

The outer EAR lies in a recess, dorsally overhung by the lateral edge of

the bony squamoso-postfrontal bridge; and this {446}carries a flap of skin,

provided with muscles, to close the ear tightly. The tympanic membrane is

visible at the bottom of the recess; shining through it is part of that

cartilage which is homologous with the malleus of the auditory ossicular

chain; the outward extension of the latter on its way to the mandible,

behind the joint, passes as a partly cartilaginous string through the

slit-like hole which is visible at the back of the skull, between the

quadrate and the latero-occipital wing.

The EYES have, besides the lower and upper lid, a third, the nictitating

membrane, which can be drawn over the front of the eyeball. In the upper

lid lies a cup-shaped bony plate of variable size. The pupil contracts into

a vertical slit. The iris is greenish.

[Illustration: FIG. 104.–Map to illustrate the present distribution of

Crocodilia.]

The recent GEOGRAPHICAL DISTRIBUTION of the various kinds of Crocodilia

loses its mystery when we recollect that during the Tertiary period

Alligators, Crocodiles, and long-snouted Gavials existed in Europe. The

solitary species of Alligator in China is the last living reminder of their

former Periarctic distribution. The group, taken as a whole, is otherwise

now intertropical, Crocodiles alone inhabiting the Palaeo-tropical region,

together with long-snouted forms in the Oriental sub-region, while

Alligators and Caimans, with a few Crocodiles, live in America.

They are all rapacious, doing much damage by their predatory habits, and

are fierce and sulky in temper. But the danger to man differs much in

different countries. While Crocodiles are dreaded in some localities, they

are in others considered almost harmless, and men swim through the haunted

waters without hesitation. It seems as if certain old and wily individuals

turn into man-eaters, just like tigers and lions.

{447}Their home is the water, in which they pass the night, their time of

hunting. The prey is either patiently watched or stalked, and nothing falls

amiss. Water-birds are seized by the beast, which rises imperceptibly from

below. Some species are said to make use of their powerful tails for

hitting the victim and even jerking it into the mouth. The strength of

their jaws is enormous, and they do not let go what they have seized,

unless, in the case of a man, he has the presence of mind and the

opportunity to dig his fingers into the monster's eyes whilst being dragged

down.

In the morning they crawl on to sandbanks, or on to logs of wood, which

they closely resemble, in order to bask, mostly in such a position that on

the slightest alarm they can plunge into the water. For this reason they

frequently make a half circle before they settle down to rest, with the

heads turned towards the river. There they bask all day long, apparently

fast asleep, often with gaping mouths. But their sense of hearing and of

sight is sharp, and they learn from experience, old individuals being by

far the most wary. Commercially the skins are now of considerable value.

The flesh is white, and is tolerable eating but for the combination of

fishy and musky odour, which, although faint, is not to everybody's liking.

All the species have a voice, a kind of loud, short bark or croak, heard at

night and when angered. The female lays several dozen or even three score

white, oval, hard-shelled eggs in the sand, well out of the reach of

moisture; and some species construct an elaborate kind of nest. The mother

watches it, takes care of and fights for her offspring, numbers of which

fall an easy prey to large storks, fishes, and to the stronger members of

their own kind.

In the cooler countries they hibernate in the ground; and in hot countries,

which are subject to drought, some kinds aestivate in the hardened mud; or

they migrate. When during a prolonged drought on the island of Marajó, at

the mouth of the Amazon, the swamps and lakes were dried up, the Alligators

migrated towards the nearest rivers, and many perished in the attempt. On

one farm were found 8500 dead, and at the end of Lake Arary more than 4000.

Such occurrences in bygone times may perhaps explain the masses of bones

found here and there in a fossil state.

{448}The age to which Crocodiles can live is quite beyond calculation. They

are capable of propagation long before they are anything like half-grown,

maybe at an age of little more than ten years; then they continue to grow

perhaps for more than one hundred years, until they die.

It is customary to divide the Eusuchia, most of which are extinct, into a

longirostral and a brevirostral section. In the former the snout is much

elongated and narrow, and the nasal bones, although they are sometimes very

long, do not reach the nasal groove. The mandibular symphysis is very long,

and is formed not only by the dentary but also by the splenial bones. In

the brevirostral section the snout is shorter, sometimes broad and rounded

off, and the nasal bones are supposed to reach the nasal groove, or at

least to approach it very nearly; the mandibular symphysis is formed by the

dentaries only. But these distinctions are quite arbitrary, and there exist

all kinds of intermediate forms. For instance, in _Goniopholis_ and

_Diplocynodon_, which are both undoubtedly near allies of the recent

Crocodiles and Alligators, the nasal bones are considerably removed from

the nasal groove; and in _Crocodilus cataphractus_ they are separated even

from the premaxilla by the medio-dorsal suture of the maxillaries. Again,

in _Goniopholis_ the mandibular symphysis is so long that it comprises part

of the splenial bones. Both typically long- and short-snouted forms occur

already in the Upper Oolite, but in the Lower Jurassic age only

long-snouted kinds seem to have existed. The latter cannot easily be

connected with _Belodon_, one of the Parasuchia, on account of the position

of the nostrils; the mere shortening of the long premaxillaries of

_Belodon_ would not transfer its distinctly paired nostrils to the anterior

end of the premaxilla. To account for the position of the nasal groove in

the Eusuchia, we have to go back to a primitive condition, such as that of

the Pseudosuchian _Aëtosaurus_, and this consideration shows that the

Parasuchia and Eusuchia are collateral branches.

The Eusuchia have been split into many families. Zittel, for instance,

divides them into ten, some of them on insufficient grounds, since there

are too many intermediate forms; and more, sometimes quite unexpected,

modifications are still being found. Several of the accepted families

represent collateral or convergent lines of development.

{449}[Illustration: FIG. 105.–Group of Crocodiles. A long-snouted Gharial

or Gavial (_Gavialis gangeticus_) on the top of _Crocodilus acutus_; a Nile

Crocodile (_C. vulgaris_) in the foreground; _C. palustris_, a "Mugger," in

the right upper corner. Observe the peculiar floating attitude of the young

specimen.]

{450}There is the same tendency to transfer the choanae further back, owing

to the formation of a solid secondary roofing in of the mouth, to transform

the amphicoelous into procoelous vertebrae, to reduce the supratemporal

foramina, and to obtain a better development of the dorsal armour, whilst

that on the ventral side is gradually reduced. Lastly, there is a tendency

towards a shortening and broadening of the snout, a condition which has

reached its culmination in the Alligators, while the Gavials are survivals

of another branch. The notches in the premaxilla, for the reception of some

of the lower teeth, have also been acquired independently. Although the

recent Crocodilia cannot now, as has been pointed out by Boulenger, be

separated into different families, no valid diagnoses being possible owing

to the existence of _Tomistoma_, their phylogeny shows them to belong to at

least two heterogeneous groups.

KEY TO THE GENERA OF RECENT CROCODILIA.