THE DEVELOPMENT OF THE ALLIGATOR 226
BIBLIOGRAPHY 343
INDEX 349
ILLUSTRATIONS
PAGE
ALLIGATOR MISSISSIPPIENSIS. (In color.) _Frontispiece_
FIGURE
A. SKULL OF BELODON 5
1. MAP SHOWING THE PRESENT DISTRIBUTION OF CROCODILIA 6
2. HEADS OF AMERICAN ALLIGATOR AND CROCODILE _Facing_ 7
3. ALLIGATOR JOE IN THE EVERGLADES _Facing_ 10
4. ALLIGATOR HUNTER IN THE OKEFINOKEE _Facing_ 10
5. NEST OF C. POROSUS _Facing_ 21
6. JACKSON SLOUGH _Facing_ 21
7. A TYPICAL ALLIGATOR HOLE _Facing_ 23
8. ALLIGATOR NEST, MADE CHIEFLY OF GRASS _Facing_ 25
9. ALLIGATOR NEST, MADE CHIEFLY OF FLAGS _Facing_ 27
10. TWO SPECIES OF CAIMAN: BROAD-NOSED CAIMAN, SPECTACLED CAIMAN
_Facing_ 35
11. TWO AFRICAN CROCODILES: NILE CROCODILE, WEST AFRICAN CROCODILE
_Facing_ 39
12. SALT WATER CROCODILE _Facing_ 41
13. SKULL OF GAVIAL, VENTRAL VIEW _Facing_ 43
14. SKULL OF GAVIAL, LATERAL VIEW _Facing_ 43
15. ALLIGATOR SKINS _Facing_ 46
16. ENTIRE SKELETON OF CROCODILE 50
17. FIRST FOUR CERVICAL VERTEBRÆ OF CROCODILE 52
18. THORACIC AND SACRAL VERTEBRÆ OF CROCODILE 55
19. DORSAL VIEW OF SKULL OF ALLIGATOR _Facing_ 60
20. VENTRAL VIEW OF SKULL OF ALLIGATOR _Facing_ 63
20A. LONGITUDINAL SECTION OF TOOTH OF CROCODILE _Facing_ 66
21. LATERAL VIEW OF SKULL OF ALLIGATOR 69
22. POSTERIOR VIEW OF SKULL OF ALLIGATOR _Facing_ 70
23. SAGITTAL SECTION OF THE SKULL OF ALLIGATOR 71
24. DORSAL VIEW OF LOWER JAW OF ALLIGATOR _Facing_ 74
25. THE HYOID APPARATUS 77
26. THE STERNUM AND THE ASSOCIATED MEMBRANE BONES 79
27. THE PECTORAL GIRDLE AND ANTERIOR LIMB 82
28. THE PELVIS AND SACRUM 85
29. THE POSTERIOR LIMB 87
I. PLATE I. THE SHOULDER MUSCLES _Following_ 130
II. PLATE II. THE MUSCLES OF THE ANTERIOR REGION _Following_ 130
III. PLATE III. THE MUSCLES OF THE POSTERIOR REGION _Following_ 130
IV. PLATE IV. THE MUSCLES OF THE POSTERIOR REGION _Following_ 130
V. PLATE V. THE MUSCLES OF THE POSTERIOR REGION _Following_ 130
30. THE BRAIN OF THE ALLIGATOR _Facing_ 132
31. THE BRACHIAL PLEXUS OF C. ACUTUS 140
32. THE CRURAL PLEXUS OF A. MISSISSIPPIENSIS 142
33. INTERIOR OF THE MOUTH OF THE ALLIGATOR _Facing_ 151
34. THE DIGESTIVE SYSTEM OF THE ALLIGATOR 152
35. OUTLINE OF THE DIGESTIVE TRACT OF THE ALLIGATOR 158
36. COVERING OF THE ANTERIOR REGION OF THE TONGUE 160
37. COVERING OF THE POSTERIOR REGION OF THE TONGUE 161
38. GLAND FROM THE POSTERIOR REGION OF THE TONGUE 162
39. GLAND FROM THE POSTERIOR REGION OF THE TONGUE 164
40. COVERING OF THE ROOF OF THE MOUTH 166
41. TRANSSECTION OF THE ANTERIOR REGION OF THE ŒSOPHAGUS 169
42. TRANSSECTION OF THE POSTERIOR REGION OF THE ŒSOPHAGUS 170
43. EPITHELIUM OF ANTERIOR REGION OF ŒSOPHAGUS 172
44. EPITHELIUM OF ANTERIOR REGION OF ŒSOPHAGUS 173
45. TRANSSECTION OF WALL OF PYLORIC STOMACH 176
46. GLANDS OF FUNDUS OF STOMACH 177
47. TRANSSECTION OF WALL OF ANTERIOR REGION OF SMALL INTESTINE 181
48. TRANSSECTION OF WALL OF MIDDLE REGION OF SMALL INTESTINE 182
49. TRANSSECTION OF WALL OF POSTERIOR REGION OF SMALL INTESTINE 183
50. MUCOSA OF THE ANTERIOR REGION OF SMALL INTESTINE 184
51. TRANSSECTION OF THE WALL OF THE MIDDLE REGION OF THE SMALL
INTESTINE 185
52. TRANSSECTION OF THE WALL OF THE ANTERIOR REGION OF THE RECTUM 186
53. EPITHELIUM OF THE ANTERIOR REGION OF THE RECTUM 187
54. FEMALE UROGENITAL SYSTEM OF ALLIGATOR 193
55. MALE UROGENITAL SYSTEM OF ALLIGATOR _Facing_ 195
56. MALE ORGAN OF ALLIGATOR _Facing_ 195
57. RESPIRATORY ORGANS OF ALLIGATOR 198
58. HEART OF ALLIGATOR _Facing_ 202
59. VEINS OF THE POSTERIOR REGION OF ALLIGATOR 204
60. VEINS OF THE ANTERIOR REGION OF THE ALLIGATOR 209
61. ARTERIES OF THE POSTERIOR REGION OF THE ALLIGATOR 213
62. ARTERIES OF THE ANTERIOR REGION OF THE ALLIGATOR 215
VI.-XXVIII. PLATES VI TO XXVIII. A SERIES OF FIGURES TO ILLUSTRATE THE
DEVELOPMENT OF THE AMERICAN ALLIGATOR _Following_ 342
THE ALLIGATOR AND ITS ALLIES
CHAPTER I
THE BIOLOGY OF THE CROCODILIA
CLASSIFICATION
As in most groups of animals, there is considerable difference of
opinion as to the proper classification of the Crocodilia.
One of the older textbooks (Claus and Sedgwick) divides the order
Crocodilia into three sub-orders: the _Teleosauria_, _Steneosauria_,
and _Procœlia_, the last only being represented by living forms. The
Procœlia or Crocodilia proper are divided into three families,--the
_Crocodilidæ_, the _Alligatoridæ_ (including the caiman as well as the
alligator), and the _Gavialidæ_.
This division into families seems to be based mainly on the shape of
the head, or, at any rate, it throws those forms together that have
heads of the same outline.
It is this outline of the head that Ditmars (_Reptiles of the World_)
uses in classifying the Crocodilia, which, he says, are all included
in the single family--_Crocodilidæ_. The following list, taken from
his _Reptiles of the World_ (pp. 68-69), will give a clear idea of the
number, distribution, and maximum size of the members of the order
Crocodilia. More will be said of some of the members of this list later.
---------------------------------------------+----------------+-------
| _Habitat_ | _Max.
| | Size_
---------------------------------------------+----------------+-------
A. Snout extremely long and slender, | |
extending from the head like the handle of a | |
frying pan | |
_Gavialis gangeticus_, Indian Gavial |Northern India |30 ft.
_Tomistoma schlegeli_, Malayan Gavial |Borneo and |
|Sumatra |15 ft.
| |
B. Snout very sharp and slender; of | |
triangular outline | |
_Crocodilus cataphractus_, Sharp-nosed | |
Crocodile |W. Africa |12 ft.
_Crocodilus johnstoni_, Australian Crocodile |Australia |6-8 ft.
_Crocodilus intermedius_, Orinoco Crocodile |Venezuela |12 ft.
| |
C. Snout moderately sharp; outline distinctly| |
triangular | |
_Crocodilus americanus_, American Crocodile |Fla.; Mexico; |
|Central and S. |
|America |14 ft.
_Crocodilus siamensis_, Siamese Crocodile |Siam; Java |7 ft.
_Crocodilus niloticus_, Nile Crocodile |Africa generally|16 ft.
_Crocodilus porosus_, Salt-water Crocodile |India and |
|Malasia |20 ft.
| |
D. Snout more oval; bluntly triangular | |
_Crocodilus robustus_, Madagascar Crocodile |Madagascar |30 ft.
_Crocodilus rhombiferus_, Cuban Crocodile |Cuba only |7 ft.
_Crocodilus moreletti_, Guatemala Crocodile |Guatemala; |
|Honduras |7 ft.
| |
E. Snout short and broad; conformation | |
barely suggesting a triangular outline | |
_Crocodilus palustris_, Swamp Crocodile |India and |
|Malasia |12 ft.
_Osteolæmus tetrapis_, Broad-nosed Crocodile |W. Africa |6 ft.
| |
D′. Outline of head similar to that of | |
Section D | |
_Caiman trigonotus_, Rough-backed Caiman |Upper Amazon |6 ft.
_Caiman sclerops_, Spectacled Caiman |Central and S. |
|America |7-8 ft.
_Caiman palpebrosus_, Banded Caiman |Tropical South |
|America |7-8 ft.
| |
F. Snout very broad; bluntly rounded at tip | |
_Caiman latirostris_,[1] Round-nosed Caiman |Tropical South |
|America |7-8 ft.
_Caiman niger_,[2] Black Caiman |Tropical South |
|America |20 ft.
_Alligator mississippiensis_, American | |
Alligator |Southeastern |
|United States |16 ft.
_Alligator sinensis_, Chinese Alligator |China |6 ft.
---------------------------------------------+----------------+-------
[1] These species are exceptions in their genus. The snout is blunt
like that of the genus _Alligator_.
[2] Alleged to grow to this size by competent observers.
Gadow in the _Cambridge Natural History_ (p. 450) agrees with Boulanger
in believing that the recent Crocodilia cannot be separated into
different families, yet he describes seven families of Crocodilia, two
of which, the _Gavialidæ_ and _Crocodilidæ_, include the living members
of the order; the former includes the gavials, of course, and the
latter the crocodiles, alligators, and caimans.
Though “doctors disagree” thus in regard to the scientific
classification of this small group of animals, this fact does not in
the least diminish the intense interest in the individual members of
the order.
ANCESTRY
Although the huge dragon-like dinosaurs or “terrible reptiles,” some
of which were probably more than one hundred feet long, became extinct
during the Mesozoic epoch, perhaps millions of years before man made
his appearance upon earth, we have one group of reptiles still living
in certain parts of the earth of which the Mesozoic lords of creation
need not feel ashamed. While most of the living Crocodilia are mere
pigmies in size, compared to the Atlantosaurus, there are a few
representatives of the living group, to be discussed later, that are
said to reach a length of thirty feet, which length makes pigmies, in
turn, of most of the other living reptiles.
Considering the extinct as well as the living Crocodilia, Gadow says it
is very difficult to separate them from the Dinosauria. In the Mesozoic
Crocodilia the fore limbs were much shorter and weaker than the hind
limbs, as was often the case with the dinosaurs; they were almost
entirely marine, but gave indications of descent from terrestrial forms.
Various facts point, thinks Gadow, “to some Theropodous Dinosaurian
stock of which the Crocodilia may well form an aquatic, further
developed branch” (_Cambridge Natural History_, p. 432).
[Illustration:
Skull of =Belodon=. A, from above; B, from below. _A_, orbit; _Bo_,
basi-occipital; _Ch_, internal nares; _D_, pre-orbital fossa;
_Exo._ exoccipital; _Fr._ frontal; _Ju._ jugal; _La._ lacrymal;
_Mx._ maxilla; _Na._ nasal; _Pa._ parietal; _Pl._ palatine; _Pmx._
pre-maxilla; _Por._ post-orbital; _Prf._ pre-frontal; _Pt._
pterygoid; _Qu._ quadrate; _S_, lateral temporal fossa; _S′_,
superior temporal fossa; _Sq._ squamosal; _Vo._ vomer. (From Zittel.)
FIG. A. A TRIASSIC ANCESTOR OF THE CROCODILIA.
From Parker & Haswell, _Textbook of Zoölogy_.]
The direct ancestors of the Crocodilia, Gadow says, are still unknown.
GEOGRAPHICAL DISTRIBUTION
As will be seen by examination of the table (p. 2) from Ditmars, and
of Figure 1, the recent Crocodilia are found in all of the great
continental areas except Europe; mainly in the tropical or subtropical
regions.
[Illustration: FIG. 1. MAP SHOWING PRESENT DISTRIBUTION OF CROCODILIA.
(After Gadow.)]
The alligator is found in the southwestern United States and in China.
The crocodile is the most numerous in species and is the most widely
distributed of the group. It is especially characteristic of Africa and
Madagascar, but is found also in Florida, Mexico, Central and South
America, the West Indies, South Asia, the East Indies, and Australia.
The gavial is found in India and some of the islands of the Orient,
especially Borneo and Sumatra.
The caiman occurs in southern Mexico, Central and South America.
[Illustration: FIG. 2. HEADS OF AMERICAN ALLIGATOR AND AMERICAN
CROCODILE; ALLIGATOR ON LEFT. (After Ditmars.)
(Reproduced by Permission of Sturgis & Walton Co.)]
The distribution of individual forms will be mentioned again when they
are discussed in detail.
ALLIGATOR MISSISSIPPIENSIS
Since this animal, generally known as the American or the Florida
alligator (formerly _A. lucius_), is the one upon which most of the
facts of this book are based, it will be discussed first.
At this point it may be well to answer the question that is sure to be
asked by someone early in any conversation upon the Crocodilia. The
writer, and doubtless every other zoölogist, has been asked countless
times, “What is the difference between an alligator and a crocodile?”
As a matter of fact there is, perhaps, no absolute distinction between
the two groups, but there are certain features that make it easy to
distinguish, say, between the American alligator and the American
crocodile.
The most striking difference is in the outline of the head; the
alligator has a broad, rounded snout, while that of the crocodile
is narrower and more pointed (Fig. 2). Again, in the crocodile the
fourth tooth from the front projects slightly outwards and fits into
a notch in the side of the upper jaw, while in the alligator (also in
the caiman) the corresponding tooth on each side fits into a socket
in the upper jaw and hence is hidden, except in some old animals with
very long teeth, in which it may pierce the upper jaw and show from
above. According to Ditmars, the crocodile has, as a rule, larger and
more exposed teeth than the alligator. Finally, as will be brought out
later, the crocodile is usually more quick and active, and also more
vicious, than the alligator.
Very young alligators are nearly black, with distinct, yellow cross
bands; as they grow older these markings become less distinct until in
maturity the animals are of a uniform gray or dirty black color.
_Habitat._ The American alligator is found in the rivers and swamps of
the Southern States, from the southern part of North Carolina to the
Rio Grande, though Florida is usually thought of as being the region
in which they particularly abound. Years ago, before the rifle of the
ubiquitous tourist and so-called sportsman had gotten in its deadly
work, the alligators were probably very abundant in the Southern
States; but they have been so ruthlessly destroyed by native hunters
for their skins, and by others for mere wanton sport, that one may
travel, perhaps, for days along the rivers of the South without seeing
a single ’gator.
The account quoted by Clarke from Bartram’s travels of more than one
hundred years ago, while probably exaggerated, gives an idea of the
abundance of the alligators at that time: “The rivers at this place
from shore to shore, and perhaps near a half mile above and below
me, appeared to be one solid bank of fish of various kinds, pushing
through the narrow pass of San Juans into the little lake on their
return down the river, and the alligators were in such incredible
numbers, and so close together from shore to shore, that it would have
been easy to have walked across their heads, had the animals been
harmless.” At the present time it is usually necessary to travel far
from the usual routes of the Northern tourists to find alligators in
any abundance.
At Palm Beach, Florida, lived, a few years ago, and probably still
lives, a well-known hunter and guide, “Alligator Joe.” Just what
nationality he may be is difficult to determine, but that he knows
that trackless waste, the Everglades, at least in the region of Palm
Beach, is evident. He has an “alligator farm” near the great hotels
of that famous winter resort, at which he keeps, or did a few years
ago, a large number of alligators of all sizes, as well as a number
of crocodiles. For a consideration (by no means a modest one) he
would take out a party of tourists for a day into the Everglades,
guaranteeing that he would find an alligator for them to shoot. It was
rumored by the natives that an accomplice was always sent ahead to free
the alligator at the psychological moment, after the hunters had been
paddled by a devious course to the selected spot, but whether this were
true or not the writer was not able to determine. It is true, however,
that he and the writer paddled in a rather graceful canoe, dug out
of a single cypress log, and waded through the Everglades for several
days, searching for alligator eggs, and that we found only one nest and
saw only one or two alligators (Fig. 3).
Doubtless in more remote parts of the Everglades the alligators are
much more numerous.
During another summer the writer, with a guide, penetrated the very
center of the State, to the region southeast of Lake Kissimmee,
forty miles from the nearest railroad; here the alligators, and in
consequence their nests, are fairly abundant, though the native hunters
are, even in this remote region, rapidly thinning their ranks.
A still greater number of alligators was found, the following summer,
in the Okefinokee Swamp in southern Georgia. In the center of this
great waste, ten miles or more from dry land, nearly one hundred
alligators, ranging from about four to eight feet in length, were
killed within a week by a small party of native hunters with whom the
writer was traveling (Fig. 4).
Whether this wholesale destruction by sportsman and native hunter will
eventually exterminate our giant reptile, as has been the case with the
buffalo and other game animals, it is impossible to say. Unless the
Everglades and the Okefinokee are largely drained it seems probable
that a few alligators will always remain in the most inaccessible
regions.
[Illustration: FIG. 3. ALLIGATOR JOE IN THE EVERGLADES.
(From a Photograph by the Author.)]
[Illustration: FIG. 4. ALLIGATOR HUNTER IN THE OKEFINOKEE.
(From a Photograph by the Author.)]
The collection of eggs for sale and for hatching purposes, as well as
their destruction for food by bears and other animals, will also tend
towards the annihilation of the species in the course of time. The
economic importance of the alligator will be discussed later.
While in the old days, as has been said, the alligator was common in
the larger rivers and lakes, and may even have ventured short distances
into salt water, he must now frequently be satisfied to hide his great
body in a “’gator hole” that is scarcely more than a puddle. These
“holes” (Fig. 7) are common in central Florida and are sometimes
scarcely large enough to allow the alligator to dive into them to seek
the underground cave in which he hides. It is on the edge of such a
hole that the nest is built, as will be described later.
Often from a small swamp or slough alligator “trails” lead off in
different directions. These trails are narrow, winding gullies such as
might be made by cattle in a damp pasture. If followed from the main
slough the trail will usually be found to end in a “hole,” in which an
alligator will probably be found (Fig. 7). In a great swamp like the
Everglades or the Okefinokee such holes would naturally not be found.
On one side of the hole is usually a smooth place where the vegetation
is worn away; it is here that the ’gator “pulls out” to sleep in the
sun; and wary must the hunter be to approach within sight of the
animal before being seen or heard by him. At the first alarm he slides
quietly or plunges quickly into the muddy water, and the hunter must
wait long if he expects to see the ’gator come to the surface.
The opening of the cave is always below the surface of the water,
but it is possible that there may be a subterranean chamber that is
not completely filled with water. How the animal is gotten from his
cave will be described later. According to some writers the alligator
retires to his cave to hibernate during the cooler winter months. This
is possibly true in the more northerly limits of his range. It is
well known that if kept in cool water the alligator will lie dormant
and refuse all food for months at a time. The writer has had young
alligators in captivity, under these conditions, that refused food from
late in the autumn until nearly the first of April.
The proprietor of one of the largest alligator farms in the country
says: “Our alligators stop eating the first week in October and do not
begin to eat until the latter part of April. We have experimented with
our stock to see if we could get them to eat in the winter, and found
that by keeping the water in the tanks at a certain temperature they
would eat, but we found out that the warm water would make their bowels
move, and that they would not eat enough to keep themselves up, as in
the summer, and as a result they would become very poor and thin, so
we do not force them to eat any more.” The effect upon the growth of an
animal of these two methods of feeding will be noted later when the age
and rate of growth are discussed. The same writer says, in answer to
a question about hibernation: “In their wild state they go into their
dens under water and remain dormant all winter.” Whether this statement
is the result of actual observation the writer is not able to say, but,
judging by some other statements from the same source, it is probably
from hearsay. The writer, having visited the alligator haunts only in
late spring and summer, has had no opportunity of studying the habits
of the animal in its natural habitat during the winter season. During
the heat of summer the animal does not seek the sun as he is said to do
during cooler weather, but spends more time on the bank at night and
during the cooler parts of the day.
That he sometimes wanders over dry land, perhaps going from hole to
hole, is evident from the tracks that are sometimes seen crossing a
dusty road or path. These trails are easily recognized by the clawed
footprints with a line, made by the dragging tail, between them.
Although most awkward on land, he can, if necessary, move very quickly.
It is, however, in the water that he shows to best advantage; he is an
active, powerful swimmer, his tail being used as a propeller as in the
fishes. When swimming actively the legs are held close against the
body in order that they may retard the animal’s motion as little as
possible. While swimming in a leisurely way the top of the head is at
the surface of the water, perhaps just the nostrils and eyes projecting
above the surface, so that the size of the animal can be estimated by
the distance between these projecting points. One afternoon the writer
and a guide, while paddling along an old canal that was dug years ago
into the Okefinokee Swamp, were preceded for perhaps half a mile by a
large alligator that swam just fast enough to keep out of our reach
until he came to the place where he wanted to turn off into the swamp.
Although so awkward on land, the alligator is said to be able to defend
himself very effectively with his tail, which he sweeps from side to
side with sufficient force, in the case of a large specimen, to knock
a man off his feet. Although the writer has seen captured and helped
to capture alive several alligators up to eight feet in length he has
never seen this vigorous use of the tail as a weapon of defense.
While the alligator, like most other wild animals, will doubtless
defend itself when cornered, it will always flee from man if possible,
and the writer has frequently waded and swam in ponds and lakes where
alligators lived without the least fear of attack. This might not have
been possible years ago when the animals were more numerous and had not
been intimidated by man and his weapons.
_Food._ The food of the adult alligator consists of fishes, birds,
mammals, and possibly smaller individuals of its own species. The young
eat small fish, frogs, insects, or worms.
If the animal be too large to swallow whole it is shaken and torn, the
shaking being so vigorous that, according to Ditmars, the entrails of
the prey may be thrown to a distance of twenty feet or more. Should
two alligators seize the same prey at the same time they whirl about
in opposite directions so violently that the prey is torn apart. This
action may be illustrated by giving two small captive alligators a
piece of tough meat; they hold on with bulldog tenacity, and each,
folding its legs close to its body, will use its tail like a propeller
until the animal whirls around with remarkable speed. The commotion
that two ten-foot alligators would cause when thus struggling can
easily be imagined. That a large alligator, if it tried, could easily
drag under the water and drown a man or possibly a much larger animal
is evident.
While the alligator has a valve-like fold of skin in its throat that
enables it to open its mouth and crush its prey under water, it is said
that it must raise its head above water in order to swallow its food.
A young alligator on land will usually throw back its head when trying
to swallow a large piece of meat, so that it may be simply this motion
that brings the head of the alligator above the surface of the water.
Ditmars thus describes the fate of a dog that approached too near a
very large alligator: “As a dog, weighing about fifty pounds, unwarily
approached the edge of this creature’s tank, it was suddenly grasped
and before completing its first yelp of terror was dragged beneath the
surface. A few minutes later the twelve-foot saurian appeared at the
top, holding the dead canine in its jaws. The dog was shifted about,
amid the sound of breaking bones, and swallowed head first, and entire,
after a few gulps.”
_Size and Growth._ Although, years ago, alligators of fifteen feet
length may have been common in favorable localities in the South, it
is probable that few if any such monsters now exist. A twelve-foot
alligator, owing to its great girth, is a huge animal and but few of
this size are to be found in captivity. The largest specimen the writer
has ever seen is the one in the Bronx Zoo, which is barely thirteen
feet in length. At hatching the alligator is about eight inches in
length.
Clarke (17) says: “The largest specimen I saw measured twelve feet in
length; and none of the many hunters and natives of Florida I have met
have seen any longer than thirteen feet. All the hunters agree that it
is only the males that acquire the great size; no one had ever seen a
female that measured over eight feet, and the majority are not over
seven. The male has a heavier, more powerful head, and during the
breeding season especially is more brilliantly colored.”
It is a very common belief, even among those who should be most
familiar with their habits, that the growth of the alligator is
remarkably slow, so that a large specimen may be described by the
exhibitor as more than a century old. The same dealer in alligators
quoted above says upon this subject: “You can figure about two inches a
year to their growth.” He also says: “We judge that an alligator about
twenty-five to thirty years old will breed.” Even scientific writers
of reputation have not been free from this error in their writings.
That the alligator may live to an extreme age, as seems to be true of
some of the tortoises, is quite possible, and it is probable that after
reaching a length of twelve or fifteen feet the growth is very slow.
In captivity, when kept in warm water and other favorable conditions,
the alligator will grow, according to measurements taken at the New
York Zoölogical Park, at the rate of about one foot a year, for about
the first ten years. Under unfavorable conditions the growth may be
exceedingly slow. Under favorable conditions in nature the rate of
growth may exceed that given above.
Instead of requiring twenty-five to thirty years to reach sexual
maturity, as quoted above, it is likely that the female may lay eggs
at five to ten years, though such a fact is difficult to determine of
animals in their native haunts.
_Voice._ The alligator, unlike most other members of its class, the
_Ophidia_, _Chelonia_, and _Lacertilia_, has a voice, which, in
an adult bull, may be heard for a mile or more. This bellowing is
difficult to describe; it is something between a moan and a roar, and
may be to attract the opposite sex or to serve as a challenge to other
large animals. It is usually ascribed to the male, but whether confined
to him or not the writer is unable to say.
In younger animals the voice is, of course, less deep and in very young
individuals it is a squeak or grunt, easily imitated by hunters for the
purpose of luring the animals from their hiding places.
_Breeding Habits._ Judging from the statements of native hunters the
laying season of the alligator might be thought to be at any time from
January to September. As a matter of fact the month of June is the time
when most, if not all, of the eggs are laid. S. F. Clarke gives June
9th and June 17th as the limits of the laying season in Florida, but I
found at least one nest in which eggs were laid as late as June 26th:
no eggs were found before the first date given by Clarke. It seemed
quite certain that the laying, during the season in question, had been
delayed by an extreme drought that had dried up the smaller swamps
and reduced the alligator holes to mere puddles. Nests were found in
considerable numbers as early as June 8th, but no eggs were laid in
any of them until the end of the dry period which occurred nearly two
weeks later. Almost immediately after the occurrence of the rains that
filled up the swamps eggs were deposited in all of the nests at about
the same time. From the fact that all of these completed nests had
stood for so long a time without eggs, and from the fact that all of
the eggs from these nests contained embryos in a well-advanced state of
development, it seemed evident that the egg-laying had been delayed by
the unusually dry weather. Eggs taken directly from the oviducts of an
alligator that was killed at this time also contained embryos that had
already passed through the earlier stages of development. Thus it was
that the earliest stages of development were not obtained during this
summer.
It is said that during the mating season, which precedes by some time,
of course, the laying season, the males are noisy and quarrelsome,
and that they exhibit sexual characteristics of color by which they
may be distinguished from the females. Never having been in the
alligator country at this season, the writer has made no personal
observations along these lines, but from the frequency with which
alligators with mutilated or missing members are found it is evident
that fierce encounters must sometimes take place, whatever the cause.
During June and July, at least, and probably during most of the year,
the alligators are very silent, an occasional bellow during the very
early morning hours being the only audible evidence that one has
that the big reptiles are in the neighborhood. Whatever may be the
sexual differences during the mating season, at ordinary times the two
sexes are so much alike that I have, on more than one occasion, seen
experienced hunters disagree as to the supposed sex of an alligator
that had just been killed.
Although I have never seen a nest actually during the process of
construction, it is easy to imagine, after the examination of a large
number of freshly made nests, what the process must be like.
The alligator, probably the female, as the male, after the mating
season, takes no interest whatever in the propagation of his species,
selects a slight elevation on or near the bank of the “hole” in which
she lives. This elevation is generally, though not always, a sunny
spot, and is frequently at the foot of a small tree or clump of bushes.
Where the alligator is living in a large swamp she may have to go a
considerable distance to find a suitable location for her nest; when
her hole is scarcely more than a deep, overgrown puddle, as is often
the case in the less swampy regions, she may find a good nesting place
within a few feet of her cave. That the female alligator stays in the
neighborhood of her nest after she has filled it with eggs seems pretty
certain, but that she defends it from the attacks of other animals is
extremely doubtful: certainly man is in very little danger when he
robs the nest of the alligator, and, according to the statement of
reliable hunters, bears are very persistent searchers for and eaters of
alligator eggs. Having selected (with how much care it is impossible
to say) the location for the nest, the alligator proceeds to collect,
probably biting it off with her teeth, a great mass of whatever
vegetation happens to be most abundant in that immediate vicinity. This
mass of flags or of marsh grass is piled into a conical or rounded heap
and is packed down by the builder repeatedly crawling over it.
[Illustration: FIG. 5. A NEST OF C. POROSUS: PALAWAN, P. I.
(From a Photograph by Rowley.)]
[Illustration: FIG. 6.--JACKSON SLOUGH; NEAR LAKE KISSIMMEE, FLORIDA.
In the vicinity of this pond several alligator nests were found,
either within a few yards of the edge, or on the banks of smaller
“holes” which were connected with the larger pond by narrow “trails.”
(From a Photograph by the Author.)]
There is a great deal of variation in the size and form of the
different nests, some being two meters or more in diameter and nearly a
meter in height, while others are much smaller in diameter and so low
as to seem scarcely more than an accidental pile of dead vegetation.
It is probable that the nests are under construction for some time,
perhaps to give time for the fresh vegetation of which they are
composed to ferment and soften, and also for the material to settle
into a more compact mass. The compactness of the alligator’s nest was
well illustrated one day when the writer used an apparently deserted
nest as a vantage ground from which to take a photograph: on opening
this nest it was found, after all, to contain eggs, and though some
of the eggs were cracked, none of them were badly crushed. This nest
although it was so low and flat that it was thought to be one that had
been used during some previous season, contained forty-eight eggs, a
greater number than was found in any other nest; while in other nests
that were twice as large as this one were found less than half as many
eggs, showing that there is no relation between the size of the nest
and the number of eggs. The average number of eggs per nest, in the
twelve nests that were noted, was thirty-one. One observer reported a
nest that contained sixty eggs, but this, if true, was a very unusual
case. Reports of still larger numbers of eggs in one nest probably
refer to crocodiles, which are said to lay one hundred or more eggs in
a nest. Although crocodiles may be found in certain parts of Florida,
the writer has had no opportunity of observing their nesting habits.
The eggs are laid in the nest without any apparent arrangement. After
the nest has been prepared, and has had time to settle properly, the
alligator scrapes off the top, and lays the eggs in a hole in the damp,
decaying vegetation; the top of the nest is again rounded off, and it
is impossible to tell, without examination, whether the nest contains
eggs or not.
As to whether the same nest is used for more than one season there is a
difference of opinion among alligator hunters, and the writer has had
no opportunity of making personal observations.
[Illustration: FIG. 7. A TYPICAL ’GATOR “HOLE.”
Only a few yards across, and surrounded by a dense growth of
vegetation. On the far side is seen an opening in the surrounding
grass and flags where the ground is worn smooth by the alligator in
crawling out of the hole. Under the bank, probably near the place
where the alligator “pulls out,” is the deep cave into which the
inhabitant of this hole quickly goes on the approach of danger. As
this cave may be fifteen or twenty feet deep it is not an easy matter
to get the animal out. When a female alligator inhabits such a hole,
a nest may often be found within three or four yards of the water,
though it is sometimes at a greater distance. Such a hole as this may
be connected by narrow, winding “trails” with larger ponds, as noted
under Fig. 6. (From a Photograph by the Author.)]
While it is usually stated that the eggs are incubated by the heat
of the sun, it is held by some observers that the necessary heat is
derived not from the sun but from the decomposition of the vegetable
matter of which the nest is composed. Possibly heat may be derived
from both of these sources, but it seems likely that the conditions
that are especially favorable to normal incubation are moisture and
an even, though not necessarily an elevated, temperature. Moisture is
certainly a necessary condition, as the porous shell allows such rapid
evaporation that the egg is soon killed if allowed to dry. The inside
of the nest is always damp, no matter how dry the outside may become
under the scorching sun, so that this condition is fully met. The eggs
of the Madagascar crocodile, according to Voeltzkow,[3] offer a marked
contrast to those of the alligator. Instead of being laid in damp nests
of decaying vegetation, they are laid in holes that are dug in the dry
sand, and are very sensitive to moisture, the early stages, especially,
being soon killed by the least dampness. A crocodile’s nest containing
eggs is shown in Figure 5. In this species of crocodile, probably
_C. porosus_, the nest resembles that of the Florida alligator. The
photograph was taken by Mr. Rowley on the edge of a small lake on the
Island of Palawan, P. I.
[3] Voeltzkow, A., “The Biology and Development of the Outer Form of
the Madagascar Crocodile,” _Abhandl. Senckberg. Gesell._, Bd. 26, Hft.
I.
The daily range of temperature in the Southern swamps is sometimes
remarkably great, so that if the eggs were not protected in some way
they would often pass through a range of temperature of possibly fifty
degrees or more; while in the center of a great mass of damp vegetation
they are probably kept at a fairly constant temperature. Unfortunately
no thermometer was taken to the swamps, so that no records of the
temperatures of alligator nests were obtained, but it was frequently
noticed that when, at night or very early in the morning, the hand was
thrust deep into the center of an alligator’s nest the vegetation felt
decidedly warm, while in the middle of the day, when the surrounding
air was, perhaps, fifty degrees (Fahrenheit) warmer than it was just
before sunrise, the inside of the same nest felt quite cool. It is
probable, then, that the conditions of temperature and moisture in the
center of the nest are quite uniform. One lot of eggs that had been
sent from Florida to Maryland continued to incubate in an apparently
normal way when packed in a box of damp sawdust, the temperature of
which was about 80 degrees Fahrenheit. Another lot of eggs continued to
incubate, until several young alligators were hatched, in the ordinary
incubator, at a temperature of about 95 degrees Fahrenheit.[4]
[4] Reese, A. M., “Artificial Incubation of Alligator Eggs,” _Amer.
Nat._, March, 1901, pp. 193-195.
The fact that eggs taken directly from the oviducts of the cold-blooded
alligator contain embryos of considerable size seems to indicate that
no such elevation of temperature as is necessary with avian eggs is
necessary with the eggs of the alligator.
[Illustration: FIG. 8. A TYPICAL ALLIGATOR’S NEST, MADE CHIEFLY OF
GRASS.
The guide is feeling for eggs without disturbing the outside of the
nest. Being made of the same material as the background, the nest
does not stand out very sharply, though in nature the contrast is
somewhat more marked, owing to the fact that the surrounding grass is
green while the grass of which the nest is built is dead and brown.
(From a Photograph by the Author.)]
The complete process of incubation probably extends through a period
of about eight weeks, but no accurate observations along this line
could be made. For some hours previous to hatching the young alligators
make a curious squeaking sound inside the shell, that may be heard
for a distance of several yards: this sound may be for the purpose of
attracting the attention of the female alligator, who will open the top
of the nest in time to allow the just hatched alligators to escape:
unless thus rescued, it would seem impossible for the little animals
to dig their way out from the center of the closely packed mass of
decaying vegetation.
At the time of hatching the alligator is, as already noted, about eight
inches in length, and it seems impossible that it should have been
contained in so small an egg.
The size of alligator eggs, as might be expected, is subject to
considerable variation. In measuring the eggs a pair of brass calipers
was used, and the long and short diameters of more than four hundred
eggs were obtained. A number of eggs of average size, when weighed in
mass on the scales of a country store, gave an average of 2.8 oz. per
egg.
There was more variation in the long diameter of eggs than in the short
diameter.
The longest egg of all those measured was 85 mm.; the shortest was 65
mm. The widest egg (greatest short diameter) was 50 mm.; the narrowest
egg (least short diameter) was 38 mm.
The average long diameter was 73.742 mm.; the average short diameter
was 42.588 mm.
The greatest variation in long diameter in any one nest of eggs was
15.5 mm.; the greatest variation in short diameter in the eggs of any
one nest was 11 mm.
The average variation in the long diameter of the eggs from the same
nest was 11.318 mm.; the average variation in the short diameter of the
eggs from the same nest was 5.136 mm.
It will be seen from the above that the average variation in the long
diameter of eggs from the same nest is between one sixth and one
seventh of the long diameter of the average egg; while the average
variation in the short diameter of the eggs from the same nest is less
than one eighth of the short diameter of the average egg.
S. F. Clarke[5] gives the limits of the long diameter as 50 mm. and 90
mm., and the maximum and minimum short diameters as 45 mm. and 28 mm.
No such extremes in size were noticed among the eight hundred or more
eggs that were examined.
[5] _Journal of Morphology_, vol. v.
[Illustration: FIG. 9. AN ALLIGATOR’S NEST, SOMEWHAT SMALLER THAN THE
ONE REPRESENTED IN FIG. 8, BUILT CHIEFLY OF FLAGS.
The nest has been opened to show the irregularly arranged mass of
eggs inside. The size and shape of the egg are shown by the one in
the guide’s hand. (From a Photograph by the Author.)]
_Economic Importance._[6] More than one hundred years ago attempts
were made to utilize the skin of the alligator, but it was not until
about 1855 that these attempts were successful and alligator leather
became somewhat fashionable and some thousands of hides were converted
into leather. The demand was short-lived, however, and was not again
felt until the demand for shoe-leather during the war between the
States revived the business. At the close of the war the business
again failed, but about 1869 the demand became greater than ever and
has continued unabated to the present time. The supply of skins from
our own States proving inadequate, large numbers of skins were soon
imported from Mexico and Central America. The skins from South America
are so heavy that they are of little value in making leather. Of the
States of the Union, Florida has been the chief producer, the most
important centers for hides being Cocoa, Melbourne, Fort Pierce, Miami,
and Kissimmee. Ten men at the first-named place took, in 1899-1900,
2500 skins; one man took 800 skins in one year; another man collected
42 skins in one night. At Fort Pierce twelve men took 4000 skins in
1889. In 1899, three firms at Kissimmee handled 33,600 hides. After
this time the total number of hides taken and the average per man
diminished greatly.
[6] The following figures are from an article by C. H. Stevenson in the
Report of the Bureau of Fisheries, 1902, pp. 283-352.
Besides being killed for their hides, the alligators have been
destroyed by the thousands merely for wanton sport, so that in 1902 it
was estimated that their numbers in Florida and Louisiana were less
than one fifth of what they were twenty years before that time, and
unless steps be taken to prevent it, the alligator hide, as an article
of commerce, may cease to exist in our Southern States.
It has been claimed that the destruction of the alligator has allowed
the cane rat and muskrat to increase to a serious extent, the former
doing great damage to crops, the latter often injuring the levees to a
dangerous extent. Legislation to forbid the killing of alligators of
less than five feet in length has been suggested and should be passed,
since animals of less size have almost no commercial value for leather.
In 1902, the annual output from the tanneries of the United States
approximated 280,000 skins, worth about $420,000. Of these about
fifty-six per cent. came from Mexico and Central America, twenty-two
per cent. from Florida, twenty per cent. from Louisiana, and the
remaining two per cent. from the other Gulf States. South American
hides are not handled by the United States markets.
In 1908, there were marketed from the South Atlantic and Gulf States
372,000 pounds of alligator hides, valued at $61,000.
According to the United States Bureau of Fisheries the hunter in 1891
averaged about 60 cents for the skin, while in 1902 the price averaged
about 90 cents, varying between 15 cents and $2.00, depending on the
size and condition of the skin. “Prime hides five feet long, with no
cuts, scale slips, or other defects, are worth about 95 cents each, in
trade, when the hunter sells them at the country stores, and about
$1.10 cash, at the tanneries. Those measuring seven feet are worth
$1.55, six feet, $1.12; four feet, 52 cents, and three feet, 25 cents.
Little demand exists for those under three feet in length” (Report
Commissioner of Fish and Fisheries, 1902, p. 345). Hides of seven feet
are in most demand, those over ten feet are not much used. The income
of the hunters is largely increased by the sale of otter, bear, deer,
and other skins.
The different varieties of skins are described by Stevenson (74) as
follows:
“There are several distinct varieties of alligator skins on the
markets, the most important being the Floridian, Louisianian, and
Mexican; each differs from the others in certain well-defined
characteristics, and owing to these differences each variety has its
special uses.
“The Florida skins are longer in the body--that is, from the fore
legs to the hind legs--than those from Louisiana and Mexico, and
consequently they are largely in demand by manufacturers of large
handbags. They also have a number of so-called ‘buttons’ or ‘corn
marks’ on the inside or under surface of an equal number of the scutes
resulting from imbedded horn-like tissues in the center of those
scales. These increase the difficulty in tanning the skins and detract
somewhat from the appearance of the finished article, and for this
reason the Florida skins are ordinarily the cheapest on the market.
The farther south the skins are secured in Florida the greater the
number of ‘corn marks,’ and those from the vicinity of Key West are
almost valueless for this reason.
“The Louisiana skins differ from those of Florida in the absence of the
‘corn marks’ above noted, and from both the Florida and Mexican skins
in being more pliable and in having the scales more artistically curved
and shaped. Consequently they are preferred for such small articles as
card-cases and pocketbooks, and usually sell at the highest prices.
Skins obtained in Mississippi and Texas are similar to those secured
in Louisiana, while those from Georgia and South Carolina are similar
to those from Florida, except that the ‘corn markings’ are not so
numerous. All the Florida and Louisiana skins show greater uniformity
of coloring, being of a bluish black on the upper surface and a
peculiar bluish white on the under side.
“In addition to an absence of the characteristics above noted the
Mexican and Central American skins are distinguished by having from
one to four small dots or markings like pin holes near the caudal
end of each scale. The length of the Mexican skins varies greatly in
proportion to the width, sometimes equaling that of the Florida skins.
Those from the east coast of Mexico are the best, being lighter in
color and with neat and attractively shaped scales. The west coast
skins are yellowish in color when in the green state, and the scales
are larger and not so artistically formed. The Florida and Louisiana
skins are almost invariably split down the back, or rather along each
side of the back, so as to preserve the under side in a solid piece,
but most of the Mexican skins are split down the middle of the abdomen,
keeping the back intact, making what is commonly known as ‘horn
alligator.’ (See Fig. 15.)
“The skin should be removed soon after death as, in warm climates,
putrefaction sets in very early and the value of the skin is
depreciated. After removal, the flesh side of the skin is thoroughly
rubbed with fine salt, and the skin is carefully rolled up with
the salted side inside and is ready for shipment, but must be kept
in a dry, cool place. Great care must be taken not to cut the hide
since small cuts that are not noticeable in the raw skin may be so
conspicuous in the dressed skin as to render it of much less value; a
large percentage of the hides received in the markets are thus damaged.
“Formerly only the ‘belly skin’ was removed, by two longitudinal
incisions just below the horny portion of the back; but it was later
found that the thick horny skin of the back could be tanned nearly as
well as the thinner belly skin, so that the entire skin is now usually
removed by a longitudinal incision along the mid-ventral line, with
lateral incisions along each leg to the foot (Fig. 15). The entire
skin is more commonly taken in Mexico and Central America than in our
States.
“Although the raw skins are sold according to length, the tanned hides
are sold by the width of the leather at the widest part. Standard hides
sell for $1.00 to $1.65 per twelve inches of width. Some skins tanned
and dyed in a superior manner sell for $2.00 or more for single skins
of 2¹⁄₂ feet in length. As a rule the Louisiana skins fetch the highest
prices, and those from Florida the lowest. Imitation alligator leather
is now prepared in large quantities, principally from sheepskins or
the buffing from cowhides. These are tanned according to the usual
process, and before the skins are finished they are embossed with the
characteristic alligator markings by passing them between two rollers.”
(Above-mentioned report, p. 346.)
Very little of the leather is now used in making shoes, the chief
demand being for handbags, music-rolls, etc.
In hunting alligators for their hides two methods are usually employed,
in our Southern States at least. The common method is “fire-hunting”
at night; the hunters here go, either singly or in pairs, usually in
boats, sometimes on foot, with shotgun and torch. The torch may be
fastened to the hunter’s hat, after the manner of the miner’s lamp.
One more progressive hunter that I knew had, as a torch, an acetylene
lamp, attached to his hat, with the tube for the gas extending down
his back to the generator in his pocket. This lamp threw a blinding
beam of light far across the swamp into the eyes of the unsuspecting
’gator, which usually remained fascinated until it could be approached
to within easy range. A shotgun at close range, of course, blows off
nearly the entire top of the animal’s head and kills it instantly; it
is then seized before it sinks out of reach and is either taken into
the boat or dragged upon the bank to be collected with others in the
early morning.
In daylight, with no glaring light to hypnotize it, the alligator is
difficult to approach within range and it usually disappears into its
cave before the hunter can get a shot at it. The daylight hunter, then,
should be supplied not, of course, with a light, but with a ten- or
fifteen-foot pole with a large iron hook at the end. If the alligator
be vigorously prodded with this mammoth fishhook he will usually
finally seize it with his mouth and can be pulled out of his hole
alive. It is then an easy matter to kill him with a bullet through the
base of the brain. I have seen an eight-foot alligator thus killed with
a little .22 calibre “cat” rifle. An eight-foot alligator will often be
all that two men can manage to drag out of his cave in this way; and,
in the torrid heat of the Southern swamp, this violent exercise is not
to the liking of the usually not very energetic hunter.
While the manufacture of leather gives the chief value to the
alligator there are other ways in which it has some economic
importance. Chief of these is probably the sale of alligator goods to
tourists. In 1891 there were in Jacksonville, Florida, twelve dealers
in live and stuffed alligators. In 1890, 8400 alligators were sold to
tourists, the price for the live animals varying from $10.00 to $35
per hundred. For individual animals of the smallest size (less than
twelve inches long) the price is usually from 50 cents to $1.00. For
a three-foot alligator the price is generally $3-$5.00; for sizes
over three feet $2.00 per foot may be charged, though for very large
specimens the price may be from $50 to $300 each.
Besides the live and stuffed animals the teeth are polished and sold
as souvenirs; about 450 pounds of teeth were sold in 1890, at a price
varying from $1.00 to $2.00 per pound. From 75 to 200 teeth will make a
pound.
In 1891 about forty people, in addition to the regular dealers, were
engaged, in the United States, in stuffing alligators, polishing teeth,
etc. The teeth are extracted by burying the head until decomposition
sets in.
The tiny alligators that are most commonly sold to tourists, to be
brought North, perhaps, and allowed to freeze or starve to death, may
either be caught by a wire noose at the end of a fishing rod, or they
may be hatched from eggs that are taken from the nests shortly before
they are ready to hatch. Such eggs may readily be hatched by simply
keeping them moist and at a fairly constant temperature, as has been
previously noted. Besides the above uses Ditmars says: “The eggs are
eaten in many portions of the South, and the search for eggs at the
proper season furnishes profitable employment for many persons, as each
nest contains a large number of eggs.”
[Illustration: BROAD-NOSED CAIMAN. (_Caiman latirostris._)
Distribution: Tropical South America.
Attains a length of about seven feet. (After Ditmars.)
(Reproduced by Permission of Sturgis & Walton Co.)]
[Illustration: FIG. 10. SPECTACLED CAIMAN. (_Caiman sclerops._)
Tropical America.
The length of an adult is about eight feet. (After Ditmars.)
(Reproduced by Permission of Sturgis & Walton Co.)]
Never having eaten an alligator egg I cannot speak from personal
experience of its flavor; but it has always seemed strange to me that
more use is not made of the flesh of the alligator. This flesh is often
said to have too strong a flavor to be palatable; I have eaten it when
it had no such rank taste but was decidedly agreeable, being, as might
perhaps be expected of so amphibious an animal, somewhat like both fish
and flesh, yet not exactly like either. Perhaps greater care should
be taken in skinning an animal that is to be used for food in order
that the flesh be not tainted with the musk. It may be a lack of care
in preparation that has given rise to the impression that alligator
meat is too strong to be pleasant. It is perhaps, also, the “idea”
of eating a reptile that makes the meat unpopular. A half-grown boy,
who was once in the swamps with me, had expressed a great aversion
to alligator meat, so the guide, one day, offered him a nicely fried
piece of alligator meat, saying it was fish; the meat was eaten with
evident relish and the diner was not told until after a second piece
had disappeared what he had been eating. It always seemed strange to
me that the poor people of the South should not more often vary the
monotony of fat pork and corn bread with alligator steaks. Whether the
meat could be smoked or salted so that it would keep in a hot climate I
do not know; I am not aware of any experiments along this line.
THE CHINESE ALLIGATOR
Beside the American form, _Alligator mississippiensis_, the only other
species of alligator is found in China, along the Yang-tse-Kiang
River; it is _Alligator sinensis_. It reaches a length of six feet and
externally resembles its American relative; it is greenish black above
speckled with yellow; grayish below.
THE CAIMAN
This is the nearest relative of the alligator and is found in Central
America and tropical South America. As seen by the table on page 2, it
is usually a small animal, though one species, the black caiman, is
said to reach a length of twenty feet (Fig. 10). The nasal bones do not
form a bony septum as in the alligator and the ventral armor consists
of overlapping bony scutes. The canine teeth of the lower jaw fit into
a pit in the upper jaw, as in the alligator.
They are said by some writers to be extremely abundant in the waters
of the upper Amazon, migrating to the flooded forests during the rainy
season and returning to the streams on the approach of the dry season.
According to Ditmars there are five species of caiman of which the
spectacled caiman, _C. sclerops_, and the black caiman, _C. niger_, are
the most striking. The former is so named because of the spectacled
appearance due to the swollen and wrinkled upper eyelids; it reaches a
length of eight feet and is said to be of a treacherous disposition.
The latter has a blunt snout like the alligator and is the largest of
the New World crocodilians.
THE AMERICAN CROCODILE
Of about a dozen existing species of crocodile, but one, the American
crocodile, _C. americanus_, is found in the United States, and it is
limited to the swamps and coast of southern Florida below Lake Worth;
its greater sensitiveness to cold is doubtless the cause of its not
being found so far north as the alligator. Its range extends south
through Mexico and Central America into South America. It was first
found in Florida by Dr. Hornaday in 1875. It sometimes reaches a length
of fourteen feet.
As has already been noted there is, besides certain structural
differences, a marked difference in the dispositions of the Florida
alligator and crocodile. While an alligator may snap its jaws, hiss,
and swing its tail from side to side, it is not difficult for a couple
of men with ropes and a pole to safely tie up a large specimen. The
struggles of a crocodile are of a more serious nature. Ditmars thus
describes an encounter with a captive Florida crocodile: “The writer
well remembers his first acquaintance with a big fellow from Florida.
Driven out of the crate the crocodile looked the picture of good
nature. Standing away from what he thought to be the reach of his
tail, the writer prodded the apparently sluggish brute with a stick to
start it for the tank. Several things happened in quick order. With a
crescentic twist of the body utterly beyond the power of an alligator,
the brute dashed its tail at the writer, landing him such a powerful
blow that he was lifted completely from the ground. As he left _terra
firma_, an almost involuntary inclination caused him to hurl his
body away from a pair of widely-gaping, tooth-studded jaws swinging
perilously near. Landing with a thud on one shoulder, though otherwise
unhurt, the writer threw himself over and over, rolling from the
dangerous brute that was actually pursuing him on the run, body raised
high from the ground. For an instant it seemed as if the crocodile
would win. As the writer sprang to his feet and glanced backward, he
beheld the brute throw itself flat on its belly, open the jaws widely,
then remain motionless as a statue. Such is the average crocodile--an
active, vicious and, above all, treacherous brute.” Ditmars says again,
in the same book: “When the keepers of the reptile house of the New
York Zoölogical Park clean out the big pool of the crocodilians, they
actually walk over the backs of some of the big ’gators, so tame are
these. They never become unduly familiar with the crocodiles, finding
it necessary to pen the latter behind heavily barred gates--and in the
process the men are often chased from the enclosure.”
[Illustration: NILE CROCODILE. (_Crocodilus niloticus._)
Distribution: Africa generally; Madagascar.
Grows to a length of sixteen feet. (After Ditmars.)
(Reproduced by Permission of Sturgis & Walton Co.)]
[Illustration: FIG. 11. WEST AFRICAN CROCODILE. (_Crocodilus
cataphractus._)
Distribution: West Africa.
Does not attain so large a size as the Nile Crocodile. (After
Ditmars.)
(Reproduced by Permission of Sturgis & Walton Co.)]
In contrast to this ferocious aggressiveness in captivity the American
crocodile is said to be very timid and retiring when in its native
habitat.
Young animals are greenish with black marking; as they become older
they are of an olive color, and old specimens are dull gray.
THE ORINOCO CROCODILE, _C. intermedius_
This is a species with a very narrow snout that is not quite so large
as the preceding. It is said to be abundant in the Orinoco River and
its tributaries.
Besides the two above mentioned there is a small species, _C.
rhombifera_, found only in Cuba and hence known as the Cuban crocodile.
THE AFRICAN OR NILE CROCODILE, _C. niloticus_
This well known and much feared species is found throughout the
continent of Africa, and is very common on the island of Madagascar
(Fig. 11). In the lower waters of the Nile it is now nearly
exterminated. It has always been a conspicuous animal in Egypt and was
one of the animals held sacred by the Egyptians and preserved by them
as mummies. It is discussed by Herodotus, and the “leviathan” mentioned
in the Book of Job is doubtless this crocodile. In fact the name is
said to be derived from the ancient Greek for lizard, just as the
word alligator is said to be derived from the Spanish for lizard--_el
lagarto_; the resemblance in form between these big saurians and their
smaller relatives is evident. The alligator, being confined to America
and a small part of Asia, was probably not known to the ancients.
An excellent account of the development and habits of the present
species is given by Voeltzkow (78), who says it is, perhaps, the most
common vertebrate in Madagascar. The largest specimen measured by this
observer was thirteen feet; Ditmars gives sixteen feet as the maximum
size. This _man-eating_ crocodile, according to Ditmars, destroys more
human lives than any other wild animal of the dark continent.
The story told by Herodotus of the bird, probably a species of plover,
which enters the gaping mouth of the crocodile to pick off the leeches
found there may be true, since there is such a bird that may be seen
perching on the backs of crocodiles, and as the Crocodilia frequently
lie with their mouths wide open it is quite possible that these birds
may pick off the worms that are often found within. It is also possible
that the alertness of these birds to danger may serve as a warning to
the crocodiles with which they associate.
[Illustration: FIG. 12. SALT-WATER CROCODILE. (_Crocodilus porosus._)
Distribution: India to North Australia. Occurs at sea.
Grows to a length of twenty feet. (After Ditmars.)
(Reproduced by Permission of Sturgis & Walton Co.)]
According to Voeltzkow these crocodiles dig caves of thirty-nine to
forty feet length in the banks of the streams they inhabit, into which
they retire on the approach of danger. The caves open under water
and slope upward towards the surface of the ground where a few small
air-holes are found. The natives locate the caves by means of the
air-holes and dig out the hidden animal, first stopping up the entrance.
In Madagascar the eggs are laid in August and September and hatch in
about twelve weeks; they are laid at night, usually shortly before
daybreak. From twenty to thirty eggs are laid in one nest, which is
merely a hole dug in the dry sand. As was said in connection with the
Florida alligator, the habits of the two animals are quite different
in this respect,--the moisture that is so important in the one case is
fatal to the embryo in the other. When the eggs are laid the nest is
filled in with sand so that there is nothing to indicate its position
except that the female crocodile is in the habit of lying on the spot
where her eggs lie buried.
Like the alligator the young crocodile makes a squeaking noise shortly
before hatching and the mother doubtless opens the nest, at this time,
to allow the young to escape. A fence that Voeltzkow built around a
nest was repeatedly broken down by the mother in attempting to get back
to her eggs.
The character of the crocodile’s egg is discussed, in comparison with
that of the Florida alligator, on page 23.
THE MARSH CROCODILE OR MUGGER, _C. palustris_
Found in India, Ceylon, Burmah, the Malay Peninsula, and many of the
islands in that region. It has a rather broad snout, and reaches a
length of twelve feet. It is a timid form and is harmless to man. It is
frequently venerated by the Hindoos and is kept in a semi-domesticated
condition in ponds where it is fed and becomes very tame.
In the dry season when the natural ponds are empty they sometimes
migrate overland in search of water, but generally they bury themselves
in the mud and lie dormant until the rains begin again.
THE SALT-WATER CROCODILE, _C. porosus_
This is one of the largest if not the largest of living reptiles (Fig.
12). It is said by Ditmars to reach a length of twenty feet and there
is a record of one specimen that was thirty-three feet in length. It
is said to be easily recognized by the prominent, longitudinal ridge
that extends in front of each eye, over the prefrontal bone, and by the
absence of the suboccipital scutes.
[Illustration: FIG. 13. SKULL OF GAVIAL.
(Dorsal View.)
(Photograph from U. S. National Museum.)]
[Illustration: FIG. 14. SKULL OF GAVIAL.
(Lateral View.)
(Photograph from U. S. National Museum.)]
It is typically an inhabitant of tidal waters and is sometimes found
swimming at sea, out of sight of land; it seldom goes inland to any
great distance from the sea. It is a _man-eating_ species and many
human lives are said to be destroyed by it in India and surrounding
countries. A British “blue book” states that in British India 244
deaths were caused by Crocodilia in the year 1910.
In captivity it is savage and untamable. Ditmars, in speaking of three
specimens that he had in captivity, says they were “positively the most
vicious reptiles” he had ever seen.
THE INDIAN GAVIAL, _Gavialis gangeticus_
This animal, which inhabits the Ganges and other rivers of northern
India, is, with the possible exception of the preceding species, the
largest of the Crocodilia; it is said to reach a length of thirty feet,
which is twice that of a very large Florida alligator. As previously
noted its snout is extremely long and narrow (Figs. 13 and 14), with a
large, fleshy hump at the tip, that projects above the muddy water in
which the animal lies concealed.
It is a timid animal and, in spite of its huge size, dashes quickly
into the water on the approach of man, to whom it is seldom or never
dangerous. Its Indian name, _gharial_, from which its generic name has
been corrupted, means fish-eater, since its food consists, it is said,
largely if not entirely of fish.
Considering its huge size and the character of its jaws and teeth as
shown in Figures 13 and 14, it is fortunate that it prefers fish to
human flesh.
Anderson (2) describes the eggs and young of the Indian gavial. He
found forty eggs in a nest of sand; they were in two layers, with a
foot of sand between them. The young were 15.8 inches long at hatching.
He says: “The young run with amazing rapidity the moment they are out
of the shell.... Some of them actually bit my fingers before I had time
to remove the shell from their bodies.” The following quotation from
Oldenburg (46), for which I am indebted to Dr. Hussakof, is perhaps
the earliest reference to the egg of the American alligator. It also
mentions the habit that is practiced by some of the recent Crocodilia
of swallowing stones to aid in digestion, as was apparently done by
some of the large extinct reptiles.
“The eggs of _Crocodiles_ and _Alligators_ are little bigger than a
Turkey’s. I thought to bring one to England, but it was lost. I never
broke any to see the Yolk and White; but the Shell is as firme and
like in shape to a Turkey’s, but not spotted. I inquired into the
Stone in the Stomach of a _Cayman_ or _Crocodile_, and I found by the
inquiry of a very observing gentleman there, that they were nothing but
several Stones, which that Creature swallows for digestion. He took
out of one a piece of a Rock as big as his head: out of others he had
taken sixteen or twenty lesser. None regards them much there, whatever
_Monardes_ relateth.”
CHAPTER II
THE SKELETON
A. THE EXOSKELETON
The exoskeleton is well developed in the Crocodilia, and forms a very
considerable protection to its bearer. It is both dermal and epidermal
in origin.
The _epidermal skeleton_ of the alligator consists of oblong horny
scales, arranged in transverse rows; the long axes of the scales are
parallel to that of the body. On the tail, except along the mid-dorsal
line, and on the ventral side of the trunk and head these scales are
very regular in outline and arrangement; on the sides of the head
and trunk and on the legs they are much smaller and less regularly
arranged, while along the mid-dorsal line of the tail, especially in
its posterior half, they are elevated into tall keels that give the
tail a large surface for swimming. The first three digits of both manus
and pes are armed with horny claws, which also belong to the epidermal
part of the exoskeleton.
[Illustration: FIG. 15. ALLIGATOR SKINS; UNDER-SURFACE AND HORN-BACK.]
The _dermal exoskeleton_ consists of bony scutes that underlie the
epidermal scales of the dorsal surface of the trunk and anterior part
of the tail. The overlying scales, except in very young animals, are
always rubbed off, so that the bony scales are exposed. The ventral
or inner surface of the scutes is flat, while the outer surface is
strongly keeled and in old animals is often rough and pitted. The
plates are nearly square in outline and are closely joined together in
most places.
The scutes are grouped in two fairly distinct areas known as the nuchal
and the dorsal shields. The former lies just back of the head, in the
region of the fore legs, and consists of four larger and a number
of smaller plates (Fig. 15). The latter, or dorsal shield, extends
over the back in fairly regular longitudinal rows and quite regular
transverse rows. At the widest part of the trunk there are six or eight
of these scutes in one transverse row. They become smaller towards the
tail.
The _teeth_ are exoskeletal structures, partly of ectodermal, partly
of dermal origin. They are conical in shape, without roots, and are
replaced when lost. They will be described in connection with the skull.
Musk glands, said by Gadow to be present in all Crocodilia, are found
in both sexes and are derivations of the skin. One pair, each of which
may be as large as a walnut, is found on the lower side of the head,
one on the inside of each half of the mandible. The other pair is
inside of the lips of the cloaca.
_The Histology of the Integument._ To understand the structure of the
integument of the Crocodilia it is well to begin with the embryo. A
cross section of the epidermis of such an embryo will show the rete
Malpighii as a single layer of short, cylindrical cells; over these are
found more or less flattened, disk-shaped cells formed by transverse
division of the underlying cells of the rete. On the outside lies
the epitrichial layer which consists of a mosaic of polygonal cells,
near the middle of each of which lies an oval nucleus. Between the
epitrichial cells are small oval holes, not unlike the stomata in the
epidermis of plant tissues. Bronn thinks these are not artifacts, but
he does not suggest any explanation of their occurrence.
In the epidermis of young and half-grown animals the rete Malpighii
is seen still as above noted. On these cylindrical cells are found
flattened cells that gradually become very flat and lose their nuclei
as they pass over into the horny layer.
The stratum corneum consists of strongly flattened cells in which the
nuclei can no longer be clearly seen, though their location can usually
be determined by the groups of pigment granules. On the cells of the
more superficial layers of the stratum corneum are seen straight, dark
lines, perhaps ridges caused by pressure of the over- or underlying
polygonal cells. The individual cells of the horny layer are usually
easily isolated in the belly and neck regions where they never become
very thick; but in the back the cells in this layer are very numerous
and fuse with each other to form the bony plates; here the rete is the
only clearly differentiated layer. Whether prickle cells are present in
the epidermis of the crocodile Bronn is not certain, though he thinks
they probably are.
Rathke pointed out that on the surface of certain folds of the
integument, especially in the region of the jaws, are found in all
Crocodilia certain small, scattered, wart-like elevations, around
each of which is customarily a narrow, shallow, circular groove; they
usually have a dark brown but sometimes a gray or even white color.
Microscopic examination shows these warts to be of epidermal origin,
consisting of bright, round cells that are closely united, without
visible intercellular substance. Treatment with potassium hydroxid and
then with water will show sometimes, though not always, fine granular
nuclei in the cells.
In probably all members of the genus Crocodilus at least is found, on
the thick swelling on the right and on the left side of the neck and
trunk, a small, flat pit which has the appearance of the opening of
an integumental gland. The pits are present also in the scales of the
throat, under the side of the neck, sides of the body, lateral and
ventral surfaces of the anterior half of the tail, and the legs. They
are near the hinder border of the scales. Only occasionally are two
pits found in one scale. These pits are found in the gavials but are
absent in some, probably all, alligators. A small knob projects from
the center of some of the pits. These pits are not openings of glands
but have about the same structure as the pits seen in the head.
The integumental bones in the Crocodilia originate in the connective
tissue of the cutis. Investigations in young animals show that these
bones usually take their origin in the under and middle layers of the
cutis and generally work towards the periphery.
B. THE ENDOSKELETON
_I. The Vertebral Column._
[Illustration:
FIG. 16.--Skeleton of Crocodile. _D_, dorsal region; _L_, lumbar
region; _Sa_, sacral region; _Ri_, ribs; _Sc_, scapula; _H_, humerus:
_R_, radius; _U_, ulna; _Sta_, sternum abdominale: _Fe_, femur; _T_,
tibia; _J_, ischium; _C_, caudal vertebræ. (From Claus & Sedgwick.)]
The vertebral column consists of about sixty-five vertebræ, which
may be separated into the usual regions; there are nine cervical, ten
dorsal, five lumbar, two sacral, and about thirty-nine caudal. It is
likely that the number of caudals may be subject to frequent variation;
one complete skeleton had sixty-five vertebræ in all, another had
sixty-eight. A complete skeleton of the crocodile (species not known)
had sixty vertebræ. A thirteen-foot skeleton at Western Reserve
University had only sixty-one vertebræ, but some of the caudals were
evidently missing. Two skeletons of _C. porosus_ in the museum at
Singapore had sixty and sixty-three vertebræ respectively. A skeleton
of _Tomistoma schlegeli_ in the same museum had sixty vertebræ.
_The Cervical Vertebræ._ Since all of the cervical vertebræ bear ribs,
we shall assume the distinction between them and the dorsal vertebræ
to be that the ribs of the latter meet the sternum, while those of the
former do not reach to the sternum. Assuming this distinction, there
are, as was said above, nine cervical vertebræ.
[Illustration: FIG. 17. FIRST FOUR CERVICAL VERTEBRÆ OF A CROCODILE
(_C. vulgaris_). (From Reynolds, partly after Von Zittel.)
1. pro-atlas.
2. lateral portion of atlas.
3. odontoid process.
4. ventral portion of atlas.
5. neural spine of axis.
6. postzygapophysis of fourth vertebra.
7. tubercular portion of fourth cervical rib.
8. first cervical rib.
9. second cervical rib.
10. convex posterior surface of centrum of fourth vertebra.]
With the exception of the first two, to be discussed later, these are
all essentially alike and the fourth will be described as a type (Fig.
17). Its centrum is cylindrical or somewhat hourglass shaped, concave
anteriorly and convex posteriorly; it is not completely fused with the
neural arch but is united with it by sutures. From the anterior end
of the ventral surface of the centrum projects downward and forward
a small plow-shaped process, the hypapophysis. On each side of the
centrum, near its anterior end, is a facet with which the lower branch
(capitulum) of the rib articulates. The neural arch is strongly
developed and is extended dorsally into a prominent neural spine and
on each side as a short, blunt, transverse process with which the
tubercle or upper branch of the rib articulates. Posteriorly the arch
is notched on each side to form the openings for the exit of the spinal
nerves. Projecting dorsally and anteriorly from the arch are two short
processes which bear the medially and dorsally facing prezygapophyses
(Fig. 17). Just caudad to these processes are somewhat shorter
processes that bear the laterally and ventrally facing postzygapophyses
(Fig. 17, 6).
The _atlas_, as in other vertebrates, is highly specialized. It
consists (Fig. 17), even in the adult animal, six feet or more in
length, of four distinct portions, a ventral (4), a dorsal (1), and two
lateral (2) parts. The ventral portion is relatively more massive than
in most animals; its anterior surface is concave and forms the main
part of the articular surface for the occipital condyle of the skull.
Its postero-dorsal surface articulates with the odontoid process of the
axis. On its postero-lateral surfaces are the facets for articulation
with the first ribs, which, unlike the other cervical ribs, have but
one articular surface. Articulating dorsally with this ventral element
of the atlas are the two rather heavy lateral elements which form the
neural arch. Anteriorly they form the lateral parts of the articular
surface for the condyle and dorsally they unite for a short distance
with each other. Projecting ventrally from the posterior part of their
dorsal portion are the small postzygapophyses. Ventrally and laterally
they articulate with the odontoid process (Fig. 17, 3). Projecting
dorsad and cephalad from the dorsal surface of these lateral elements
is the dorsal element of the atlas (Fig. 17, 1), the pro-atlas, which
may not be properly a part of the vertebral column at all, since it is
said to be merely a membrane bone. Gadow says it is the detached neural
spine of the atlas. It is thin and triangular in shape, resembling in
contour a large, mammalian epiglottis. It forms an arch over the space
between the skull and the front of the atlas proper. Reynolds calls it
the pro-atlas.
_The Axis._ The centrum differs from those following it (described
above) mainly in its close articulation (not fusion) with the large
odontoid process; this process not only projects into the atlas,
as is usually the case, but articulates with its postero-lateral
border on each side, and is distinctly visible in a lateral view of
the neck (Fig. 17, 3). Like the rest of the cervical vertebræ the
posterior surface of the centrum is convex. The neural arch of the
atlas differs from those following mainly in having a much wider (in
an antero-posterior direction) neural spine. The lateral processes and
those bearing the prezygapophyses are also less strongly developed than
on the following vertebræ.
[Illustration: FIG. 18. ANTERIOR VIEW OF A, A LATE THORACIC AND B, THE
FIRST SACRAL VERTEBRA OF A YOUNG CROCODILE
(_C. palustris_). × ¹⁄₃. (After Reynolds.)
1. neural spine.
2. process bearing prezygapophysis.
3. facet for articulation with the capitulum of the rib.
4. sacral rib.
5. surface which is united with the ilium.
6. concave anterior face of centrum.]
_The Thoracic Vertebræ._ The first thoracic vertebra differs scarcely
at all from the ninth cervical; and the tenth thoracic differs from the
first lumbar only in bearing a short rib. Only the first three thoracic
centra bear the hypapophyses noted in connection with the cervical
vertebræ. The ribs of the first two thoracic vertebræ articulate with
them by two processes, as in the typical cervical vertebræ; the other
ribs articulate only with the transverse process. The fourth thoracic
may be described as a type of this region (Fig. 18, A). Its centrum
is rather longer than in the first two thoracic and in the cervical
vertebræ and has no process for articulation with the head of the rib,
otherwise it is essentially the same. Like all of the vertebræ behind
it and unlike those in front it is apparently completely fused with
its neural arch. The neural arch is very broad (in an antero-posterior
direction) and is extended dorsally as a wide neural spine (1). The
neural spines of the following thoracic and the first two or three
lumbar vertebræ are increasingly broad and truncated. The transverse
processes are very broad, long and thin, and in the third to eighth
vertebræ they have two articular surfaces, an anterior and more medial
one for articulation with the head of the rib (3) and a posterior and
more distal one for articulation with the tubercle of the rib. These
two surfaces approach each other as the vertebræ are followed caudad
until, in the last two thoracic vertebræ, they form practically one
surface. The processes of the pre- and postzygapophyses spring from
the arch at the base of the transverse process; the former surface is
directed dorsally and medially, the latter ventrally and laterally. The
intervertebral foramina are smaller and more nearly circular than in
the cervical region, and are more closely surrounded by bone.
_The Lumbar Vertebræ._ The five lumbar vertebræ are essentially like
the thoracic except that the transverse processes, which, of course,
bear no ribs, are both shorter and narrower. The postero-lateral border
of the centrum of the last of these five vertebræ has a small surface
for articulation with the antero-medial border of the transverse
process of the first sacral vertebra.
_The Sacral Vertebræ_ (Fig. 18, B). These are two in number. The
centrum of the first is concave in front and flat behind, instead of
being convex behind, and the second is flat (instead of concave) in
front, and convex behind. The neural spine and zygapophyses are as in
the lumbar region. Projecting laterally from each sacral vertebra,
forming a close, sutural joint with both centrum and neural arch, is a
heavy bone shaped like a truncated pyramid (4); the base of the pyramid
is ankylosed with the ilium. These bones seem to be much thickened
transverse processes, but since they are not completely fused with
their respective vertebræ and are said to ossify separately they should
probably be called sacral ribs. The two sacral vertebræ do not seem to
be any more closely united than are any other two vertebræ.
_The Caudal Vertebræ_ (Fig. 16, _C_). These are characterized by the
entire absence of ribs, and by the presence on all but the first
and the last four or five of V-shaped chevron bones. The first
ten or twelve of these chevron bones articulate chiefly with the
postero-ventral ends of the centra, but they also articulate with the
antero-ventral ends of the vertebra behind themselves; and as they are
followed caudad they seem to lie directly below the intervertebral
regions and to articulate equally with the vertebræ before and behind.
The chevron bones gradually diminish in size from before back. The
neural processes of the first four or five caudals are broad, like
those of the more anterior regions, but caudad to this point they
become narrower and more pointed, though they retain the same height
until about the last ten or twelve vertebræ. Towards the tip of the
tail the dorsal spines diminish in height and finally disappear. The
transverse processes of the first five or six of the caudals are long
and narrow. They gradually diminish in length until the eighteenth
caudal, back of which they are no longer to be seen. The zygapophyses
are mostly about the same as in the more anterior vertebræ, but towards
the posterior end of the tail the postzygapophyses come to lie between
rather than above the prezygapophyses. The neural canal diminishes,
of course, in size towards the tip of the tail until it is no longer
present, the last five or six vertebræ consisting only of the centra.
_II. The Skull._
The skull of the alligator is very massive and has several
peculiarities. 1. The bones of the dorsal surface are rough and
pitted, especially in old animals. 2. The jaws are enormously large in
proportion to the brain cavity, and are armed with many large teeth. 3.
The mandibular articulation is some distance caudad to the occipital
condyle. 4. The interorbital septum is mainly cartilaginous. 5. There
is a complicated system of Eustachian passages connecting with the back
of the mouth by a single opening. 6. The posterior nares are placed
very far back and the palate is correspondingly long.
The skull as a whole may be divided into three regions: the cranium,
the lower jaw, and the hyoid; these will be described in the order
given.
_The Cranium._ As a matter of convenience the bones will be described
as seen from the different aspects--dorsal, ventral, lateral,
posterior, and in sagittal section--without particular regard to their
grouping into segments or regions.
_The Dorsal Aspect_ (Fig. 19). At the extreme posterior end of the
median line lies the _parietal_ (23), double in the embryo but a
single bone in the adult. It forms a part of the roof of the cranial
cavity and articulates anteriorly with the frontal, laterally
with the postfrontals, squamosals, and, according to Reynolds,
with alisphenoids, pro-otics and epiotics, and ventrally with the
supraoccipital. It forms the median boundary of each of the two
_supratemporal fossæ_ (sf).
On each side of the parietal and forming the posterior comers of the
rectangular postero-dorsal region of the skull are the _squamosals_
(7). Each squamosal articulates medially with the parietal, anteriorly
with the postfrontal, and ventrally with the quadrate and exoccipital.
It forms part of the posterior and lateral boundaries of the
supratemporal fossa and a part of the roof of the external auditory
meatus.
Articulating with the anterior border of the squamosals and forming
the anterior corners of the rectangular region mentioned above are
the _postfrontals_ (6). The postfrontal articulates medially with the
parietal and frontal, and ventrally with the alisphenoid and a small
part of the quadrate. It sends, in a ventro-lateral direction, a thick
process that unites with a similar process from the jugal to form
the _postorbital bar_ (pb) which lies between the orbit (o) and the
temporal fossa (tf). The postfrontal forms the antero-lateral boundary
of the supratemporal fossa.
Articulating posteriorly and laterally with the parietal and the
postfrontals, and forming the highest point of the skull, is the single
_frontal_ bone (24), which, like the parietal, is paired in the embryo.
It is a heavy bone whose dorsal surface is flattened posteriorly,
deeply concave in the middle region, and drawn out into a long
projection anteriorly. It forms part of the roof of the cranial cavity
and articulates ventro-laterally with the alisphenoid and anteriorly
with the prefrontals and nasals. It forms a part of the median boundary
of the orbit.
The _prefrontal_ (4) is an elongated bone in the latero-median border
of the orbit. Medially and anteriorly it articulates with the frontal
and nasal, laterally with the maxillary and lachrymal, and ventrally,
by a heavy process, with the pterygoid.
[Illustration: FIG. 19. DORSAL VIEW OF THE SKULL OF THE ALLIGATOR (_A.
Mississippiensis_).
1. premaxilla.
2. maxilla.
3. lachrymal.
4. prefrontal.
5. jugal.
6. postfrontal.
7. squamosal.
8. quadrate.
12. quadratojugal.
23. parietal.
24. frontal.
25. nasal. _an_, anterior nares; _o_, orbit; _pb_, postorbital bar;
_sf_, supratemporal fossa; _tf_, lateral temporal fossa.]
The _nasal_ (25) is a long narrow bone forming the greater part of
the roof of the nasal passage. Along the median line of the skull it
articulates with its fellow; posteriorly with the frontal; laterally
with the prefrontal and maxillary; and anteriorly with the premaxilla.
In the crocodile, caiman, and gavial it also articulates with the
lachrymal. In the alligator the anterior ends of the two nasals form a
narrow rod of bone that extends across the anterior nares, and, meeting
a projection from the premaxillaries, divides the opening into right
and left halves. In the crocodile the nasals project only a very little
way into the nares; in the caiman (according to Reynolds) they do not
extend into the nares at all, and in the gavial, whose much elongated
snout is mainly due to the great length of the maxillaries, the nasals
do not extend more than a third of the distance from the prefrontals to
the anterior nares.
The _maxilla_ (2) is a large bone that forms a large part of the upper
jaw and that holds most of the teeth of that jaw. On the ventral
side, as will be described later, it articulates with its fellow in
the middle line, with the premaxilla, with the palatine, and with
the transpalatine. Dorsally it articulates with the premaxilla in
front; with the nasal and prefrontal on the medial side; and with the
lachrymal and jugal behind.
The _premaxilla_ (1) forms, with its fellow, the extreme tip of the
upper jaw. Each bone forms the anterior and lateral borders of its half
of the anterior nares. It articulates medially with its fellow and
posteriorly with the nasal and maxilla. Ventrally, as will be noted
later, it bears five teeth and articulates with its fellow medially and
with the maxilla posteriorly. Between the premaxillæ on the ventral
side is the large anterior palatine foramen.
The _lachrymal_ (3) is a fairly large bone that forms the anterior
border of the orbit. It is bounded laterally by the jugal, anteriorly
by the maxilla, and medially by the prefrontals. Its postero-medial
border is pierced by a large lachrymal foramen that extends lengthwise
through the bone and opens, at its anterior end, into the nasal chamber.
The _supraorbital_, missing in the skull figured, is a small bone lying
in the eyelid close to the junction of the frontal and prefrontal.
Being unattached it is usually absent from prepared skulls.
The _jugal_ or _malar_ (5) is an elongated bone that forms a part
of the lateral border of the head, on the one hand, and most
of the lateral border of the orbit on the other. Anteriorly it
articulates with the maxilla; medially with the lachrymal and
prefrontal; posteriorly with the quadratojugal, and ventrally with
the transpalatine. With the transpalatine it sends, in a dorso-medial
direction, a process that meets the process, described above in
connection with the postfrontal, to form the postorbital bar.
The _quadratojugal_ (12) is a small bone, wedged in between the jugal
in front and the quadrate behind.
[Illustration: FIG. 20. VENTRAL VIEW OF THE SKULL OF THE ALLIGATOR (_A.
Mississippiensis_).
2. maxilla.
5. jugal.
8. quadrate.
9. palatine.
10. pterygoid.
11. transpalatine.
12. quadratojugal.
14. basioccipital. _a_, anterior palatine vacuity; _eu_, opening of
the median Eustachian canal; _pn_, posterior nares; _pv_,
posterior palatine vacuity.]
The _quadrate_ (8) is more irregular and has more complicated
articulations than almost any bone in the skull. Its posterior end,
which forms the articular surface for the lower jaw, is elongated
laterally and slightly concave. Anteriorly the quadrate articulates
with the quadratojugal; medially with the basisphenoid and exoccipital;
dorsally with the exoccipital, squamosal, postfrontal, and, possibly,
with the pro-otic; ventrally with the pterygoid, alisphenoid, and
probably with some of the otic bones. Its dorsal side forms most of
the floor of the external auditory meatus which will be described
later. While the basioccipital may be seen from the dorsal side, it is
not really one of the dorsal bones of the skull and will be described
later; the same is true of the pterygoids and palatines which may be
seen through the empty orbits.
_The Ventral Aspect_ (Fig. 20). The larger part of this side of the
skull is made up of four pairs of bones: the premaxillæ, the maxillæ,
the palatines, and the pterygoids, lying, from anterior to posterior,
in the order named.
The _premaxilla_ (1), as described in the dorsal view of the skull, is
a triangular bone which, with its fellow, forms the anterior end of
the snout. Each premaxilla bears five teeth, not only in the alligator
but in the crocodile, the caiman, and in the gavial. Of these teeth
the fourth from the front is the largest; the first two are small,
and the third and fifth are of intermediate size. This arrangement as
to size is also true, apparently, in the other groups of Crocodilia.
The ventral surface of the premaxilla, which is more or less flat and
horizontal, is pierced by a number of small foramina, in a row parallel
to the curved outer margin of the bone. Between these foramina and the
base of the teeth are four rounded depressions to receive the points of
the first four teeth in the lower jaw; of these depressions the first
and fourth are the deepest. The first pit often becomes so deep as to
perforate the bone; this is true also with the crocodile and, according
to Reynolds, with the caiman, but is not true of the gavial, whose
interlocking teeth project outside of the jaws. It will be remembered
that one of the chief distinctions, given early in this work, between
the crocodile and the alligator is that in the former the fourth tooth
in the lower jaw fits into a notch and not into a pit in the upper jaw.
The _maxilla_ (2), which with its fellow forms most of the hard palate,
has also been mentioned in connection with the dorsal aspect. Each
maxilla is notched, posteriorly, to form the anterior border of the
posterior palatine vacuity, and together they are notched to receive
the rectangular anterior ends of the palatines. The postero-lateral
extremity of the maxilla articulates with the transpalatine. Along the
outer border of the bone are the teeth, of which there are fifteen or
sixteen in the alligator, about the same number (perhaps one or two
less) in the caiman and crocodile, and about twenty-four in the gavial.
The first or anterior eight or ten teeth have individual sockets, the
rest are placed in a groove. In the crocodile none of the teeth have
individual sockets, and in the gavial they all have sockets. The
premaxillary and more anterior of the maxillary teeth are slightly
recurved and are sharper than the posterior maxillaries which besides
being blunt have a constriction above the surface of the socket.
The crocodilian tooth consists of three layers (Fig. 20 A).
The enamel (e) forms a fairly thick layer over the crown of the tooth;
it exhibits a very clear striated structure, the striations being
apparently due to stratification.
Some of the tubules of the dentine (d) continue into the enamel, where
they may be distinguished by their remarkable fineness and their
straight course.
The cement (c) covers the root of the tooth that projects into the
alveolus of the jawbone; it is much more strongly developed than in
the lizards and contains a very large number of bone corpuscles which
are distinguished from the bone corpuscles proper by their greater
circumference.
The fairly large pulp cavity (p) has, like the tooth itself, a conical
form.
Parallel to the teeth is a row of small foramina, a continuation of
those noted in the premaxilla; some or all of these foramina open
into a longitudinal sinus along the alveolar border of the maxilla;
this sinus opens posteriorly by one or more large apertures into the
posterior palatine vacuity.
The _palatines_ (9) form a broad bar of bone from the pterygoids
behind to the maxillæ in front. They are united with each other by a
straight median suture and form a considerable part of the floor as
well as a part of the side walls and roof of the nasal passage. They
form most of the median boundaries of the posterior palatine vacuities
(pv). Dorsally they articulate with the pterygoids, prefrontals, and
vomers.
The _pterygoids_ (10) are the very irregular bones that project ventrad
and caudad from beneath the orbits. Their suture is continuous, caudad,
with that between the palatines and at the posterior end of this
suture is the posterior opening of the nasal chamber, the posterior
nares (pn). This opening is divided by a vertical, longitudinal, bony
septum, and the part of the chamber into which it immediately opens,
which lies in the pterygoids, is divided by a number of transverse,
vertical septa. Posterior and dorsal to the posterior nares the
pterygoids are fused. Anteriorly the pterygoids articulate with the
palatines; dorsally with the quadrates, basisphenoid, alisphenoids, and
prefrontals, and dorso-laterally with the transpalatines. The lateral
vertical border of the pterygoid is roughened and is, according to
Reynolds, covered, during life, with a pad of cartilage against which
the medial side of the mandible plays.
The _transpalatine_ (11) is a T-shaped bone articulating ventrally
with the pterygoid and dorsally with the maxilla, the jugal, and the
postfrontal.
[Illustration: FIG. 20A. LONGITUDINAL SECTION OF THE JAW AND TOOTH OF A
CROCODILE.
(After Bronn.)
_c_, cement; _d_, dentine; _e_, enamel; _p_, pulp, of functional
tooth; _c′_, cement; _d′_, dentine; _e′_, enamel, of rudimentary
tooth; _e″_, epidermis; _k_, bone of jaw.]
The _basioccipital_ (14) is seen projecting caudad as the single
occipital condyle; it will be described in connection with the
posterior aspect of the skull.
The _jugal_ (5), _quadratojugal_ (12), and _quadrate_ (8) may all be
seen from this view. The first two have been sufficiently described in
connection with the dorsal aspect; the last will be further described
in connection with the lateral aspect.
Just caudad to the posterior nares is a small opening, the unpaired
Eustachian canal (eu).
_The Lateral Aspect_ (Fig. 21). As will be seen by the figure,
practically all of the bones visible in this view have already been
described, except those of the mandible, which will be described
separately. At the base of the skull are, however, two bones, the basi-
and alisphenoid, that have not been described and that show as well
in this as in any other view. The _basisphenoid_ (just below v and
hidden by the pterygoid) was mentioned in connection with the quadrate,
with whose posterior margin it articulates. It is an unpaired bone
of very irregular shape. Anteriorly it is flattened out to form the
rostrum, a rectangular process that forms the posterior part of the
interorbital septum; in fact it is the only part of the septum present
in a prepared skull, since the rest is cartilaginous. Dorso-laterally
the basisphenoid articulates with the alisphenoid; posteriorly with
the basioccipital; ventrally with the pterygoid; and posteriorly with
the exoccipital and basioccipital. On the dorsal surface of the
basisphenoid is the pituitary fossa, not seen, of course, in this view
of the skull.
The _alisphenoids_ (crossed by the dotted line from V) are a pair of
very irregular bones that form most of the antero-lateral walls of
the brain case. They articulate dorsally with the parietal, frontal,
and postfrontal; ventrally with the basisphenoid and pterygoid; and
posteriorly with the quadrate and some of the otic bones not visible in
this view. Between it and the quadrate, plainly visible in this view,
is a large opening, the _foramen ovale_ (V), through which, according
to Reynolds, the trigeminal nerve passes. In the middle line, directly
under the frontal bone, is an opening between the anterior wings of
the two alisphenoids, for the exit of the optic nerves. Ventrad and
caudad to this opening, and sometimes continuous with it, is another
large foramen, just dorsad to the rostrum, for the exit, according to
Reynolds, of the oculomotor and abducens nerves. Projecting caudad
is seen the rounded condylar part of the _basi-occipital_ (14) to
be described later, and dorso-cephalad to this is a part of the
exoccipital (13) in which four foramina may be seen; of the dorsal
three the one nearest the condyle and foramen magnum is for the exit
(Reynolds) of the hypoglossal nerve (XII); slightly dorso-cephalad to
this is one for the vagus nerve (X); between these two is a very small
one for a vein; the largest and ventrally located foramen is for the
entrance of the internal carotid (15). Another large foramen in the
exoccipital bone will be seen and described in connection with the
posterior view of the skull. Dorsal to the quadrate and largely bounded
by it is the wide _external auditory meatus_ (16), which leads into the
tympanic cavity. This cavity is complicated by a number of canals that
lead from it in various directions. Overhanging the cavity and meatus
is the squamosal bone, described in connection with the dorsal aspect
of the skull.
[Illustration: FIG. 21. LATERAL VIEW OF THE SKULL OF AN ALLIGATOR
(_Caiman latirostris_). ×¹⁄₃. (Brit. Mus.)
(After Reynolds.)
1. premaxilla.
2. maxilla.
3. lachrymal.
4. prefrontal.
5. jugal.
6. postfrontal.
7. squamosal.
8. quadrate.
9. palatine.
10. pterygoid.
11. transpalatine.
12. quadratojugal.
13. exoccipital.
14. basi-occipital.
15. foramen by which carotid artery enters skull.
16. external auditory meatus.
17. frontal.
18. supra-angular.
19. articular.
20. dentary.
21. coronoid.
22. angular.
III, VI, opening for exit of oculomotor and abducens nerves.
V, foramen ovale.
X, pneumogastric foramen.
XII, hypoglossal foramen.]
_The Posterior Aspect_ (Fig. 22). Most of the bones seen in this
view have already been described. The _pterygoids_ (10) form the two
prominent, ventro-lateral projections, while dorsal to these is the
large process formed by the quadrate (8) and quadratojugal (12). The
dorsal margin is formed by the edges of the parietal (23) and the
squamosals (7). Immediately below the parietal is the supraoccipital
(26); it is a small, triangular bone, articulating above with the
parietal and squamosals, below with the exoccipitals, and anteriorly
with the epiotic. It takes no part in the formation of the foramen
magnum.
The _exoccipitals_ (13) form the entire boundary of the foramen
magnum except the narrow ventral portion formed by the basioccipital.
Each exoccipital is a wing-shaped bone, articulating dorsally with
the squamosal and supraoccipital, ventrally with the quadrate,
basioccipital, and basisphenoid, and anteriorly with the opisthotic. It
is pierced by five foramina, four of which were described in connection
with the lateral view. Some distance laterad and somewhat dorsad to
the pair already described is the fifth and largest foramen (VII); it
really lies between the exoccipital and quadrate, but the former bone
forms almost its entire boundary; through it, according to Reynolds,
pass the seventh nerve and certain blood-vessels.
[Illustration: FIG. 22. POSTERIOR VIEW OF THE SKULL OF A.
MISSISSIPPIENSIS.
7. squamosal.
8. quadrate.
10. pterygoid.
11. transpalatine.
12. quadratojugal.
13. exoccipital.
14. basioccipital.
15. foramen for carotid artery.
23. parietal.
26. supraoccipital.
VII. foramen for 7th nerve and certain blood-vessels. _bs_, position
of basisphenoid.]
[Illustration: FIG. 23. LONGITUDINAL SECTION THROUGH THE SKULL OF AN
ALLIGATOR (_Caiman latirostris_). ×¹⁄₃. (Brit. Mus.) (After Reynolds.)
1. premaxilla.
2. nasal.
3. frontal.
4. parietal.
5. supra-occipital.
6. epiotic.
7. prootic.
Immediately in front of the figure 7 is the prominent foramen for
the trigeminal nerve.
8. opisthotic.
9. basioccipital.
10. quadrate.
11. pterygoid.
12. basisphenoid.
13. alisphenoid.
14. prefrontal.
15. vomer.
16. maxilla.
17. palatine.
18. dentary.
19. splenial.
20. angular.
21. supra-angular.
22. articular.
23. coronoid.
24. exoccipital.
25. squamosal.
26. jugal.
27. external mandibular foramen.
28. internal mandibular foramen.
VIII. internal auditory meatus.
XII. hypoglossal foramen.]
[Illustration: FIG. 24. DORSAL VIEW OF LOWER JAW OF ALLIGATOR (_A.
Mississippiensis_).
18. dentary.
19. splenial.
21. supra-angular.
22. articular.
23. coronoid.]
The _basioccipital_ (14) which, as has been said, forms a small part
of the ventral wall of the foramen magnum, consists of a heavy dorsal
portion, the ventrally curved condyle, and of a broader, irregular
ventral portion, between which and the basisphenoid is the single
opening of the Eustachian canals (eu). Dorsally and laterally the
basioccipital articulates with the exoccipitals; ventrally, laterally,
and anteriorly with the basisphenoid which was described in the lateral
view.
_The Sagittal Section_ (Fig. 23). The only bones shown in this figure
(besides those of the mandible, to be described later) that have
not already been described are the vomers and those of the auditory
capsules.
The _vomers_ (15) are delicate bones articulating with the maxillæ, the
palatines, the pterygoids, and with each other. They form a part of the
septum and roof of the nasal passage.
The _mesethmoid_ is not ossified.
Reynolds describes the bones of the auditory capsules as follows:
“Three bones, the _epiotic_, _opisthotic_, and _pro-otic_, together
form the auditory or _periotic_ capsule of each side. They are wedged
in between the lateral portions of the occipital and parietal segments
and complete the cranial wall in this region. Their relations to the
surrounding structures are very complicated, and many points can be
made out only in sections of the skull passing right through the
periotic capsule. The relative position of the three bones is, however,
well seen in a median longitudinal section. The _opisthotic_ early
becomes united with the exoccipital, while the _epiotic_ similarly
becomes united with the supraoccipital, the pro-otic (Fig. 23, 7)--seen
in longitudinal section to be pierced by the prominent _trigeminal
foramen_--alone remaining distinct throughout life. The three bones
together surround the essential organ of hearing which communicates
laterally with the deep tympanic cavity by the _fenestra ovalis_.