shaft-like, as in the Chameleon. The articulation of the quadrate with
the lower jaw is placed further forward than in birds and reptiles. The
lower jaw, but for the teeth, has great similarity with that of a bird.
Among reptiles its nearest resemblance is with Chameleons and Turtles.
The hyoid is more bird-like than reptile-like.
_Ribs and vertebræ._
It is uncertain whether the Pterodactyle had lumbar vertebræ. If they
are wanting, therein the animals resemble birds, of which we are
reminded in the short and stiff back and moveable neck. Pterodactyles
possess a smaller number of neck-vertebræ and a larger number of
back-vertebræ than birds. The long neck-vertebræ are paralleled by
those of water-birds, by the Giraffe, the Camel, Protosaurus and
Tanystrophæus. There are 7 cervical vertebræ, the 1st very short, 2nd
not longer, but rather shorter than those which follow. There are in
Pterodactyles from 12 to 16 dorsal vertebræ, while birds have never
more than 11. It is not certain whether all Pterodactyles have an os
sacrum; most have it, and therein resemble Mammals, Birds, and some
fossil Saurians. In Pterodactylus dubius and P. grandipelvis and P.
Kochi there are 5 or 6 vertebræ in the sacrum. In birds the sacral
vertebræ vary from 5 to 22; in bats the number is from 5 to 6.
The short tails of Pterodactyles are more like those of mammals than
birds; they include from 10 to 15 tail-vertebræ. In birds there are
from 6 to 10 tail-vertebræ. Rhamphorhynchus has 38-40 tail-vertebræ,
secured between thread-bones like those in the tail of rats.
The dorsal ribs are reptile-like. In herbivorous mammals and birds
they are broader. A few species have the first pair of ribs large. The
abdominal ribs belong neither to birds nor mammals, but are reptilian.
In Rhamphorhynchus Gemmingi there are 6 pairs of sternal ribs.
_The sternum_
is bird-like, somewhat resembling lizards. It consists of a simple
flat bone, but without the keel of a bird's sternum. It is relatively
smaller than in birds, is broader than long, and therefore comparable
with Struthious birds. They were not able flyers, since the part to
which the muscles for flight should be affixed is wanting. And for
the same reason they could not have been wandering animals. But Moles
possess a keel on the breast-bone, which therefore is no evidence
of flight. And in swimming-birds which do not fly the keel is much
developed; and in swimming-birds the sternum is also long, so that
neither length nor keel prove flight. So far as the evidence from the
sternum goes, they were neither water-birds, nor diggers, but denizens
of the air. In Rhamphorhynchus Gemmingi, besides the usual breast-bone,
there is a plate with breast-ribs uniting the sternum with the dorsal
ribs; they are cartilaginous, or horny, as in birds.
_The scapula and coracoid_
present the closest resemblance with those of a bird, and only deviate
in the coracoid not being inserted in the breast-bone in the manner
of birds[M]. It at first seemed that Rhamphorhynchus differed from
Pterodactyle in having the scapula and coracoid anchylosed. In R.
Gemmingi the bones are either separated or only slightly united.
[Footnote M: See however Pl. 1 and 2 of this memoir.]
Oken and Goldfuss thought that the scapula consists of an upper and
under part, as in lizards. Von Meyer sees nothing of the kind.
_The humerus_
presents no striking similarity with birds, and differs from bats.
_The carpus_
is more reptile-like. It consists of two rows of small bones. In birds
there is one row made up of two bones.
_The pteroid bone._
Von Meyer regards it as having supported the wing-membrane in flight.
There has been a good deal of difference of opinion about it, some
thinking it, with Quenstedt, an ossified tendon; others, like Wagner
and Burmeister, regarding it as an essential part of the Pterodactyle
skeleton. Von Meyer regards its extent as indicating the extent of the
wing-membrane. See p. 42.
_Metacarpus._
In length the metacarpus resembles that of the Ruminants, in which
however it consists of but one bone; while in Pterodactyles there is
a separate bone for each of the four fingers; they are closely united
together without being blended. In some Pterodactyles the metacarpals
of the short fingers are as fine as hairs, so that it is impossible
that they should have articular facets on the carpus. In Ornithopterus
the metacarpus has some resemblance with that of the bird, but the
articulation with the phalanges of the finger for flight is stiff. In
Pterodactylus and Rhamphorhynchus there is a free articulation.
Burmeister remarks that the chief articulation of the wing in bats is
with the carpus, while in Pterodactyle the articulation is with the end
of the metacarpus.
_The hand._
Von Meyer finds four fingers. It was formerly supposed that the order
of the phalanges was 2, 3, 4, 4, but in the fly-finger this is not the
case, Ornithopterus having but two. The number of joints in the other
fingers is quite as irregular.
In Pt. longicollum the thumb consists of but one joint.
_The Ilium_
is more mammalian and avian than reptilian.
_Pubis._
The pubis appears to have been excluded from the glenoid cavity, as
in Crocodiles. It is more mammal-like than bird-like, and is to be
compared with the marsupial bones.
_The femur._
In certain Pterodactyles the proximal condyle of the femur resembles
birds; but in other Pterodactyles the bone is more mammal-like in its
straightness, and development of the upper condyle, and in the presence
of a trochanter.
_The tibia and fibula_
may be compared, from their great length, with birds and flying
vertebrate animals.
The fibula is style-shaped, like that of a bird, the lower part being
wanting; while in bats the upper part is wanting.
_The tarsus,_
of two rows, is best compared with that of reptiles. The number of
constituent bones has not been definitely determined.
_The metatarsus_
shows a certain return from the bird type to that of reptiles.
_Foot._
Von Meyer never finds more than four toes, and sometimes a stump of a
fifth. As a whole, the foot is Saurian-like. It differs from lizards in
the number of toes, and approximates to Crocodiles. In Pterodactylus
longirostris the formula of the toes is 2, 3, 4, 5, with a stump of two
joints;--like lizards, if we abstract the outer toe; and like birds
with four toes; but they are liable to variations.
In Pterodactylus scolopaciceps and P. Kochi the formula is 2, 3, 3,
4 joints. In Winkler's specimen of P. Kochi there is also a stump of
three joints.
In Pterodactylus micronyx the formula is 2, 3, 3, 3, and a stump of two
joints. In P. longicollum the number appears to be different from all
the foregoing.
The stump was attached to the side of the outer toe. Wagner, in P.
Kochi, supposed it to be on the inner side, and so gave a reverse
arrangement to the toes. The stump may be compared with that of some
Chelonians, in which it is not furnished with a claw.
There is a difference from birds in the claws being much less
developed. It has a true reptile foot. In bats the toes are of equal
length. Von Meyer thinks the hind-legs did not enable it to walk on the
land.
In some Pterodactyles the flying-membrane is faintly seen. The presence
of feathers might be inferred from there being but one finger for
flighty as in birds; but the function of feathers is subserved by the
long and stiff finger. If it had been covered with scales, as was
supposed by Cuvier, some traces of them would be found. The skin was
probably naked, and had no connection with the hind-legs as it has in
bats; in this respect resembling birds.
The condition of the several parts of the skeleton completely proves
that the Pterodactyle was a reptile. Its head, neck, shoulder, and
back, resemble a bird; while there are, on the other hand, some
striking resemblances with the reptile in the pelvis, tail, and
articular parts of the limbs. Sometimes the characters of the two
classes run side by side, as in the skull, the fore-limbs, and
especially in the hind-limbs, where the shin of a Bird is connected
with the foot of a Saurian. The parts in which it corresponds with
birds show that Pterodactyles also were flying animals. That we should
be entitled to conclude, from the hollow state of the bones, that they
belonged to flying animals, is sufficiently proved by Blumenbach,
Buckland, Mantell, Owen having mistaken them for bones of birds.
The most absolute proof that it was a flying animal is the pneumatic
character of its bones. This condition was discerned by me in some
Pterodactyle bones from the Lias of Franken (_Jahrb. für Mineral_,
1837, p. 316), and was afterwards established by Owen in the
Pterodactyles from the Chalk of England. This structure was previously
only known in birds. And the supposition readily follows that in the
respiratory process there was some similarity between the Pterodactyle
and the Birds. They have the proportions of upper-arm and fore-arm
which characterize birds of great flight, the humerus short and the
fore-arm long; hence it may be presumed that Pterodactyles could fly
well. From the absence and presence of the bony sclerotic ring in the
eye, it may be supposed that the Pterodactyles were active in the
day-time, while Rhamphorhynchus was nocturnal.
After this statement von Meyer gives a discursive summary, in which his
views of the classification of reptiles in general and of Pterodactyles
in particular are epitomized. And then goes on to combat the views of
people who have departed from his classification and attempted to set
up classifications of their own; and cites a number of authors who,
labouring at the vertebrata, have endeavoured to find a resting-place
in their systems for the Pterodactyle. But the chief thing we learn of
von Meyer's own views is, that in 1830 he published a classification of
extinct Saurians, dividing them into those with limbs like the larger
and heavier land-mammals, those with fin-like limbs, and those with a
flying-finger. Which divisions have been widely adopted, though authors
have sometimes given them other names than those by which they were
first made known.
Von Meyer has freely stated the facts about the Pterodactyle, and draws
the conclusion that the animal was a reptile; but how such a conclusion
was obtained from such facts is a matter on which his pages are silent.
One seems to hear the chirrup of the bird in almost every paragraph.
The head is in the main a bird's head; the pectoral girdle and the
sternal ribs are those of a bird; and very few are the structures in
which some reminder of the bird is not present; and in their bones he
discovered the pneumatic characteristic and inferred, for the animals
bird-like lungs. How, then, comes it that the Pterodactyle is a
reptile? We can only suppose the answer to be, Because if the head and
pectoral girdle and other bones had been reptilian it would have been a
bird.
* * * * *
In the views here epitomized it is difficult always to make out the
logical foundations of the conclusions arrived at. Sometimes they have
no foundations, and sometimes they represent the different aspects
in which a truth presents itself to minds differently constituted
or differently conversant with the structures of living animals. In
now stating my own views I shall avail myself of the example of some
previous writers, and attempt to investigate the Pterodactyle as though
they had not written. And then, having placed before him all the
theories that are known, the reader will be able to choose the theory
that pleases him best, if indeed he needs one.
Much of the discrepancy of opinion that exists is probably due to the
use of the inductive method of thought for the discovery of fundamental
principles in classification. In palæontology, where the types are
more generalized than are living forms, it must always be difficult to
reason from the known to the unknown. The known is always more or less
incomparable with the unknown; and there can be no reason for inferring
that the specialities of structure which now accompany specialities
in organization would justify us in inferring for the animal, in which
the structures formerly were united, the combined organizations of
the living animals in which they are now found. On any hypothesis
of evolution it would be allowed that the special modifications of
a group were attained subsequently to the common plan of the larger
group to which it belongs, and are entirely to be attributed to the
function which the necessities or organization of the animal caused
its structures to subserve. Inductive thought may sometimes discover
function from structure, but never makes more than an approximate
guess when it endeavours to determine fundamental organization from
osseous structures which are not fundamental. And before a naturalist
can say, since an animal has for instance a tail like a mammal that in
so far it must be affiliated to the mammalia, he must have determined
why the mammalian tail has its peculiar characters, and whether it is
compatible with any other common plan of organization. And perhaps it
might with equal reason be considered reptilian.
Therefore I prefer at firsts instead of reasoning from the details
of structure, to adopt the _à priori_ method, and ask, not what the
Pterodactyle is like in its several bones, but what common plan it had
whereon its hard structures were necessarily moulded. For I imagine, if
it can be determined what the nervous and respiratory and circulatory
structures of the Pterodactyle were, it becomes a secondary matter to
know whether the phalanges are like a lizard's, or the pelvis like that
of a mammal. If the animal is asserted to be a mammal, a reptile, or a
bird, we ought to be able to adduce evidence that it had the soft parts
which are deemed distinctive of the selected class. This no one has
done or attempted to do.
Hereafter it will be necessary to describe the Pterodactyle's brain.
There is no organ more distinctive between hot-blooded animals on the
one hand, and cold-blooded animals on the other, than the brain. In
the cold-blooded groups, or those in which respiration is feeble and
circulation imperfect, that is to say, in existing fishes, amphibians,
and reptiles, the parts of the brain are arranged one behind another,
so that when looked upon from above, a portion called the optic lobes
intervenes between the anterior masses called the cerebrum and the
posterior mass called the cerebellum. In the hot-blooded groups, or
those with an enormous extent of lung-surface for oxidation of the
blood and a four-celled heart for its rapid circulation, that is to
say, in birds and mammals, the front part of the brain called the
cerebrum is immensely developed in proportion to the other parts,
and abuts against the cerebellum and more or less completely covers
the optic lobes, which in birds are squeezed out to the sides. The
Pterodactyle brain is of this latter kind. And it being taken as a
postulate that this kind of brain is the product of the organization
which produces hot blood, it follows that the Pterodactyle was a
hot-blooded animal.
Again, the Pterodactyle has perforations for pneumatic cells in many of
the bones.
There is no structure in the animal kingdom more distinctive of a
Class of animals than air-cells perforating the limb-bones. They are
connected with a peculiar kind of lung and heart--those of the bird;
for in this Class the bronchial tubes open on the outer surface of
the lungs into air-cells, which are prolonged through the body into
the bones. They follow the blood-vessels, and are most developed in
the part of the body most used. In some lizards, as the Chameleon,
the sack-like lung at its distal termination is as simple as the
air-cells of a bird; but those air-cells are not comparable with the
bird's air-cells, since they are not prolongations of the bronchial
tubes through the walls of the lungs. And it cannot be inferred that
a reptile with wings would develop air-cells like those of a bird:
in the first place, because those mammals which have wings do not
develop air-cells; and, in the second place, because there is nothing
in existing nature to lead any one to think that reptiles might have
wings. The mammalian lung is better comparable to that of a bird than
is the Chameleon lung, and therefore the air-cell structure might
with better reason have been anticipated to occur in the Chiroptera
than in a Lizard-ally, if it were dependent on the development of
wings. Moreover, among Struthious birds the legs have more of the
air-cell prolongations than the wings. Therefore, being a peculiar
Avian structure which only exists in association with the Avian heart
and lung, it follows that because the Pterodactyle had the pneumatic
foramina it also had the structures of which they are the evidence,
viz. lung and heart formed on the bird plan.
Thus Pterodactyles have a nervous system of the bird type. That kind of
brain only exists in association with a four-celled heart and hot blood.
They have a respiratory organization which is only met with among birds.
With that respiratory apparatus is always associated a four-celled
heart and hot blood, which it would necessarily produce.
And with that respiratory organization is always associated a brain of
the type that the Pterodactyle is found to possess.
_Therefore it is firmly indicated that the general plan of the most
vital and important of the soft structures was similar to that of
living birds._
This proposition will be incidentally proved in the following memoir,
in which it will be seen that with such a common plan, is associated a
diversity of details sufficient to demonstrate that these animals are
not birds, but constitute a new group of vertebrata of equal value with
the birds--the sub-class, Ornithosauria.
OSTEOLOGICAL COLLECTION
ILLUSTRATIVE OF THE MODIFICATIONS OF THE
ORNITHOSAURIA (OR PTERODACTYLES) IN THE
CAMBRIDGE UPPER GREENSAND.
Pectoral Girdle.
STERNUM.
Pl. 1, fig. 1.
Case. Comp. Tablet.
=J= _a_ 1
The Sternum is the key to the bony apparatus supporting the anterior
limbs. In the Pterodactyles from the Cambridge Greensand it has been
well figured and described by Professor Owen, who enunciated its
resemblance to the sternum of birds. The sternum in Pterodactyles from
the Lithographic Slate, shows its proportional size to the body. The
examples found in the Cambridge Greensand have as yet shown no evidence
of a composite character like that attributed to Rhamphorhynchus
Gemmingi.
The sternum consists of an expanded symmetrical shield having its
lateral halves, which are inclined to each other at a large angle
(about 150°), contracted superiorly, behind and immediately below the
synovial cavities for the coracoids. The vertical angular ridge in
which the lateral portions of the sternum unite becomes elevated as it
is followed anteriorly, into a strong keel. This keel or interpectoral
process is highest in front of the articulations for the coracoids; but
the degree of elevation varies with the species. It is prolonged upward
and in front of the coracoids for some distance, becoming very massive,
and the prolonged mass which is flattened from side to side, reaches
laterally to the outer margins of the coracoid articulations, and on
the visceral side a little between and over them. The anterior crest of
the keel shows the attachment of powerful muscles.
Professor Owen has observed that only in birds are distinct synovial
cavities provided for the coracoids, and that no reptile has a
sternum showing characters like those seen in the Pterodactyle. These
coracoid cavities are placed as in birds, close together, behind the
_manubrium_, which forms the hindermost part of the keel. They are
convex transversely, concave from front to back as in birds, and
look upward at an angle of 35°, their main direction being outward
and a little backward. Professor Owen recognises the function of the
shield-shaped sternum in relation to the mechanism of respiration on
the one hand, and on the other hand, for the attachment of pectoral
muscles of great bulk and strength.
As is well known, the muscles of the breast in most birds consist
chiefly of the 1st, 2nd, and 3rd pectoral muscles, and the
coraco-brachialis.
The peculiar form of the bird's sternum appears to be due to the
vertical development of the second pectoral muscle, since when the 1st
and 3rd muscles are dissected off, the appearance presented nearly
resembles that of the sternum in Pterodactyles. There can however be
no doubt but that the third pectoral muscle, which in most birds is
but feebly developed, attained a far greater bulk in the Pterodactyle,
because there is evidence of its powerful insertion in the distal
anterior face of the coracoid, as well as of the great lateral
extension of the sternal shield to which such a muscle must--by the
analogy of birds--have been attached. The peculiar lateral emargination
of the sternum appears to be due to the anterior sternal termination of
this muscle, caused by the outward direction of the coracoid bone.
Since the coracoids were developed outward and backward so much more
than in birds, it would happen, from the apparent different direction
of the second pectoral muscle, that the first pectoral muscle which in
birds skirts the furculum, must have passed over the coracoid, probably
pulling on its inside in opposition to the third pectoral. Either a
subdivision of this muscle or a distinct muscle in the same place, in
function corresponding to the subclavius muscle, appears to have been
powerfully attached from the anterior prolongation of the keel of the
sternum to the front face of the coracoid. It is improbable that the
second pectoral muscle was undeveloped, but merely directed differently
to what it is in birds, since, as will be seen, there is a process at
the proximal end of the coracoid homologous with that which forms the
pulley round which this muscle in birds works.
Professor Owen concludes his remarks by observing that the Pterosaurian
breast-bone is in the main formed on the ornithic type. The muscles
also appear to be similar to those of birds.
All the specimens are much mutilated, but all show the distinctive
post-coracoid lateral emarginations, but as these are not seen in
German Pterodactyles they are to be regarded as characters of a
peculiar sub-order and not as characteristics of the sub-class.
The example figured in this memoir and by Professor Owen is 2-5/8
inches in antero-posterior measurement, probably about one third its
entire length.
A small example in the collection of Mr Reed of York extends 1-1/4
inch in the same measurement, and by the analogy of _P. suevicus_ was
more than twice that length when perfect. It is remarkable in that the
coracoid facets look much less outward and much more backward than in
the larger species.