to look forward and outward, and in the middle shows a large ovate
pneumatic foramen. Behind, the wedge is compressed so as to look
backward and downward.
The neural spine is massive and forms rather more than half the height
of the vertebra. It is flattened with a ridge rising near its base in
front and ascending in a concave curve obliquely backward and upward.
The anterior parts approximate a little in front, while the small parts
posterior to the ridge approximate a little behind. The sides of the
neural spine approximate superiorly, and appear to round into each
other.
There is a notch on each side in front at the base of the neural spine,
and another above the central articulation. The neural spines appear to
have been united by suture. It may be instructive to compare the neural
spine just described with the specimens =J=. _c_. 10.
Of the second type or genus No. 4 to 7 all show the anterior cup for
the last lumbar vertebra. No. 3, 5 and 6 all show two entire vertebræ
and part of a third preserved, but no specimen shows the posterior
termination of the sacrum. No. 7 has the articular face of the centrum
very broad, and greatly depressed. In No. 6 it is ovate and has the
neural arch preserved; above a semicircular neural canal it sends
out on each side a short horn-like zygapophysial process. No. 4 is
remarkable for the small size of the circular neural canal, the centrum
when entire measuring an inch from side to side, while the neural canal
only measures 5/16 of an inch. No. 5 is figured by Prof. Owen. No. 4-6
appear to have given off transverse processes from the sides of the
centra. No. 7 appears to widen into transverse processes at the point
of suture between the centra.
In No. 3 the base of the sacrum is flattened, and its sides pinched in,
and concave in outline from back to front. In this hollow are small
pneumatic foramina, and between the hollows the vertebræ widen in the
line of the suture so as to send out strong short transverse processes
or tubercles. Above the hollows are given out the strong horizontal
quadrate pyramidal transverse processes. All their sides are flattened
or a little concave, and the under side displays a large ovate
pneumatic foramen. Each of the four angles of the transverse process
gives off a ridge. The lower ones descend obliquely to the anterior
and posterior intersutural tubercles. The upper two ascend obliquely,
in front and behind, and form rounded ridges on the neural spine. The
neural spine is flattened, moderately compressed from side to side, and
cupped a little over each transverse process. In front the neural spine
is flattened transversely and perpendicular; the transverse processes
are also flattened and a little in advance of the neural spine.
The sacrum in its general aspect is Mammalian. In the Bird the
vertebræ are much more numerous and do not retain their individuality
so well. In Reptiles properly so called, the sacrum never includes more
than two or three vertebræ, and those commonly remain unanchylosed. But
in almost any placental Mammal in which several vertebræ are anchylosed
together, a sacrum similar to that of the Pterodactyle is met with. No
mammalian sacrum, however, is furnished with pneumatic foramina.
Caudal Vertebræ.
Pl. 10.
Case. Comp. Tablet. Specimen.
=J= _c_ 5 1-13
Thirteen specimens are mounted to exemplify the osteology of caudal
vertebræ. No. 7 has been figured by Prof. Owen in the memoir on
Pterodactylus simus, pl. 2 fig. 13-16. The centrum of the largest
specimens measures one inch and a quarter long, and the vertebra
is half an inch wide from side to side in the middle. The smallest
specimen No. 13 has the centrum 3/4 of an inch long. The vertebræ vary
in proportions, some being much more slender than others. They present
a close approximation in form to the first type of cervical vertebræ,
differing chiefly in being more elongated.
They are elongated bones constricted in the middle, so that the
outlines of the sides seen from above or below are gently concave;
the outline of the anterior end is sub-rhomboid, the outline of the
posterior end is sub-pentagonal, as would be a transverse section of
the vertebra. The long outlines of the base of the centrum and of the
top of the neural arch are sub-parallel.
The two sides of the upper surface of the neural arch are smooth,
flattened, a little concave from back to front; they are inclined to
each other pent-house wise at about a right angle, and are separated
throughout their length by a narrow slightly elevated neural spine.
Behind, the neural arch is truncated transversely so as to expose
the posterior neural surface of the centrum, which is convex from
side to side. The outermost lateral angles of the neural arch are the
posterior zygapophysial processes, short and strong above the centrum,
with a tubercle on the upper surface, and showing the sub-circular
zygapophysial facets behind; they look backward and downward, and
are separated by a groove from the region of the centrum. Under the
sharp ridge which connects these zygapophyses behind, the neural arch
is excavated, and the cup shows the termination of three canals. The
largest one is the upright oval of the neural canal in the middle,
on each of its sides separated by a narrow bony wall is another
perforation, very variable in size and shape, sometimes b& large as the
neural canal, but usually small and circular. The anterior end of the
neural arch is cut into, so that as seen from above, the straight sharp
anterior margins diverge mesially from each other at a right angle, and
so expose to view a small anterior part of the neural surface of the
centrum. These lines are prolonged forward and outward, to form the
upper margin of the anterior zygapophyses, which are compressed and
prolonged over and beyond the sides of the anterior articulation, from
which they are separated by a slight groove; the anterior and posterior
zygapophyses are connected by a rounded ridge. The anterior end of the
neural arch is excavated, but less so than the posterior end; in the
middle is the oval perforation of the neural canal, and at the sides
other perforations corresponding to those behind are placed a little
in advance of the neural canal. The anterior and posterior articular
surfaces differ in no respect from those of cervical vertebræ.
The inferior surface of the centrum is separated from the sides by two
ridges parallel to the lateral concave outlines of the neural arch;
they extend from sides of the front, more or less well marked, to the
tubercular processes at the base of the sides of the centrum behind.
The dice-box shaped area of the centrum so inscribed is usually concave
from front to back, and concave from side to side behind, and convex
from side to side in the middle; this convexity is only broken in front
by the development of the slight mesial hypapophysial ridge.
The sides are narrow, flattened, look downward and outward, are a
little concave from front to back, round into the centrum and into the
neural arch, and show at about the middle a small pneumatic foramen,
which is variable in size, but largest in No. 8, and sometimes a mere
puncture.
The caudal vertebræ differ in many ways from other animals. They
have neither transverse processes, neural spines, hypapophyses or
hæmapophyses. In the persistence of the neural arch down the tail they
resemble reptiles and birds rather than mammals, in which nothing but
the centrum persists to the end of the tail. The vertebræ are furnished
with vertebral arteries which run through the neural arch parallel to
the neural canal, in exactly the same position as do the vertebral
arteries in the neck-vertebræ of the Llama.
THE BONES OF THE HEAD.
Pl. 11, 12.
The skull of Dimorphodon differs in form and in many important details
of structure from that of Rhamphorhynchus; and both of these types of
skull are strikingly unlike that of the short-tailed animals named
Pterodactyle. Hence, as it will be shown that the Cretaceous fossils
of this class belong to very distinct new genera, there is no reason
for assigning to them by anticipation any class of cranial structures.
The cranium of this type of animal has never been critically described,
and for all that is yet known to the contrary Pterodactyles may differ
between themselves as much as birds or mammals. Their affinities have
been unknown. Therefore, before describing bones it may be desirable
to state the grounds on which the several specimens are referred to
the Ornithosauria. The fossils on which this section of the memoir is
founded are, the basi-occipital and basi-temporal bones, the anterior
portion of a cranium, the back parts of four crania, facial bones, and
the quadrate and quadrato-jugal.
The crania are all no larger than that of the Heron; though from
the Greensand are bones and jaws indicating Pterodactyles both
smaller and larger. The skulls are mostly remarkable for wanting
both basi-occipital and basi-temporal bones. And the specimen of
basi-temporal and basi-occipital corresponds posteriorly with the
Pterodactyle atlas, anteriorly with these crania; it is hence concluded
to have belonged to a similar animal. Being relatively twice as
large, it indicates that in these animals the basi-occipital condyle
was proportionally larger than in known birds; and that animals of
a cognate kind had skulls probably twice the size of these. The
anterior basal part of the hinder sphenoid terminates in a remarkable
triangular surface, with two perforations, which are separated by a
median ridge. Almost entirely corresponding with this is the basal
surface of the anterior part of a cranium, fractured in front of the
pituitary fossa. Therefore, and as it indicates a similar capacity of
brain, it is regarded as belonging to the same kind of animal as the
others ; but being five times the size, it must, if the proportions of
the Heron were preserved, have been part of a head a yard long.
Now, as there is no other animal with the same texture of bone, or
exhibiting with high organization the same diversity of size, these
cranial fragments are referred to the jaws and bones of Pterodactyle.
So marked are their structures that many quarry-men refer vertebrate
fossils to their several orders with almost as much accuracy as would a
practised anatomist.
Basi-occipital and Basi-temporal.
Pl. 11.
Basi-occipital, Owen, _Sup. Cret. Rep._ p. 6, T. 1, figs. 11, 12, 13.
Case. Comp. Tablet.
=J= _c_ 7
This bone was not found associated with any set of fossils that
would induce us to refer it to one species more than to another. Its
Ornithosaurian character was probable; and Prof. Owen described it in
his last memoir on the Greensand Pterodactyles.
But though indubitably basi-occipital, it is so anomalous in some
respects that the Professor regarded the under as the upper surface;
since then the investing phosphate of lime has been removed, and the
bone is now described in what appears to be its natural position.
Viewed from above the fossil divides into two parts; the occipital
condyle, and an anterior, wide, transversely oblong extension
terminating at each side in a strong short horn. The posterior half
of the condyle shows large cancelli as though so much of it had been
covered by the articular cartilage. The sides of the condyle converge,
so that posteriorly it is only two-thirds of the width it has at the
foramen magnum, which would appear to indicate a comparatively slight
lateral motion of the head. The condyle is hemispherical posteriorly
and superiorly; there is a depression between it and the great foramen
of the skull; inferiorly it is flat.
It is 7/16 of an inch long; posteriorly 9/16 wide, nearly 6/16 of an
inch high anteriorly. It terminates in front superiorly in an elevated
transverse ridge.
On removing the matrix, the anterior surface of this occipital bone
was found to be concave; yet as nothing but cancellous structure is
seen it may be but imperfectly ossified or more probably, imperfectly
preserved. And the bottom of this cup expands forward in a thin sheet
of bone a quarter of an inch long and half an inch wide, which on the
under side is continuous with the base of the condyle.
On each side of this floor and partly extending in front of it, and
below it, is an irregular piece of bone, half an inch long, resembling
anterior zygapophyses of cervical vertebræ.
Though in most vertebrates the basi-occipital enters into the basal
floor of the skull, the median bones are either so placed that they
rest one upon another from before backwards or abut against one another
nearly perpendicular, so that the basi-sphenoid comes commonly to
underlap and partly hide the basi-occipital. Nowhere among Amphibia or
Reptilia do I know of the reverse position occurring. In some fishes
there is an approach to it. Thus a slight anterior bony expansion of
the basi-occipital in the Cod fits partly into a horizontal slit in
the basi-sphenoid[A]. In the Carp the basi-occipital has a spathulate
basal expansion like that of Pterodactyle, but it is underlapped by the
basi-sphenoid[S]. In some mammals the under side of the basi-occipital
extends further forward than does the neural side, as for example
in the Sheep and Goat; while in a few others, as in the Walrus, the
reverse positions obtain.
[Footnote S: Parasphenoid of Prof. Huxley.]
But it is among Birds that the structure described in Pterodactyle
is evident and characteristic. For although the bony plate under the
sphenoid,--Mr Parker's basi-temporals,--is mostly anchylosed to the
bones about it, and less with the occipital than with others, its
position and relations are quite the same as those of the expanded flap
of this Pterodactyle basi-occipital. Therefore it is identified with
the basi-temporal bones.
Back of the Cranium.
Pl. 11.
Case. Comp. Tablet. Specimen.
=J= _c_ 8 1
This fossil is an inch high, rather wider, and half an inch long. It
well shows the bones at the back of the skull, the basi-cranial bones,
and the bones posterior to the frontals, which roof in the Cranium.
There are in it striking resemblances to the back of the skull of some
Natatores, as the Grannet and Cormorant, and of some Grallatores as the
Heron, and Gallinaceous birds as the Cock.
_The base of the skull._ The bones here indicated are the
basi-occipital, basi-temporal, and basi-sphenoid. The former two
have come away as from an articular joint, and are wanting. The
basi-occipital does not enter into the floor of the cranial cavity, and
only rims the foramen magnum. But its basi-temporal expansion rests
beneath the posterior part of the basi-sphenoid forming the base of the
skull; its long convex anterior end fits into the concave groove at the
back of the anterior part of the sphenoid. The squamous basi-temporal
bone appears in this species to have been as long as the foramen magnum
is wide, and to have been relatively thicker than in the other form
already described.
The _basi-sphenoid_ is a thin expanded bone forming the floor for the
cerebellum, and terminating anteriorly in a triangular mass, while the
slightly convex part behind, covered with the basi-temporals, is nearly
square. It enters into the foramen magnum, forming its lower part;
and is confluent with the ex-occipitals behind, with the periotic,
alisphenoid and perhaps with the squamosal at the side; and as in birds
all these sutures are obliterated. This is probably the only instance
in the Animal Kingdom in which the basi-sphenoid takes so important
and singular a share in the functions of the basi-occipital bone. The
anterior part of the basi-sphenoid projects below the posterior part,
is nearly flat on the basal surface, and forms an equilateral triangle
with the apex in front and base behind. In the middle of the triangular
bone is a slight longitudinal ridge, and behind the middle of each
outer side a rather large foramen which appears to be the inferior
opening for the carotid artery. The triangular part is hollow and as
long as the quadrate portion. The lateral parts of this anterior bone
are nearly flat. They converge upwards and are rounded in front to
form the boundary of the pituitary fossa, and do not appear to have
terminated in a spine. Above are the alisphenoids.
_The upper part of the skull_ is divided into two segments by a strong
straight transverse ridge, which leaves the occipital bones behind, and
the parietal &c. in front.
The occipital bones anchylosed together are about two-thirds the width
of the foramen magnum, and of the parietal bones, with which latter the
supra-occipital makes an angle of 45°. The surface is irregular, and
especially is marked by a deep concavity just above each ex-occipital.
The supra-occipital projects slightly over the plane of the foramen
magnum, to which the strong ridge bounding the segment in front is
parallel. The great foramen is nearly round, being slightly compressed
at the upper part of the sides: it measures 3/8 of an inch high and is
nearly as wide.
The _occipital bones_ make with those at the base of the skull an
angle of about 145° or 150°. In outline they are a transverse diamond
shape. The mastoid portion is not to be distinguished from the other
bones, but appear to terminate the sides of the strong occipital
crest, which by posterior compression of the squamosals and parietals,
becomes very strong, and makes the backward boundary of the temporal
foss. This crest is in the same plane with the anterior border of the
basi-temporals.
The _parietals_ meet above in a slight ridge. They are two rectangular
bones twice as wide as long, forming a semicircular roof for the brain,
which looks outward and a little backward. Anteriorly these bones
unite with the frontals in a slightly flexuous transverse line; and
inferiorly they are connected with the periotic, the squamosal, and
perhaps with the anterior point of the alisphenoid: they do not descend
to the plane of the articulations of the free quadrate bones. The
surface is smooth, and on the upper part flat, but concave below from
side to side.
Below these parietals are the _squamosals_ and _alisphenoids_, but the
suture between them is not seen. They are in form a trapezium where
the short side is anterior, and the lower third is folded inward so as
to be confluent with the anterior part of the sphenoid. The fold forms
a ridge, which I suppose may run obliquely over the alisphenoid. The
unfolded squamosal part is a flat and smooth oblong, with parallel
sides, the bones are in parallel planes and nearly perpendicular to the
base of the skull. Where the alisphenoid joins the sphenoid, there is
a considerable concavity, above which is a small circular impression.
These strips approximate inferiorly, so that the width of the skull
there is rather more than half what it is at their outer margins. They
shut off the pituitary body in front of them, and appear to form part
of the wall for the orbit of the eye.--The slightly convex, lateral,
squamosal parts above the fold continue the circular transverse outline
of which the parietals are the upper half. They extend anterior to the
parietals, and on the inside give attachment to the frontals. Like the
parietals, they make a sharp bend outward at their hinder border, and
form the lateral terminations of the occipital ridge, which is the
widest part of this fossil.
The only portion of the specimen now to be described is the large
region at each side looking downward, which extends from the occipital
ridge to the sphenoid. It is an irregular pentangular hollow with many
cavities, the hinder of which are for the ear. Two cavities above
these, under the widest part of the skull, appear to be a double
articulation for the quadrate bone. The outer transverse one with
the squamosal is separated by a deep groove from the inner and more
vertical one, which may therefore be regarded as with the petrosal
bone. These excavations form the posterior half of the pentagon. The
anterior half is a smooth rhombus not separable from the basi-sphenoid.
Such is the external appearance of the occipital and parietal segments
of the skull of a Cambridge Pterodactyle. Each segment forms a large
ring of thin bone, inclosing part of a brain-cavity as large as that
of a bird and shaped like that of a bird; and which moreover is made
up of the same bones as the cranium of a bird; and these are in almost
exactly the same proportions as those of the Common Cock.
My own investigations do not substantiate Wagner's discovery, that the
back part of the skull resembles that of the Monitor. Iguana would
have offered a slightly nearer comparison, but they both differ from
Cambridge specimens of Pterodactyles in characters like these.
In the lizard,
The cranial bones do not enclose the brain.
There is no division of the back of the skull into an occipital
segment and a parietal segment by a girdling crest.
The squamosal bone does not enter into the cranial wall.
The quadrate bone does not articulate with the wall of the brain-case.
While the peculiar backward development of wings of the parietal in a
diverging V form, give the Lizard skull an aspect of its own.
So that it must be asserted that the differences of these Pterodactyles
from Lizards are so wide as to preclude comparison.
With the Crocodile, in which the cranial bones are massive, and the
quadrate bone firmly packed in the skull, comparison would be no less
difficult.
The Delphinidæ, in both the form of the jaws and of the back of the
head, give some support to Wagler's fancy, in putting the Pterodactyle
into his curious creation, the Gryphi[T]. But in the porpoises the
parietal bones form as narrow a band as they do in the Duck; and are
quite unlike the bones here described. In the Dolphin the two condyles
almost unite into one semicircular condyle (in young specimens), owing
to the enormous development of the ex-occipitals, which almost if
not entirely exclude the basi-occipital from the foramen magnum. The
dolphin moreover has no quadrate bone. But notwithstanding the absence
of a division into occipital and parietal segments, the form and
arrangement of the bones in the skull of the porpoises approximate more
to the Cambridge Pterodactyles than is the case with Lizards.
[Footnote T: The Gryphi are a class of animals intermediate between
Birds and Mammals according to Wagler, and including Pterodactyles,
Ichthyosaurus, Plesiosaurs, Ornithorhynchus, and Myrmecophaga.]
But with Birds the correspondence is so close that it would be
difficult to discover differences. That one of the condition of the
occipital bone seems to be the most important; another is, that from
the relatively smaller size of the cerebellum the parietal bones appear
to cover a larger part of the cerebrum; and a third is the strong
triangular condition of the sphenoid in front of the sella tursica.
With these exceptions there is nothing to distinguish the fossil
described from the cranium of a bird.
Back of another Cranium.
Pl. 11. fig. 1, 2.
Case. Comp. Tablet. Specimen.
=J= _c_ 8 2
Another cranium has occurred which must be referred to a different
genus. Its preservation is less perfect, but it similarly exhibits the
occipital and parietal segments of the skull. All the bones are blended
together without a trace of a suture.
The _occipital region_ is flat. Its outline is not defined owing to
the extent to which the sharp crest, in which it terminated outwardly,
has been broken away. The occipital condyle is broken off. The foramen
magnum is of an ovate form--flattened at the base. The ex-occipitals at
its sides are impressed as though from contact with the neurapophyses
of the atlas. Mesially, over the foramen magnum is a vertical elevated
crest (now rubbed away), which may have given attachment to a bone
like that post-superoccipital crest described by Quenstedt in the
_Pterodactylus suevicus_. The occipital region makes a great angle with
the flat basi-temporal region, as in birds.