Part 9

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.

The _parietal region_ is convex from below upward, the lateral parts converging towards the crown, which however presents a broken and worn surface. From side to side the squamosal and parietal bones are concave, owing to the extended occipital crest behind, and the rapid widening of the skull in front caused by the large size of the brain.

In _front_ is seen a section of the brain-cavity. It is very like in form to the two halves of a pear put together side by side with the stalk downward. I have removed some of the phosphate of lime from the brain-cavity, and although it has not been excavated to the cerebellum, the great depth of the brain is well seen, and the convex character of the cerebral lobes, between which a crest of bone descends mesially as in the ethmo-sphenoid mass next described. At each of the lower outer angles of the brain, extending into the cancellous brain-walls to the outermost film, is an ovoid convexity, covered with a thin film of bone. They entirely correspond with the optic lobes, being in exactly the same position as in birds, only relatively rather small. Underneath the optic lobe on the outside is a small concavity, apparently the articulation for the quadrate bone. The basi-sphenoid mass below the brain is of considerable height, the upper half flat and smooth, the lower half fractured and cancellous.

In the main this skull is like the other one, differing chiefly in the depth of the sphenoid, in the mesial ridge between the cerebral lobes, in showing the optic lobes, and in having anchylosed basi-temporal bones. There would hence appear to have been considerable variations in the skulls of Pterodactyles even in the Cambridge Greensand.

Orbito-ethmo-sphenoid bone.

Pl. 11.

Case. Comp. Tablet. =J= _c_ 9

The symmetrical bone which I have so named is a wedge-like mass tapering in front, keeled above; flattened below, and cupped behind on each side. It belonged to a very much larger animal than the last fossil, and probably to a very different genus.

The _inferior surface_ is triangular, an inch and an eighth wide behind, at the base, and an inch and a quarter long; but it is broken at both ends. In its longitudinal median line is a strong keel stopping short in front, dying away behind, and forming with the compressed margins a considerable hollow on each side, at the back part of which is a large oval foramen. This surface, though five times the size, corresponds in form, ridges, and foramina with the anterior part of the sphenoid described in the article on the back of the cranium.

The _posterior surface_ is at right angles to the inferior one, but its lower third shows only fractured phosphate of lime filling perhaps the anterior part of the pituitary fossa. Its upper part also is broken. But on each side is a large concavity measuring in the fractured fossil an inch and a quarter high, three quarters of an inch wide, and half an inch deep from the unbroken median ridge where the cups become confluent at their base. The whole specimen is two and a quarter inches high. From the determination of the under side it follows that these smooth hollows, over each of which an impressed mesial line descends obliquely outward, are a part of the anterior boundary of the brain.

From the middle of the outer convex border of the oval remains of these cups for the cerebral hemispheres, a strong blunt ridge descends obliquely down the sides of the bone to terminate the compressed anterior end of the bone just in front of the hypapophysial ridge of the sphenoid. Above this ridge the bone is much compressed anteriorly, forming a strong straight mesial keel above, which rapidly approximates to the base; the height of the bone in front being one inch and a half, which is also its extreme length.

The region below the oblique ridge is a concavity, but it is a little compressed from side to side behind, and has the same anterior compression, so that the elongated oval of the fracture at the anterior end of the bone is only three-eighths of an inch wide.

The superior ridge will probably have supported the frontals, and the anterior end would terminate in the orbito-sphenoid.

The lateral ridges appear to correspond with what Prof. Huxley has described in the Ostrich as the ridge indicative of a supra-presphenoid ossification pointed out by Kölliker. The groove which is here noticed on the cerebral surface may indicate the same division. If so, the upper and anterior part of the mass would be the ethmoid.

This mass offers a considerable resemblance to the frontal portion of the skull of a dolphin (_e. g._ Delphinus delphis) from which the maxillary, premaxillary, palatine and nasal bones have been removed. But in the Porpoise the mesial ridge dividing the cerebral hemispheres is not prolonged so far forward as in the Pterodactyle; the cranial bones are often as smooth on the inside. Notwithstanding Wagner's assurance that the Pterodactyle skull is very like a Monitor's, he would have looked in vain for an ossification in Monitor, Iguana, or other Lizards, comparable with this mass. And although the brain is closed in front by bones in Serpents, it is by the frontal bones, which form a covering for nearly the whole of the conical cerebrum. Nor in the Crocodile is there any ossified mass in front of the brain, although the brain approximates nearer to Birds than is the case with other living Reptiles. Among Birds such a structure as that of the Pterodactyle is characteristic, but no bird has it so massive and mammal-like, though an approximation is made in some thick-skulled birds like _Ciconia marabou_. And in birds it usually is prolonged much further forward than appears to have been the case with Pterodactyle, where from the rapid tapering of the mass in front it appears to have ended in a vertical ridge like that in Parrots and Birds with a moveable beak. In Birds there is usually a median ridge dividing the cerebral hemispheres, but there is also often a small olfactory lobe prolonged in front of the cerebrum, to which nothing analogous is indicated in these fossils.

NATURAL MOULD OF THE BRAIN CAVITY OF A CAMBRIDGE ORNITHOSAURIAN[U]. (Cast.)

Pl. 11.

[Footnote U: For the opportunity of making this description, I am indebted to the kindness of John Francis Walker, Esq., M.A., F.G.S., F.C.S., &c., who some time since forwarded to me the whole of his rarer Ornithosaurian remains for description in the Geological Magazine,]

The original specimen is in the collection of J. F. Walker, Esq., of Sidney Sussex College. When found it only displayed the front of the cerebral hemispheres, and Mr. Walker generously gave me permission to remove the investing cancellous bone and phosphate of lime, and thus exhibit the form of the cerebrum and its relations to the cerebellum. The lower part of the brain is not preserved. But adherent to the sides of the fossil are still left parts of the temporal bones, and part of the bone at the back of the orbit which closes in the brain. The form of the cerebellum is not quite perfect behind, but it must have been unusually small.

The cerebral lobes taken together are much wider from side to side than from back to front, and have a transverse elliptical outline, except for the mesial notch behind for the cerebellum. The lobes are a little flattened above, and divided from each other by a deep mesial groove, which makes each lobe convex from side to side. They are well rounded at the front and at the sides, and are a little compressed towards each other below in the region of the orbits. Behind they become covered superiorly as in birds with a greatly thickened part of the squamosal and parietal bones. The surface of the cerebrum is smooth. There is no indication of a pineal gland. The cerebellum is small, like a pea between two filberts. It is sub-hemisphercal, is placed close against the cerebrum, and appears to give off narrow lateral parts, like those seen in many birds, only that they abut against the back of the cerebral lobes as in the Hare and some Mammals. In no reptile is there a brain in which the cerebrum embraces the front of the cerebellum, or in which it attains to such an enormous size. Fœtal Mammals (_e. g._ the horse and the sheep), even when they have attained to a considerable bulk, and many adult mammals, still have the optic lobes dividing the cerebrum from the cerebellum as in Reptiles.

The only Mammal which shows any near approximation to this brain is the _Ornithorhynchus_, in which the cerebellum is very small, but the cerebrum is not so well rounded in front. The form approximates to the brain in Man. But with Birds the resemblance is so close--with the owl and the goose--that there is no character to distinguish the brain of the fossil animal from those of the recent ones. A section of the cerebrum in this specimen entirely corresponds with a section of the brain-cavity in the second skull described, as does the backward extension of the cerebrum with the extent of the cerebral cavity, and the narrow cerebellum with the narrow channel parallel to the walls of the foramen magnum, as in _Gallus domesticus_ and Birds. The front of the brain corresponds with the cast of the front of the cerebral lobes taken from the Ethmo-sphenoid mass. Thus the specimens agree among themselves, and prove the Pterodactyle to have had a brain indistinguishable from that of a Bird. And when it is remembered how distinctive this kind of brain is, and that it approximates rather towards the higher Mammals than towards Reptiles, the fact attains unusual importance in determining the Pterodactyle's place in nature.

?NEURAL ARCH OF SACRAL VERTEBRA, ?VOMER.

Pl. 12.

Frontal(?) Owen. _Palæontographical_, 1859

Pl. 4, fig. 6, 7, 8.

Case. Comp. Tablet. Specimen. =J= _c_ 10 1-3

In 1859 Prof. Owen described with doubt as the Frontal of Pterodactyle, a symmetrical bone. A smaller but more perfect specimen has since been obtained for the Woodwardian Museum; and a fragment of intermediate size is in the rich collection of the Rev. T. G. Bonney. From the descriptions already given it is impossible for it to be the frontal. There is no proof that it is a skull bone. If of Pterodactyle the compressed lateral spaces could only be part of the nasal passages, or the impressions of a palatine or pterygoid articulation. And as the external surface of every specimen is keeled, and as the palatal surface of the upper jaw of every known Greensand Pterodactyle is keeled, and as the concavities slightly converge to the keel, it might be a bone from the under side of the head,--the vomer.

The smallest specimen is a compressed sub-semicircular bone 1-1/4 inch long, 9/16 inch high, and a 1/4 inch thick. The under surfaces converge to form a strong keel, which is flattened off behind. Above this, the posterior third of the bone is compressed obliquely to half the thickness, as though a bone had over-lapped this area on each side. If the oval spaces are nares, that bone might have been the pterygoid or palatine. Three-fifths of the remainder of the bone are taken up by the smooth oval depressions, which might be the inner walls of the nares; and above this is a margin of bone widening into the triangular compressed part in front, which, if the fossil is rightly determined, must have fitted into the posterior end of the maxillary or anterior end of the palatine bones.

A specimen collected by the Rev. T. G. Bonney is preserved on the sacral side of a left _os innominatum_ with the keel downward. It appears to show a sutural surface from which an anterior part has come away. And if this specimen is compared with the neural arch of the sacral vertebra =J=._c_.4.1, it will be found to correspond entirely. It is not impossible that _c_.10.1, 2 may be vomerine, and _c_.10.3 sacral, but there are no distinctive characters between the specimens to warrant such a determination.

QUADRATUM.

Pl. II.

and Quadrato-Jugal.

Case. Comp. Tablet. Specimen. =J= _c_ 11 1-4

In the Woodwardian Museum are two distal ends of the quadrate bone and two other fragments showing the quadrato-jugal with it.

_Quadrate._ The smallest specimen is 1/2 an inch over the articular surface for the lower jaw and a quarter of an inch thick. It is concave from side to side in front where it shows a large pneumatic foramen near the basal end; it is bent from the articulation a little backward. It is convex behind; and between the foramen and the articulation sends inward and forward a great wing like that of the quadratum in birds. The specimens are broken short off and do not show any articulation above, where the bone contracts.

The distal articulation is double, like two long cones placed together; that in front having the base outward, while the hinder one has the base on the inner side. The largest specimen, which is much broken, shows the articulation half an inch thick.

_Quadrato-jugal._ This is a thin flat squamous bone, apparently of a transverse diamond shape, which is anchylosed to the anterior lateral margin of the quadrate, at right angles to the articulation. The lower margin is straight, as is the upper anterior margin, which appears to have received the malar bone above.

The upper posterior side is broken, but shows a large foramen near to the side of the quadrate. The base of the diamond is at the articulation, and at its apex is a small fragment of smooth surface, either part of a foramen, or the orbit of the eye.

In this specimen the articulation, which is broken, is about 3/4 of an inch wide, 3/8 of an inch thick. The remaining piece of the quadrate is an inch long. The quadrato-jugal is an inch and 3/16 high, and between its broken ends 1-3/4 inch long. It is thick and strong where joining the quadrate, but the rest of the bone is about an 1/8th of an inch thick.

The quadrate bone is Avian in possessing a pneumatic foramen, and Avian in the form of so much of the distal end as is preserved, and in the articulation for the lower jaw. The process which it sends inward on the inside is probably for the pterygoid bone, after the manner of Birds. Before anchylosis with the quadrato-jugal bone set in, as may be seen in =J=._c_.11.4, the union was made by a hemispherical knob on the outside of the quadrate, as in _Gallus domesticus_. The squamose quadrato-jugal is a distinctive character.

?PTERYGOID END OF PALATINE BONE.

Pl. 12.

Case. Comp. Tablet. Specimen. =J= _c_ 14 1-2

This determination is conjectural. Its form is such as would make it probable that it is part of the head. A more perfect specimen is seen in =J=._c_.1.2.7.

The best specimen is a compressed sub-quadrate fragment of bone terminating at one end in a long reniform articular surface, and at the other end in a fracture where the bone is rapidly thickening. A side, regarded as the outer one, is flattened, being slightly concave in length, and slightly convex from side to side. The form of the inner side of the bone is determined by the inward curve of the thick part of the articular surface, which sends a rounded ridge obliquely on to the side, so that while it is concave from side to side at the articulation, at the fracture it is convex from side to side. All the specimens are large, the articulation being not less than an inch long.

PREMAXILLARY BONES

Pl. 12.

appear to be developed as in birds. An account of their structure will be found in the notes on the species, page 112.

OS ARTICULARE AND PROXIMAL END OF LOWER JAW.

Pl. 12.

Case. Comp. Tablet. Specimen. =J= _c_ 12 1-6