Sub-cylindrical bones, apparently elongated, and a little compressed obliquely, terminating distally in a slightly expanded trochlear articulation. Some of them show on one side marks of an osseous adhesion: this has led to their being regarded as claw metacarpals rather than as the distal ends of tibiæ. But on the supposition of their being claw metacarpals, they are as compared with the same bones in Pt. Suevicus, out of all proportion large, since wing-metacarpals from the Cambridge Greensand would not as a rule have a diameter more than twice that of these bones. The trochlear articulation is smaller in proportion to the shaft than in the wing-metacarpal, and usually shows a pit at the side and grooves above for ligaments; the mesial pulley groove is shallow and broad. Seven specimens are mounted in illustration, of which No. 3 may be regarded as doubtful. It is possible that they may be metatarsals.
| Case. | Comp. | Tablet. | Specimen. |
| J | b | 8 | 1—3 |
CLAW PHALANGE.
[Pl. 8.]
These three sub-triangular bones, which supported the claws, are much compressed from side to side, and consequently deep. The superior outline is convex from front to back and rounded from side to side. The inferior outline is concave from front to back, sometimes narrower, sometimes broader than the upper part of the bone, while the inferior aspect is always more flattened than the superior aspect. On each side on the lower half of the bone is a deep groove. The articular end is divided into an upper articular part, which extends as far down as the lateral groove and a lower non-articular part with ligament markings. The articulation is concave from above downward, and is divided into two lateral parts by a mesial vertical ridge. The articular end is about half as deep as the bone is long.
| Case. | Comp. | Tablet. | Specimen. |
| J | b | 10 | 1—9 |
Pelvic Girdle and Hind Limb.
OS INNOMINATUM.
[Pl. 8.]
Nine specimens are mounted in illustration of the pelvic girdle: Nos. 1, 3, 4, 5 and 6 show the acetabular or femoral aspects. The right os innominatum is exemplified by Nos. 1, 4 and 5; the left by Nos. 3 and 6. No. 2 shows the sacral aspect of a left ischium, and its attachments with the pubis and ilium. No. 8 is the sacral aspect of a left os pubis. No. 9 is the femoral aspect of a right OS pubis. None of the specimens are sufficiently complete to give the form of any of the bones. The only known example of an entire or nearly entire pelvis at all comparable in form, is seen in the original specimen of Dimorphodon macronyx figured by Buckland, Trans. Geol. Soc. Ser. 2. vol. III. p. 217. In nearly all the fossils from the Cambridge Greensand the bones of the pelvis are anchylosed together.
The ossa innominata have been determined as right and left on the supposition that the pelvis of the Dimorphodon is in situ, and from the general correspondence of the form of the constituent elements with elements of the pelvis in the lower mammals, reptiles, and birds.
Each os innominatum shows a hemispherical acetabulum which is slightly elongated in antero-posterior extent In the Dimorphodon the bone which is superior to the cup, that is to say, which extends dorsally along the sacral vertebræ is prolonged anteriorly as a strong narrow straight style, the base of which is seen in the parts marked Ilium in Nos. 1 and 6. A more perfect example may be studied in a pelvis from the Cambridge Greensand preserved in the collection of the Geological survey. Posterior to the acetabulum a similar but stronger bony style extends for more than the length of the acetabulum, curving slightly downward at its posterior part. The dorsal outline of this portion of the bone is slightly concave. The posterior horn like the anterior horn forms part of the ilium which constitutes the upper half of the acetabular cup. The os innominatum contracts in antero-posterior extent below the acetabulum, and immediately widens again in a thin concave bony expansion. The anterior or pubic outline is comparatively straight, and at right angles with the ilium; the posterior or ischiac outline is deeply cupped where the ischium unites with the ilium, and becoming straight extends backward at a considerable angle. The ischium contributes less to the pelvic cup than either the ilium or pubis; it is flat in front and convex on the visceral side, rounding into the narrow flattened posterior side. The pubis is separated from the ischium by a suture extending vertically through the obturator foramen. The obturator foramen [seen in No. 9] is small and oval, less than half the diameter of the acetabulum, situated below its ventral border. It passes obliquely downward and a little forward, and its opening makes the exterior aspect of the pubis concave; the visceral aspect of the pubis is convex from side to side like the ischium. The sacral aspect of so much of the os innominatum as is seen, is concave from the dorsal to the ventral margins, and is cupped behind and below the acetabulum, the surface being rough. Among reptiles the ilium is chiefly behind the acetabulum, in mammals it is chiefly in front. In the over-lapping group, Aves, it extends both ways. Among the Amphibia the ilium is chiefly anterior to the acetabulum. In Crocodiles it has a slight extension both ways, in Dinosaurs the extensions are more marked and the whole arrangement approximates to birds. But among animals which have been affiliated with reptiles the Dicynodonts are the only order in which there is a pelvis so mammalian and massive. If the ilium of the Monotreme genus Echidna had a posterior extension, the pelvis would be altogether comparable with the pelvis of this Pterodactyle, and would differ chiefly in the larger obturator foramen, the perforated acetabulum and the unanchylosed condition of the pelvic elements. The pelvis of Apteryx does not make any near approximation.
Moreover specimens Nos. 3 and 4 show on the anterior pubic border, about the base of the acetabulum, a slight pit or roughness to which something has been attached, and in the original specimen of Dimorphodon associated with the pelvis are two triangular bones which recall something of the form of the prepubic bones of Echidna. Most German Pterodactyles show on the OS pubis an enormous prepubic bone. In Iguana the pubis forms at its anterior border, a sharp angular process. In Chelydra the process is long and narrower, and arises from the middle of the border. In Echidna this prepubic process has become a distinct prepubic bone and is more elongated. Unlike the marsupial bones it is attached to the pubis by a wide base. The anterior pubic roughness of Cambridge specimens, and the loose bones of the Dimorphodon, &c. indicate the existence of structures in the Ornithosauria homologous with the prepubic bones of the Ornithodelphia.