This bone terminated in an epiphysis which formed part of the articular surface, and has disappeared from all the 7 specimens mounted. So much of the articulation as remains does not oppose the idea of its having been attached to the humerus, while the large size of the example No. 7, which could not have measured less than 21/2 inches from side to side over the articulation, is more in accordance with what is at present known of the dimensions attained by the distal end of the humerus than with the size that would be expected in the distal end of the tibia, which is the only other unknown bone to which these specimens could be referred.
The longest specimen, No. 3, is 3 inches long; broadly ovate at the fracture, measuring in the long diameter 1 inch, and in the short diameter more than 3/4ths of an inch. Nearer the articular end the bone becomes in section sub-quadrate or rather sub-rhomboid. No. 1 shows these terminal characters extremely well. On the posterior aspect of the specimen the surface is divided into two flattened slightly convex parts by a median vertical well-rounded angular bend. In front the side is similarly divided into two parts, both of them a little concave proximally, by a sharp median vertical ridge, which does not reach to the articulation by a varying distance, never so long as the bone is wide. The ridge terminates in, and is pierced by, a vertical groove apparently for a nutritive vessel. Where the anterior and posterior aspects of the bone converge laterally the sides are well rounded.
Only a small part of the articular surface is preserved, looking upward and a little forward; it terminates the wider of the halves of the bone laterally and in front. The remainder of the articular surface, from which the epiphysis has come away, may be divided principally in the majority of specimens into a posterior flattened median rhomboid space and an oblong cup-shaped anterior space divided from it by an elevated ridge. The extreme lateral termination appears to have been a ball-shaped convexity.
The great length of the fore-arm relatively to the humerus, characteristic of German Ornithosaurians, from the fragmentary condition of Cambridge specimens is not seen.
Although the fore-arm resembles Chrysochloris in plan the resemblance is not close in the details of form. In many Mammals it is characteristic for the radius to be the principal bone of the fore-arm, and among Ruminants in which this is especially the case the radius is altogether in front and the ulna behind as is the position with Birds and Crocodiles. And among mammals with claws, as in the Lion, Bear, &c., and in the Chameleon, it is characteristic, for the radius also to be on the inside of the limb at the distal end, as in Ornithosaurians. In form, ridges, and muscular attachments (see pl. 3) the distal end of the radius approximates closely to the Bear and the Lion, and may also be compared with the Bats and Birds, though with Birds it is a small bone. From the epiphysis of the proximal end apparently being wanting it would be difficult to compare closely. But though not like any particular mammal, it might have pertained to a mammal since it has the large perforation for the nutritive vessel near to the proximal end as in the Camel and many of the mammalia.
The ulna of the Pterodactyles is at the proximal end altogether distinguished from mammals by the slight development of the olecranon, nor can the distal end, especially in its relation to the carpus, be paralleled.
Among birds and reptiles the ulna is the large bone, and here a general resemblance in form to the ulna of Pterodactyles is seen at the proximal end. It is not compressed from side to side as in the Crocodile, Iguana, Monitor, &c., but from back to fronts in this rather resembling Birds than the Chameleon. It however at the distal end is more crocodilian.
The fore-arm in plan is mammalian. The Pteroid bone is mammalian, the Radius is mammalian and avian; the Ulna is avian, and crocodilian in form, but mammalian in proportion. The pneumatic foramen of the ulna is peculiarly avian.
| Case. | Comp. | Tablet. | Specimen. |
| J | b | 1 | 1—13 |
| 2 | 1—18 | ||
| 3 | 1— 4 | ||
| 4 | 1— 8 |
CARPUS.
[Pl. 5.]