The Ornithosauria / An elementary study of the bones of Pterodactyles made from fossil remains found in the Cambridge Upper Greensand, and arranged in the Woodwardian Museum of the University of Cambridge

by H. G. Seeley

The pterodactyle wrist is made up of three bones, arranged as a proximal carpal, a distal carpal, and a lateral carpal. Two of them are figured by Professor Owen, who regarded the distal carpal of this description as the scapho-cuneiform; while A very imperfect example of the proximal carpal is named the unciform: neither of these determinations, the reverse of those which follow, were given as more than probable guesses.

I. Proximal Carpal.

No. 10 shows the proximal surface well; portions of it are seen in Nos. 4, 5, 6, 8, 9, 11, and 12. The distal surface is best exhibited in No. 1; portions of it are shown in Nos. 2, 3, 5, 7, 8. No. 13 is an impression taken from the proximal surface of a distal carpal to show its correspondence with distal surface of the proximal carpal. The bone is proximally of an irregular oblong form, being five sided, and much broader towards the inner end than towards the outer end. The two ends are sub-parallel, and rather obliquely connected on one side by a nearly straight border more than twice as long as the shorter end. The other limits of the sub-parallel ends are connected by two concave borders meeting in a well rounded convexity, which is near to the broader inner end.

The proximal surface of the bone is flattened, and may be divided into a sub-rhomboid space, adjacent to the shorter of the sub-parallel ends, which is moderately concave in the long axis of the bone and slightly convex transversely, and an oblong space adjacent to the longer of the two ends. This is separated from the sub-rhomboid space, toward the straight side of the bone, by an elevated ridge sub-parallel with the ends. It is directed towards the convexity on the opposite side, in which the long and short concave parts meet, but after half crossing the bone it becomes forked in a U shape, and less elevated; the smooth unarticular included space shows an oval pneumatic foramen, which varies in size with the different species. The region between this Y-shaped ridge and the longer of the two ends, is sub-reniform, slightly concave in its long diameter, and deeply concave in the short diameter, exactly corresponding in form with the articular surface already described as the distal end of the ulna. Also parallel with the long end of the bone are marks of an articular surface exactly corresponding with those described as the distal end of the radius; that is, at the convex angle of the angulated side is placed a hemispherical boss,' interior to which is a hemispherical concavity, and extending toward the straight side is the oblique smooth border of the sub-rhomboid area described. There still remains a space to be accounted for. This consists of a sub-quadrate area forming the corner of the bone made by the concave side and the shorter outer end; it is made up of an inner concave part separated from the radial articulation by a ridge, and an outer convex part constituting the shorter end of the bone.

This carpal is moderately compressed from the proximal to the distal side, except towards the shorter end of the bone, being there prolonged distally into a wedge-shaped process, showing at its termination marks of a powerful muscular attachment.

The outer lateral surface is of variable antero-posterior extent.

The distal articular surface is placed entirely toward the narrow end of the bone, leaving at the proximal end a large smooth rhomboid unarticular area, of which every side is a little concave: it connects obliquely the proximal with the distal articular surfaces. The distal articular area is divided by a diagonal ridge into a long oblong area of which the inner and outer sides are sub-parallel and the ends rounded: it is slightly concave in length as well as transversely, and is slightly twisted like the flukes of a screw. Adjacent to this region laterally is the other and sub-triangular part of the articulation. The broad end of the triangle is toward the broad end of the bone; it is concave in length and flattened transversely. The two parts of the articulation are inclined to each other at a large angle, both looking downward and outward, but on opposite sides of the bone.

II. Distal Carpal.

The tablets of this bone comprise 22 specimens. Nos. 2, 3, 4, 5, 6, 8, 9, 10, 15, 16, 19 and 22 are so mounted as to exhibit the proximal surface. Nos. 7, 11, 12, 13, 14, 15, 16, 20 and 21 show the distal surface of the bone. No. 17 is a cast from the distal surface of a proximal carpal for comparison with the proximal surface of the distal carpal. No. 16 is a cast from the proximal end of the wing-metacarpal for comparison with the distal surface of the distal carpal. No. 20 is a distal carpal of unusual type, 19 is a cast from its proximal surface, and 21 is a cast from the distal surface of the same specimen.

The proximal aspect of this bone is rather narrower than the distal aspect; each is sub-triangular in outline, the sides being convexly curved. In the long axis from the apex on the inside to the short outer[Q] side the bone is convex proximally with an oblique transverse depression; in the short axis, that is, between the two longer sides, the middle of the bone is hollow, but the oblique transverse depression makes both sides of the hollow convex,—so that excepting the smooth unarticular triangular area adjacent to the apex, the sub-quadrate articular surface is shaped somewhat like two cones put side by side in such manner that the apex of each touches the base of the other: the apex of that cone which should touch the short side or base of the triangle formed by the bone, is truncated by a depression which exhibits an oval pneumatic foramen. Towards the apex, on the same side as the pneumatic foramen, the margin of the bone is rounded for a small terminal oval articulation which looks outward and upward.