In its long diameter the articulation is a little convex; transversely it is very convex in the ovate part, but more flattened in its narrower continuation. Where widest it measures about 4/10ths of an inch.
Nos. 5 and 6 on another tablet appear to be distal ends of ulna of another kind of Pterodactyle. They are less compressed, more quadrate in section, and have the sides more nearly parallel The flattened side similarly has a concave border, but instead of having its distal termination developed laterally, has it thickened behind. The opposite side of the bone which in the other specimens was compressed is here thick and well rounded, and not at all inflected. There is an absence of the concavity noticed on the outer surface of the bone in the compressed specimens. The articular surface is much flatter, and a little concave in length instead of being convex; as in the other examples it looks downward. The largest fragment. No. 5, measures 13/8 inch long; it is 6/8 inch wide at the fracture, and 4/8 inch thick. The sub-quadrate distal end is more than an inch long, more than 4/8ths inch thick on the thick side, and nearly 4/8ths inch thick on the compressed side.
II. Distal End of Radius.
The best preserved of the 10 specimens here exhibited is 3 inches long, No. 2. The shaft is oval, flattened on one side; measuring at an inch from the fractured end 7/10ths of an inch in the least diameter, and one inch in the wide diameter. It widens distally at first slowly, then rapidly, till at the articular end its greatest width is two inches. But while expanding laterally it contracts from side to side, the more convex side of the two at about an inch from the articular end, beginning to approximate to the flatter side till the articular end has a short diameter of less than half an inch.
On the left-hand corner of the convex inner side of the bone is an elevated flattened disc for muscular attachments, fully half an inch in diameter, there is a slight muscular attachment interior to this, nearer the middle of the bone. The left-hand corner of the flattened outer side of the distal end of the radius is marked by a vertical ridge bordering a similarly elevated oval muscular attachment. Parallel to this nearer the middle of the side is a much stronger and acutely elevated ridge.
The articulation is made up of three distinct parts, all in a straight line. The portion of bone adjacent to the large muscular disc is compressed and rounded on the distal end; then first there is a rather deep circular cup 3/8ths of an inch wide, nearer to the more convex than to the flatter side of the bone; adjacent to this cup is a convex ball of about the same size; while the remainder of the articulation is concave in length, convex from side to side, and looks downward and a little towards the inner convex side of the bone. The specimens are arranged so as to display these characters.—The example described is of nearly the same size as that figured for the humerus in fig. 1, T. XXIV. of the Cretaceous Reptilia. The less well preserved bone in that figure exhibits the Ulna in its true position behind the Radius.
III. Proximal End of Ulna.
This bone has much the proportions of the Ulna in birds, the smaller specimens nearly resembling the ulna of the Heron. The specimen (No. 1) with the shaft best preserved is 21/4 inches long, cylindrical at the fracture, where it measures in diameter 3/16ths of an inch. It gradually enlarges proximally widening to about 7/10ths of an inch; near the proximal end it is a little curved, the side which is concave in length being a little flattened, while there is a lateral elevation on the opposite side, apparently corresponding to the quill-ridge on the convex side of the bird-ulna. There is a separate ossification for the olecranon, which is an irregular sub-oblong bone forming the outer part of the articulation; it is only preserved in No. 1. Nos. 4, 5 and 6 show the concave transverse groove from which it has come away.
The articular surface looks upward and forward, in which aspect it has a trapezoidal form. Sometimes, as in No. 2, the great sigmoid area is divided into two parts by a vertical ridge, the more elevated part of the articulation on the radial side of the bone being concave, while the outer part, as in the heron, besides being concave, has its border on the concave side of the bone produced and rounded. There is a small triangular elevation on the radial aspect of the proximal end like that on the corresponding part of the ulna of the heron. On this aspect the bone is flattened, on the opposite and outward aspect it is compressed and produced as in the bird. No. 2 measures 11/8 inch over the articular end. The series includes 6 specimens.
IV. Proximal End of Radius.