In no other reptiles has there been as great modification of the fingers as in the Pterosauria (Fig. 142), so great indeed that there is dispute as to the homologies of the ones that remained. The maximum of changes was reached in the latest forms, especially Nyctosaurus and Pteranodon, where there are three very short and weak fingers on the preaxial side, with two, three, and four phalanges, the terminal ones in the shape of strong claws. On the postaxial side the fourth finger is very long and strong, with four phalanges for the support of the patagium. This wing finger has generally been supposed to be the fifth, the first finger or pollex represented by a slender bone turned backward from the wrist toward the humerus and known as the pteroid. It seems more probable that the wing finger is the fourth, as originally so called by Cuvier, the fifth being absent. In the development of the patagium the claw of the wing finger would in all probability disappear, as in the bats, leaving the normal number for the fourth digit. If it is really the fifth, not only has the claw been converted into a long membrane-supporting phalange, but an additional phalange has been added; while each of the preceding three digits has lost one phalange. We can conceive of no cause for such hypo- and hyper-phalangy in the hand in these volant reptiles. One of the phalanges of the third finger is short, as in the third digit of the foot.
The first three metacarpals of the early pterodactyls articulated normally with the carpus (Fig. 142); in the later ones they were mere splints lodged loosely in the flesh at the distal end of the fourth metacarpal, only the first of them retaining a very slender connection with the wrist. The fourth metacarpal, on the other hand, progressively increased in length till it much exceeded the length of the forearm. Its distal articulation is a very perfect pulley-like joint, permitting flexion of the first phalange through almost one hundred and eighty degrees.
A general reduction of the postaxial digits of both front and hind feet is characteristic of the Dinosauria (Figs. 141, 156). Only in the primitive Anchisaurus and Plateosaurus (Fig. 141 a) is a nearly complete hand recognized, and even in these, two phalanges of the fifth finger are gone. The fifth finger is absent in all Theropoda since the early Jurassic, the fourth usually, the third sometimes. In Gorgosaurus (Fig. 141 c), from the uppermost Cretaceous, the hand is func-
