196 THE OSTEOLOGY OF THE REPTH^ES 



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 maxi- 

 mum of changes was reached in the latest forms, especially Nycto- 

 saurus 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 sup- 

 port 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 probabihty disappear, as in the bats, leaving the normal num- 

 ber 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 meta- 

 carpal, 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 com- 

 plete 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 Gorgo- 

 saurus (Fig. 141 c),from the uppermost Cretaceous, the hand is func- 



