702 S. W. WILLISTON 



but four phalanges, one less than the normal number, and quite 

 that of the crocodiles; that is, as I have previously urged, it lacks 

 the claw. In the acquirement of a membrane-bearing function this 

 is precisely what would be expected in any finger, and is what 

 occurs in the bats, as Abel has said. That the claw gradually 

 elongated, changing its function from prehension to supporting, 

 seems highly improbable. This finger then answers all the require- 

 ments for the fourth. If, on the other hand, in consonance with the 

 Goldfuss theory, it is the fifth digit which acquired the membrane- 

 supporting function, not only must the claw have changed its 

 function and become elongated but a new phalange must have been 

 added to the finger. Although among aquatic reptiles hyper- 

 phalangy is a common characteristic, we know of no instance among 

 terrestrial vertebrates that I can recall where an additional phalange 

 has been acquired, in either the front or the hind feet. And, if the 

 Goldfuss theory be true, not only must there have been hyper- 

 phalangy in the fifth digit, but hypophalangy in the four preceding 

 digits; that is, in the acquirement of a wing function, an increase 

 and loss of phalanges must have occurred concurrently in the hand. 

 I cannot believe that this was the case. Had we not to deal with 

 the peculiar bone called the pteroid, articulating with the carpus 

 and turned backward toward the elbow, the question of the homol- 

 ogy of the wing-finger would doubtless never have been raised. 



It is the pteroid, then, which has caused all the dispute, from the 

 necessity of accounting for the bone, which, other than a misplaced 

 first metacarpal, seems inexplicable. Two derivations have been 

 imputed to it, as a sinew bone, and as a sesamoid bone. In favor 

 of its being merely an ossified sinew is the fact that, in the remark- 

 able specimen I have described of Nyctosaurus, seven well-ossirled 

 tendon bones are seen lying by the side of the forearm and hand, 

 elongated bones with one end flattened and the other attenuated. 

 In favor of the latter view that it is merely a sesamoid bone 

 developed in the tendon of some carpal muscle originally is the fact 

 that sesamoid bones do occur elsewhere in the pterodactyls. In the 

 above-mentioned specimen of Nyctosaurus I found one lying over 

 the end of the radius and another over the outer end of the coracoid; 

 and I have seen them often in Pteranodon. Sesamoid bones have 



