17G 



ANATOMY OF VERTEBRATES. 



53, is more expanded at its proximal end than in the Crocodile or 

 Lizard ; the inner (ulnar) tuberosity is more prominent, the radial 

 crest much more developed : with a base coextensive with one 

 fifth of the shaft of the bone, it extends in a greater proportion 

 from the shaft, affording a powerful lever to the muscles inserted 

 into it. The articular head is reniform. The shaft is cylindrical: 



ill 



Skeleton of Pterodactylus crassirostris. A. Restoration of Pterodactyle. clxxx. 



the walls thin and compact, the cavity large, and was filled with 

 air as in birds of flight. l 



The ' pneumatic foramen,' or that by which the air passed from 

 a contiguous air-cell into the bone, is situated on the fore (palmar) 

 side, a little below the radial end of the head of the bone. The 

 radius, ib. 54, and ulna, ib. 55, are very long, straight, and closely 



connected together. 



The dibits show the lacertian number of 



1 cxlix. p. 16. i. xxvi. p. 451. This discovery breaks down the following 

 distinction : ' Au reste, on distingue toujours l'humerus d'un lezard de eelui d'un 

 oiseau, parceque le premier ii'est pas creuz ni perce de trous pour l'entree de Pair 

 dans son interieur.' cli. v. pt. 2, p. 296. 



