FREE APPENDAGES — REPTILES 



283 



ICHTHYOSAURIA alsos how a progressive modification of the appendages, 

 the earher species having more normal limbs, the later being more paddle-like 

 (fig. 306). In the latter radius and ulna are short and stout, the humerus having 

 concave facets for articulating with the antebrachial bones. The carpus is 

 incompletely ossified, the bones having an outer coat of cartilage. The pisiforme 

 has two or three bones in line with it. A few species had but three digits, but in 

 many there is a dupUcation of digits already referred to (p. 282). The femur is 

 relatively longer than the humerus and has similar articular facets. In other 

 respects the two hmbs are much ahke, the hinder being the smaller. 



U 



Fig. 306. — Fore limb of 

 Leptocheirus (Merriam, 

 '03). h, humerus; r, 

 radius; n, ulna. 



Fig. 307. — A , fore limb and B, hind limb of Spheyiodon 

 (Osborn, '03) ; C, carpus of developing Sphenodon (Schau- 

 insland, '03). c, centralia; F, fibula; /, fibulare; H, 

 humerus; i, intermedium; R, radius; r, radiale; T, tibia; 

 t, tibiale; U, ulna; n, ulnare; I— V, metacarpals or meta- 

 tarsals; 1-5, carpalia or tarsalia. 



Rhynchocephalia. — In Sphenodon and the more typical fossil 

 genera the short humerus (fig. 304), expanded__^at both ends, has both 

 epicondylar foramina, but some fossils have only that on the ulnar 

 side. Usually the carpus is primitive and Sphenodon (fig. 307) has 

 radiale, intermedium and ulnare, and in the embryo three centralia 



