LIMBS 



163 



Reptiles. In existing Reptiles as a general rule the 

 body is only slightly raised from the ground in locomotion, but 

 in some the limbs serve as more highly organised organs of 

 support, and in certain of the Dinosauria the hind limbs were the 

 main organs of progression. The fore limbs in such cases tend to 

 take on other functions, and in the flying Pterosauria the fifth 

 finger was produced into a long, jointed rod which supported a 

 wing-like expansion of the integument. 



Chelonians, and more particularly Hatteria, come nearest to 

 the Urodeles in the structure of the carpus. 1 Five digits are 

 usually present in Reptiles in both manus and pes, and traces also 

 of the former possession of an extra ray both on the radial and 



FIG. 125. CARPUS OF A, Hatteria punctata, AND B, Emydura kre/lii. 

 ^ (After Baur.) 



f 1 , radial centrale ; c 2 , ulnar centrale ; i, intermedium ; p, ulnar sesamoid 

 (pisiform) ; #, radius ; r, radiale ; U, ulna; u, ulnare ; 1 5, carpalia ; IV, 

 metacarpals. 



ulnar side ("pisiform") can usually be recognised (Figs. 125 

 130). The tibia and fibula always remain separate. 



In Lizards and Crocodiles the carpus and tarsus diverge more 

 from the primitive form. In the latter, which, like Anurans, 

 possess no trace of an intermedium, the proximal row of the 

 carpus consists of two hour-glass-shaped bones a larger radiale, 

 and a smaller ulnare (Fig. 128). The centrale, as in Anura, comes 

 to be situated in the distal row, which, like the fourth and fifth 

 digits, is much reduced. 



In Ichthyosaurus and Plesioeaurus the limbs were modified to 



1 In Hatteria and certain Chelonians, as well as in the extinct Proterosaurus, 

 a double centrale is present in the carpus, and more or less distinct traces of a 

 double condition of this element are seen in certain other Chelonians. Indica- 

 tions even of a third centrale occur in Hatteria. 



M 2 



