FREE APPENDAGES AMPHIBIA 



279 



but at least in many cases the radial or tibial side of the appendage is 

 first to show reduction, the fifth digit following. 



AMPHIBIA. — The most primitive known Tetrapod limbs are 

 those of Stegocephala; those of Urodeles, where the limbs still extend 

 at right angles, are scarcely less primitive, the modifications being 

 largely loss of parts. The posterior appendages of Anura have 

 undergone the greatest modifications in connexion with their leaping 

 habits. Siren (a Urodele) has lost the hind legs; while Gymnophiona 

 and Aistopod Stegocephals have lost both pairs. All recent Amphi- 

 bia have, at most, but four digits in the 

 manus, unless parts in the Anura (p. 280) 

 be remnants of pollex and prepollex. 



Stegocephala have stout limbs, the 

 humerus rarely with an ulnar (entepicondylar) 

 foramen. Ulna and radius, tibia and fibula 

 are never fused. The carpal elements are 

 often unossified, but some species have two 

 and even three centralia in the carpus. Most 

 species have four digits in the manus, a few 

 have five. The hind Hmbs are always penta- 

 dactyle, the second or third digit being the 

 longest. 



Urodela (fig. 302, A, B, D) have 

 a relatively long humerus, ossified, 

 usually, only in the shaft. It has radial 

 and ulnar tuberosities for retractor and 

 protractor muscles. Ulna and radius 

 are separate, about equal, can be 

 shghtly rotated, and the ulna has an 

 olecranon. The carpus is slightly 

 ossified in Perennibranchs and some 

 other genera. In the more typical species there are seven or eight 

 slightly ossified carpal bones, including one (or two, proximal 

 and distal) centralia and four carpaha. When, as in Proteus and 

 Amphiuma, the digits are reduced to three, fusion of radiale and 

 carpale 2, intermedium with carpaha 3 and 4, reduces the number of 

 separate elements to three. It is not settled which digit is lost, 

 probably i in all genera. No recent Urodeles have lost both 

 pairs of legs, but apparently this was the case in the extinct 

 Lysorophus. 



Fig. 302. — .4, carpus of Crypto- 

 branchus; B, of Triton larva 

 (Gegenbaur, '64); C, Geolriton 

 (Baur, in Cope, '89); D, fore leg of 

 Diernyctylus. c, centrale; F , fibula; 

 /, fibulare; H, humerus; i, inter- 

 medium; w, metacarpals; 7?, radius; 

 r, radiale; U, ulna; u, ulnare; 1-5, 

 carpalia or tarsalia. 



