LIMBS. 



105 



come fused together, and the intermedium is wanting. The proximal 

 row of the tarsus, moreover, consists of only two cylindrical bones, 

 which are usually united together by an envelope of cartilage. 

 One' of these corresponds to a tibiale plus intermedium, and is 

 called the astragalus; the other or calcaneum answers to a 

 fibulare (Fig. 90, Aa, Co). 



In the distal row there are as a rule four separate elements. 

 Rudiments of a fifth carpal, as well as of an extra digit on the radial 

 side, are usually present, and traces of an extra toe are also seen on 

 the tibial side of the tarsus. 



In Anura, the metatarsals and phalanges, between which the 

 web of the foot is stretched, are very long and slender. The femur, 

 as well as the bones of the shank, which are fused together, are 

 also exceedingly long, in correspondence with the mode of 

 progression of these animals. 



The skeleton of the extremities is more strongly ossified in 

 Anura than in Urodeles, in which many of the elements remain 

 cartilaginous. 



Reptiles. Chelonians and Lizards closely resemble Urodeles 

 in the structure of the carpus, and here also traces of the 



Ji if 



FIG. 91. RIGHT CARPUS OF A YOUNG Alligator Indus. (From above.) 



R, radius ; U, ulna ; r, radiale ; u, ulnare ; C, centrale ; 1 to 5, the five carpalia, a 

 yet unossified, of which 1 and 2, as well as 3, 4, and 5, have become fused 

 together ; f, pisiform ; / to V, the five metacarpals. 



former possession of an extra finger on the radial side are to be 

 seen. The tibia and fibula always remain separate. 1 



In Crocodiles, which 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. 91). A rudiment 

 of a sixth ray is present on the outer side of the latter, and this 



1 In Hatteria alone, amongst existing Reptiles, a double centrale is present in the 

 young animal. 



