LIMBS 



129 



(Chelonians), and partly with the corresponding metatarsals 

 (Lizards) ; thus there is an increasing tendency for the move- 

 ment of the foot to take place by means of an intertarsal articula- 

 tion, as in Birds. 



In Crocodiles there are two bones in the proximal row of the 

 tarsus, one of which corresponds to a tibiale, intermedium, and 

 centrale, the other to a fibulare. The former is spoken of as the 

 astragalus, the latter as the calcaneum, and on it a definite heel 

 {calcaneal process) is seen for the first time in the a.nimal series. 



Fig. 108. — Right Carpus of Emys 

 europcea. (From above. ) 



i?, Radius ; U, ulna ; r.c, fused radiale 

 and centrale (or centrale 1 and 2, 

 Baur) ; i, intermedium ; u, ulnare ; 

 1-5, the carpalia, of which 4 and 

 5 have become fused together ; t 

 (radiale, Baur) and *, elements 

 on the radial and ulnar side res- 

 pectively, indications of additional 

 radial and ulnar (pisiform) rays ; 

 I-V, the metacarpals. 



Fig. 109.— Left Carphs of 

 Lacerta agilis. (From 

 above.) 



R, radius ; U, ulna ; ii, ul- 

 nare ; i, intermedium ; r, 

 radiale, formed by the 

 fusion of two elements, 

 one of which corresponds 

 to a prepoUex ; c, cent- 

 rale ; 1-5 ; carpalia ; f, 

 ulna sesamoid (pisiform); 

 /- V, the metacarpals. 



The distal row consists originally of four small cartilages, but these 

 later undergo a partial fusion. 



The number of phalanges on the fourth and fifth digits in the manus is 

 greater in the embryos of Crocodiles than in the adult. This indicates that 

 the CrocodiUa have been derived from forms possessing a fin-like fore-limb. 



In Ichthyosaurus and Plesiosaurus the limbs are modified to form paddles, 

 the digits consisting of numerous phalanges, and additional rays being present 

 in the former genus. In Pterodactylus and Bhamphorhynchus the fourth finger 

 was produced into a long jointed rod, which supported a wing-like expansion 

 of the integument. 



Amongst the Lacertilia, various degrees of reduction of the extremities 

 may occur, and in certain Snakes {e.g., Python) traces of the hind-limbs exist. 



Birds. — The fore-limb of Birds is considerably modified by 

 adaptation for flight. The manus loses its primitive character and 

 undergoes reduction, while the brachium and antibrachium, as 



K 



