XIII 



PHYLUM CHORDATA 



329 



-Ph 



FIG. 938. Tarsus of Emys europsea 



(right side) from above. F. fibula ; T. 

 tibia; (i)f.t.c. the united tarsals of the 

 proximal 'row ; Ph'. first phalanx of the 

 fifth digit; 14. distal tarsals; IV, 

 metatarsals. (From Wie.dersheim.) 



structure of which the most ventral and posterior ray, ending in a free 

 extremity, is the coracoid ; while the other two are the pro-coracoid 

 (or clavicle) and the scapula, 

 with the supra-scapula, which 

 ^re fused at their glenoid ends. 

 The bones of the carpus have 

 the typical arrangement, con- 

 sisting of a proximal row of 

 three, a distal row of five, and a 

 centrale between the two. The 

 pelvis resembles that of Lacer- 

 tilia, except that it is broader 

 -and shorter. Both pubes and 

 ischia meet in ventral sym- 

 physes. In the tarsus (Fig. 

 938) there is a single proximal 

 bone, and four distalia. 



In the Crocodilia also the 

 clavicle is absent, T)ut there is 

 ^,n episternum. There are two 



proximal carpal bones (Fig. 939), and two distal. There is pisi- 

 form (]*) sometimes considered as a rudiment of a sixth digit. The 

 pubes and ischia (Fig. 940) are fused ; both meet in symphyses, the 

 apposed ends being cartilaginous. The 

 acetabular portion of the ilium is ossified 

 as a distinct bone. In the tarsus (Fig. 941) 

 there are two proximal bones an astra- 

 galo-scaphoid and a calcaneum the latter 

 having a prominent calcaneal process ; and 

 two distal tarsal bones, together with a 

 thin plate of cartilage supporting the first 

 and second metatarsals. The missing 

 fifth digit is represented by a rudimentary 

 metatarsal. 



Digestive Organs. The form and 

 arrangement of the teeth already de- 

 scribed in the account of Lacerta prevail in 

 the majority of Lizards. In some of them 

 the palatine teeth are absent. The teeth 

 are sometimes fixed by their bases to the 

 summit of the ridge of the jaw (acrodont 

 forms), sometimes fixed by their sides to 

 the lateral surface of the ridge (pleurodont); 

 they are never embedded in sockets in 

 any recent form. A Mexican Lizard, Eeloderma, differs from 

 all the rest in having teeth which are grooved for the ducts 

 of poison-glands. In the Snakes (Figs. 932, 933) teeth are 



FIG. 939. Carpus of young 

 Allierator. R. radius ; 

 U. ulna ; C. centrale ; r. 

 radiale ; u. ulnare ; 1 5, 

 the- five distal carpals (not 

 yet ossified); 1 and 2 

 united into one, and also 

 3, 4 and 5 ; t, pisciform ; 

 / V, the five metacarpals. 

 (From Wiedersheim.) 



