PHYLUM CHORDATA 



329 



. P7i f 



FIG. 938. Tarsus of Emys europeea 



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

 tibia; fi)f.t. c. the united tarsals of the 

 proximal row ; Pk'. first phalanx of the 

 fifth digit ; 1 4. distal tarsals ; / J", 

 metatarsals. (From Wiedersheim.) 



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 



are 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 svm- 



c/ 



physes. In the tarsus (Fig. 

 938) there is a single proximal 

 iDone, and four distalia. 



In the Crocodilia also the 

 clavicle is absent, but there is 

 an episternum. There are two 



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

 form (j-) 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-scaplwicl 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) ; 

 thev are never embedded in sockets in 



*/ 



any recent form. A Mexican Lizard, Heloderma, 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.) 



