xm 



PHYLUM CHORDATA 



343 



PW 



Pythons vestiges of hind-limbs, ,are to be detected in the form of 



two or three small bones which support a small horny claw. 

 In Sphenodon (Fig. 995) there 



is a foramen above the outer 



and one above the inner condyle 



of the humerus. There are eleven 



carpal elements, of which there are 



four, including a pisiform, in the 



proximal row, two centrals, and 



five in the distal row. The pubes 



are united in a symphysis, in front 



of which is a cartilaginous epipubis. 



A large oval foramen intervenes 



between the ischium and the pubis. 



A cartilaginous Tiypo-ischium is 



attached to the ischia behind. In 



the tarsus the tibial and fibular 



elements are distinct, though firmly 



united. The intermedium and the 



centrale are firmly fixed to the tibiale. 



tarsal bones. 

 In the Chelonia (Fig. 997) the interclavicle (episternum) and 



clavicles are absent, unless, as is probable, the former be represented 



by the median element of the plastron and the latter by the first 

 a/ lateral pair. The entire pectoral arch is a 



tri-radiate structure of which the most 

 ventral and posterior ray, ending in a free 

 extremity, is the coracoid ; while the other 

 two are the scapula and a process, sometimes 

 regarded as representing the procoracoid, 

 given off on the inner side of the scapula 

 near its glenoid end. The bones of the 

 carpus have nearly the typical arrangement, 

 consisting, as in Lizards, of a proximal row 

 of three, a distal row of five, and a centrale 

 between the two. The pelvis resembles 

 that of Lacertilia, except that it is broader 

 and shorter. Both pubes and ischia meet 

 in ventral symphyses, and epipubic and 



FIG. 1006. Tarsus of Emys europaea 

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

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

 proximal row ; Ph'. first phalanx of the 

 fifth digit ; 14, distal tarsals ; I V, 

 metatarsals. (From Wiedersheim's Com- 

 parative Anatomy.) 



There are three distal 



/ 



' I 



1 



p 



# 17 



FIG. 1007. Carpus of young 

 Alligator. C. centrale (?) ; 



R. radius ; U. ulna ; 

 diale ; u. ulnare ; 1 </, U1C 

 five distal carpals (not yet 



tie: i*. ulnare; i-s, the nypo _i sc hial cartilages may be 'present. In 



ossified) ; 1 and 2 united into 

 one, and also 3, 4, and 5 

 t, pisiform ; IV, the five 





the tarsus (Fig. 1006) there is usually a 

 single proximal bone and four distalia. 

 There are never more than two phalanges in 

 any of the digits. 

 In the Crocodilia also the clavicle is absent, but there is an epis- 

 ternum. The number of carpal elements is reduced, the largest 

 being two proximal bones, the radiale and the ulnare (Fig. 1007, r, u). 



Y 2 



