FREE APPENDAGES — REPTILES 



281 



phalanges, as in marine Chelonia (tig. 308) or by increase in their 

 number (Ichthyosaurs, Plesiosaurs, Pythonomorphs). 



The humerus varies in shape and often has the ent- and sometimes 

 the ectepicondylar foramen (fig. 304) ; it is usually shorter than the 

 forearm. The ulna (often with an olecranon) is usually longer than 

 the radius, these two bones being separate, the arm having slight rota- 

 tory powers. The femur has one or two trochanters, the fibular 

 being most often lacking. Tibia and fibula are separate, the tibia the 

 stronger of the two; its proximal end expanded and occupying most 

 of the articular surface of the femur, the fibula articulating only 

 with the posterior side of the thigh bone. 



Fig. 304. Fig. 305. 



Fig. 304. — Left humerus of Sphenodon (Fiirbringer, 'oo). ec, en, act- and ente- 

 picondylar foramina; Im, Imj, tuberculum minus and majus; re, radial epicondyle; 

 uc, uec, ulnar condyle and epicondyle. 



Fig. 305. — A, forefoot; B, tarsus of Alligator (Gegenbaur, '64). AA, intratarsal 

 joint; c, carpalia; F, fibula;/, fibulare (calcaneus); ic, intracarpal joint; m, metacarpals; 

 R, radius; r, radiale; T, tibia; t, tibiale; //, tritibiale (astragalus); U, ulna; u, ulnare; 

 2—5, tarsalia; I-V, metatarsals. 



The basipodia differ greatly in the various orders, but have the 

 joint of the wrist and especially that of the ankle intracarpal or 

 intratarsal (fig. 305), carpalia and tarsalia lying distal to the hinge. 

 In most existing species tibiale and intermedium form a talus (astrag- 

 alus) and a pisiforme is often present (this having been interpreted 

 as a postminimal digit) and in Ichthyosaurs there are often two or 

 more ossicles in line with it. Typically there are five digits, reduced 

 to three in some Dinosaurs, the three toed feet having led to inter- 

 pretation of the tracks on the triassic rocks of the Connecticut valley 



