THE LIMBS 



183 



Very interesting are the modifications of the wrist and hand in the 

 marine Crocodilia (Fig. 150). But two carpals remain, correspond- 

 ing to the elongated ossified bones of the terrestrial forms; the first 

 of them, the supposed radiale, is very broad and flat. 



The carpus and hand of the 

 strictly aquatic or marine reptiles 

 are so like the ankle and foot 

 that they may be discussed to- 

 gether (p. 193). 



Tarsus 



The earliest known tarsus is 

 that of Eosauravus (Fig. 151 b), 

 presumably a cotylosaur reptile, 

 though the skull is not known, 

 from the middle Pennsylvanian. 

 It has but two bones in the prox- 

 imal row, corresponding quite to 

 the astragalus and calcaneum of 

 mammals and the typical reptiles. 

 Beyond these, six, and only six, 

 bones are visible, five of which 

 are undoubted tarsalia; one may 

 be a centrale. The whole num- 

 ber, eight, was the most known 

 in any reptile until recently. 

 Nine bones are present in the 

 tarsus of Ophiacodon (Fig. 152), 

 from the uppermost Pennsyl- 

 vanian or basal Permian of New 

 Mexico: two in the proximal 

 row, the astragalus and cal- 

 caneum, two centralia in the 

 middle row on the tibial side; and five tarsaha in the distal row, 

 one corresponding to each metatarsal. Since this discovery two 

 centralia have also been found by Watson in the genus Broomia 

 (Fig. 137 d), from the Permian of South Africa; and probably 

 also two in the cotylosaurian genus Labidosaurus. The second 



Fig. 150. Geosaurus (Thalattosuchia). Elon~ 

 gate left hind leg, and paddle-like left front 

 leg. After Fraas. 



