194 



THE OSTEOLOGY OF THE REPTH^ES 



There are valid reasons for doubting the reappearance of the inter- 

 medium after its loss in the terrestrial ancestors of the plesiosaurs. 

 It may be the enlarged centrale. The bones in the distal row may be 

 the first, fused second and third, and the fourth tarsalia. The homol- 

 ogies of the mesopodial bones of the Ichthyosauria (Fig. 158 c, d), 

 where a like similarity between the front and hind limbs exists, are 



Fig. 159. Paddles of Plesiosaurs: A, right hind paddle of Thaumatosaurus, a.ktT Fraas. 

 B, right hind paddle of Trinacromerum. C, right front paddle of same individual. /, 

 femur; fb, fibula; /, tibia; h, humerus; r, radius; «, ulna. 



even more doubtful. There is the same objection to the recognition 

 of an intermedium tarsi in this order as in the plesiosaurs, whatever 

 may be the corresponding bone in the carpus. 



