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Rh reptiles there is no evidence of a lost prepollex. Theriodesmus (Fig. 138 ) of the same group, as restored by the author from Seeley's figures, also lacks the fifth carpale, though the intermedium is not small. The complete carpus is unknown in other members of the Therapsida.



. 139. Rhynchocephalian limbs: A, B, Sphenodon. After Howes and Swinnerton. About seven eighths natural size. C, Sauranodon. After Lortet. Nine eighths natural size. D, Pleurosaurus. After Lortet. Nine eighths natural size.

Sphenodon (Fig. 139 ) of the Rhynchocephalia is the only modern reptile which has retained the primitive structure and arrangement of the carpal bones. Extinct members of the order and its allies of the Diaptosauria are not sufficiently well known to determine whether this primitive structure is general, though doubtless it has been for the most part. In Rhynchosaurus, in a specimen figured by Newton, traces of the missing bones have been shown in dotted lines, indicating a primitive carpus save for the pisiform which was doubtless present.

The carpus of the Crocodilia has been strangely modified (Fig. 140 ). It is composed of four bones only in all forms so far as known: