Marsh Collection, Peabody Museum. 



351 



109 



The tibia, figure 109, is the most characteristic part of the 

 skeleton preserved, and in the absence of the feet this bone, 

 especially in its distal end, may be said to be one of the 

 most distinctive of the entire Primate 

 skeleton. The chief characteristics 

 of the tibia in the lemurs and mon- 

 keys may be briefly stated as follows : 

 The proximal surface is divided into 

 two subequal articular facets, which 

 are separated by a relatively high, 

 pointed tibial spine. The long, 

 straight shaft is much compressed 

 from side to side and marked at the 

 lower part of it& upper third in front 

 by a roughened tubercle for the attach- 

 ment of the semitendinosus, one of 

 the chief inner hamstring muscles. 

 The distal extremity is relatively nar- 

 row transversely and limited internally 

 by a large pointed malleolus. The 

 articular surface which it offers to the 

 astragalus is slightly concave from 

 before backward, but in a transverse 

 direction is almost plane and slopes 

 outward toward the fibula. This 

 arrangement is associated with a highly 

 characteristic form of the astragalus, 

 which in turn is indicative of a pre- 

 hensile pes. Among the Rodentia, 

 on the other hand, the tibia and astrag- 

 alus are equally characteristic and 

 distinctive of another type of foot. 

 In the fossil under consideration, the 

 tibia has every mark and feature of 

 the Primate so unmistakably stamped upon it that I have no 

 hesitancy in referring the species to this order, in a position not 

 far removed from CTieiromys. 



Discussion. — We have ah-eady seen that in dieiroiiiys we 

 have an undisputed Primate, in which the incisors have under- 

 gone modification exactly similar to that of the Podentia. We 

 have further seen that the presence of these teeth in this animal 

 is associated not only with a peculiar modification of the third 

 finger of the hand, but with a grub-eating habit and a tendency 

 to degeneration of the molars and premolars. JS'ow in the 

 extinct creature before us, we have, if the evidence derived 

 from its osteology can be trusted, an equally unmistakable 

 Primate undergoing the same modification of the incisors, and 



Figure 109. — Right tibia 

 of Metacheiromys Marshi 

 Wortman ; front and end 

 views; natural size. (Type.) 



