328 



MAMMALIA. 



Mesohippus (figs. 187, 188). Almost identical with Anchitherium, but 

 the incisors only slightly or not at all pitted. A rudiment of metacarpal v 

 occurs in the manus. The typical species, Mesohippus bairdi, with a skull 

 about O18m. in length, is kuown by nearly complete skeletons from the 

 Lower Miocene (White River Formation) of Dakota. There is a slight 

 trace of a fibular facette on the calcaueum (fig. 188, c/.). 



Mesohippus intermedius ; left hind foot, lateral (A) and anterior (B) aspects, and 

 right fore foot, anterior (c) and lateral (D) aspects, nearly one-third nat. 

 size. L. Miocene (White Eiver Formation) ; Dakota, c 2 , c 3 , middle and 

 external cuneiform ; cb., cuboid ; cf., facette on calcaneum for fibula ; en., 

 cuneiform ; lu., lunar ; m, magnum ; n, navicular ; p, pisiform ; sc., sca- 

 phoid; un., unciform. n v, number of digits. (After Osborn and Wortman.) 



The Palaeotheriidse pass almost insensibly both into the 

 rhinoceroses and the horses, and thus presumably left de- 

 scendants which are included in one or other of these com- 

 paratively recent families. Before the close of the Eocene 



