362 



MAMMALIA. 



Dinocerata (p. 296). The typical and only satisfactorily known 

 genus is 



Protoceras (fig. 206). The skull is long and narrow, with the facial 

 region much produced and somewhat bent downwards from the cranial 

 region. The brain-case is large, and an impression of its cavity shows the 

 cerebral hemispheres of the brain to have been much convoluted. The 

 orbits are large and completely surrounded by bone. The premaxillse are 

 small and edentulous, and the narial opening is very large ; the nasal 

 bones are short, and so disposed that it seems probable that the animal 

 had a long flexible nose, if not a true proboscis. The maxillae are the 



FIG. 206. 



Protoceras celer ; skull and mandible of male, left lateral aspect, one-half nat. 

 size. L. Miocene (White Eiver Formation) ; Dakota. (After Marsh.) 



largest bones in the skull ; those of the male bearing the large canine 

 tusks at the anterior end, and raised above into a pair of rounded bosses, 

 which may have been horn-cores or tipped with callosities. The frontals 

 in the male (fig. 206) bear another diminutive pair of bony bosses ; while 

 the comparatively small parietals are surmounted by a third pair of 

 prominences which are much elevated. In the female skull, only the 

 parietal prominences occur, and these are quite small. The tympanic 

 bone is scarcely inflated. The mandible is long and slender. Apart from 

 the loss of the upper incisors, the dentition is complete ; and it is similar 

 to that of the Tragulidse. In the fore limb, the radius and ulna are 

 complete, but they tend to fuse together distally ; metacarpals in and iv 



