84 Bulletin American Museum of Natural History. [Vol. XVI, 



Unequal Elongation of Face and Cranium. 



When we compare a long-skulled with a short-skulled 

 Rhinoceros the skull of the latter appears compressed antero- 

 posteriorly, as if composed of india-rubber, all the parts being 

 affected alike (Fig. 3). But although both the face and the 

 cranium in the Rhinoceroses and Horses appear to be affected, 

 this is by no means a general principle. In the Titanotheres 

 the face is shortened and the cranium greatly elongated, so 



Fig. 3. Influence of progressive brachycephaly upon the ear region of Perissodactyla. 

 A^ Dolichocephalic, Equus cabalhts. j9, Mesaticephalic, Tafiirus. C, Dolichocephalic, 

 Cerntof/iiniis sumairensis. D, Brachycephalic, Rhinoceros sondaicus. Disappearance of 

 mastoid portion of periotic, tn. P. Per, and enclosure of auditory meatus, e, a. m., inferiorly. 



that the distance between the orbit and the external auditory 

 meatus is very great, the molar teeth extending back beneath 

 the orbit. In the Horses, on the other hand, the face is greatly 

 elongated and the cranium only moderately so, and this is 

 true of by far the greater number of long-skulled Ungulates. 

 Such unequal elongation of different regions of the skull will 



