1902.] Oslwni, Dolichocephaly a7id Brachycephaly in Mammals. 85 



no doubt be found by examination in every famih- of mam- 

 mals. 



But every exception has some special adaptive significance. 

 For example, the nasals in the Tapirs and the Proboscidea 

 are abbreviated not as an expression of brachj'cephaly but 

 in correlation with a prehensile upper lip or proboscis. The 

 mastoid portion of the periotic, generally exposed in dolicho- 

 cephalic types such as the Horses, persists also in the 

 brachycephalic Primates, for the insertion of one of the 

 most important muscles of the neck. The contrasts of 

 brachycephalic with dolichocephalic characters, brought out 

 in the above table, therefore are limited in the various mam- 

 malian families by special adaptive conditions. 



Significance of Dolichocephaly. 



The earliest known Ungulates have moderateh^ elongate 

 or mesaticephalic skulls, from which it follows that brachy- 

 cephaly and dolichocephaly are for the most part secondary. 



Fig. 4. Dolichocephalic skull of Baboon, Cynoccf>halus oliiuiceus. 



In Titanotheres and Rhinoceroses the}' are definitely pro- 

 gressive characters. The earliest horses (Protorohippus, 

 Hyracotheriiiin) are already specialized in the direction of 



