230 



COMPARATIVE ANATOMY 



parts shows a kind of relief of certain underlying portions of the 

 brain. In some cases, only the larger divisions of the brain 

 (cerebrum and cerebellum) are thus indicated externally : in others, 

 a relief of the convolutions is also seen, and in Mustela and Lutra, for 

 example, it is almost complete on the lateral portions of the skull 



FIG. 175. CASTS OF THE BRAINS OF VARIOUS EOCENE MAMMALS. 

 (After Marsh.) 



Skull, with brain indicated, of A, Tillotherium f odium ; J3, Brontotherium ingens ; 

 C, Coryphodon hamatua ; and D, Dinoceras mirabile. E and F, ventral and 

 lateral views of the brain of Dinocera* mirabile. 



covered by the temporal muscles, and may even extend dorsally 

 to the middle line. 



II. PERIPHERAL NERVOUS SYSTEM. 



Two principal groups of peripheral nerves may be distinguished, 

 viz., spinal and cerebral, that is, those which arise from the 

 spinal cord and brain respectively: between them is an inter- 



