CHAPTER lY. 



THE BRAIN. 



(Plate VI.) 



The brain of the Dinocerata is one of the most peculiar features of the 

 group. It is especially remarkable for its diminutive size. It w;is 

 proportionally smaller than in any other known mammal, recent or 

 fossil, and even less than in some reptiles. It was, indeed, the most 

 reptilian brain in any known mammal. In IHiiocrras mirahile (number 

 1036), the entire brain was actually so diminutive that it could apparently 

 have been drawn tlirough the neural canal of all the presacral vertebrae, 

 certainly through the cervicals and the lumbars. 



The size of the entire brain in Dimceras, as compared Avith that of the 

 cranium, is shown in the accompanying cuts, figures 7 and 8, page 15, and 

 figures 57 and 58, page 54. The size of the brain-cavity, and its position 

 in the skull in Tiiioceras, also, is represented in figure 9, page 16, and 

 figure 67, page 63. 



The most striking feature in the bi-ain-cavity itself, is the relatively 

 small size of the cerebral fossa, this being l)ut little larger than the 

 cerebellar portion. This is well shown in Plate VI, the figures of which 

 are drawn froln the cast of the bi-ain-cavity of Diitoccras mirahUe, the type 

 of the genus. ~' 



