THE NERVOUS SYSTEM. 



173 



them the small cerebral hemispheres, then the large optic 

 lobes (in which originate the nerves of sight), and, last of 

 all, the cerebellum. Not till we reach Man and the Apes 

 do we find the cerebrum so highly developed as to overlap 

 both the olfactory lobes in front and the cerebellum behind. 



Functions of the Brain. — The cerebrum is the seat of in- 

 telligence and will. It has no direct communication with 

 the outside w r orld, receiving its consciousness of external 

 objects and events through the spinal cord and the nerves 

 of special sense. 86 



The cerebellum seems to preside over the co-ordination 

 of the muscular movements. When removed, the animal 



Fto. 141. — A, C, tipper and side views of the Brain of a Lizard ,• B, D, upper and side 

 views of the Brain of a Turkey: Olf, olfactory lobes ; Hmp, cerebral hemispheres ; 

 Pn, pineal gland ; Mb, optic lobes of the middle brain ; Cb, cerebellum ; MO, me- 

 dulla oblongata; ii, optic nerves; iv and vi, nerves for the muscles of the eye; 

 Py, pituitary body. 



desires to execute the mandates of the will, but cannot ; 

 its motions are irregular, and it acts as if intoxicated. It 

 is usually largest in animals capable of the most compli- 

 cated movements ; being larger in the Ape than in the 

 Lion, in the Lion than in the Ox, in Birds than in Eep- 

 tiles. The cerebellum of the Frog is, however, smaller 

 than that of Fishes (Figs. 139, 140). The olfactory and op- 

 tic lobes receive the messages from their respective nerves. 



