THE NERVOUS SYSTEM 



381 



gence, being very complex in the elephant and whale, 

 monkey and man. As a rule, they are proportioned to 

 the intelligence of the animal; yet the brains of the 

 dog and horse are smoother than those of the sheep 

 and donkey. Evi- 

 dently the quality of 

 the gray matter must 

 be taken into account. 

 Save in the bony 

 fishes, the cerebrum 

 is the largest portion 

 of the brain ; in man 

 it is over eight times 

 heavier than the cere- 

 bellum. 



The cerebellum, or 

 "little brain," lies be- 

 hind the cerebrum, 

 and, like it, presents 

 an external gray layer, 

 with a white interior. 

 In mammals, it is like- 

 wise finely convoluted, 

 consisting of gray and 

 white laminae, and is 

 divided into two lobes, 

 or hemispheres. In 

 the rest of the verte- 

 brates, the cerebellum 

 is nearly or quite 

 smooth ; and in the lowest fishes it is merely a thin 

 plate of nervous matter. In many vertebrates, how- 

 ever, it is larger compared with the cerebrum, than 

 in man, since in man the cerebrum is extraordinarily 

 developed. 



FIG. 335. Brain of the Horse upper view, one 

 fourth natural size ; a, medulla oblongata ; 

 b, lateral and middle lobes of cerebellum; c, inter- 

 lobular fissure ; d, cerebral hemispheres; e, olfac- 

 tory lobes. 



