266 



THE HUMAN MECHANISM 



2. The brain of the mammal is built on the same funda- 

 mental plan as that of the frog, and differs from it mainly 

 in the greater number of neurones and in the complexity 



B 



FIG. 107. The base of the human brain, showing the cranial nerves 



A, the cms cerebri, composed largely of nerve fibers which connect the hind- 

 brain with the 'tweenbrain and forebrain ; B, the pans Varolii, the anterior floor 

 of the fourth ventricle, connected laterally with the cerebellum; (7, the bulb; 

 D, the cerebellum; E, the spinal cord 



of their connections with one another. This results in 

 great thickening of the ventricular walls and the formation 

 of a very complicated anatomical structure. Mammals are 

 especially characterized by an enormous development of the 



