THE NERVOUS SYSTEM 



217 



294. The Convolutions of the Cerebrum. The cerebrum 

 has a peculiar folded-up appearance, its various folds or 

 convolutions, as they are called being separated by deep 



FIG. 136. The Left Half of a Vertical Median Section of the Brain. 



A, frontal lobe of the cerebrum ; B, parietal lobe ; C, parieto-occipital lobe ; 

 D, occipital lobe ; E, cerebellum ; F, arbor vitae ; H, pons Varolii ; A", me- 

 dulla oblongata. 



clefts, sometimes nearly an inch deep. In this simple way 

 the surface of the brain is increased many fold. The cere- 

 brum is made up of both white and gray matter. 



The interior of the brain is made up chiefly of the 

 white nerve substance just spoken of, and also important 

 masses of gray matter called ganglia. The gray matter is 

 the outer layer, about one eighth of an inch in thickness, 

 and is spread over the white substance somewhat like a 

 silk handkerchief which has been crumpled up. 



