THE BRAIN. 



163 



The Brain (Fig. 66) is far larger than the spinal cord 

 and more complex in structure. It weighs on the average 

 about 1415 grams (50 ounces) in the adult male, and about 

 155 grams (5.5 ounces) less in the female. In its simpler 

 forms the vertebrate brain consists of three masses, each 

 with subsidiary parts, following one another in series from 

 before back, and known as the fore-brain, mid- brain, and 

 hind-brain respectively. In man the fore-brain, A, weighing 



FIG. 66. Diagram illustrating the general relationships of the parts of the 

 brain. A, fore-brain ; 6, mid-brain ; B, cerebellum ; C, pons Varolii ; D, me- 

 dulla oblongata ; B, C, and D together constitute the hind-brain. 



about 1245 grams (44 ounces), is much larger than all the 

 rest put together and laps over them behind. It consists 

 mainly of two huge convoluted masses, separated from one 

 another by a deep median fissure, and known as the cerebral 

 hemispheres. The immense proportionate size of these is 

 very characteristic of the human brain. Beneath each 

 cerebral hemisphere is an olfactory lobe, inconspicuous in 

 man but often larger than the cerebral hemispheres, as in 

 most fishes. Buried in the fore-brain on each side arc two 

 large gray masses, the corpora striata and optic tlialami. 

 The mid-brain forms a connecting isthmus between the 

 two other divisions and presents on its dorsal side four 



