NEEVOUS SYSTEM. 



639 



and farther over the medulla oblongata. The subsequent history 

 of the development of the encephalon is little more than a con- 



Fig. 239. 



FOETAL Pia, one and a quarter inch. 

 long. 1. Hemispheres. 2. Tubercuia 

 qnadrigemina. 3. Cerebellum. 4. Me- 

 dulla oblongaca. 



HEAD OF FCETAL PIG, three and a 

 half inches long. 1. Hemispheres. 3. 

 CereOellurn. 4. Medul'a ol-longata. 



tinuation of the same process ; the relative dimensions of the parts 

 constantly changing, so that the hemispheres become, in the adult 

 condition (Fig. 2-iO), the largest of all the divisions of the ence- 



Fig. 240. 



BRAI.V OP ADULT PIG. 1. Hemispheres. 3. Cerebellum. 4. Meduna oblougata. 



phalon, while the cerebellum is next in size, and covers entirely 

 the upper portion of the medulla oblongata. The surfaces, also, of 

 the hemispheres and cerebellum, which were at first smooth, become 

 afterward convoluted; increasing, in this way, still farther the 

 extent of their nervous matter. In the human foetus, these con- 

 volutions begin to appear about the beginning of the fifth month 

 (Longet), and grow constantly deeper and more abundant during 

 the remainder of foetal life. 



The lateral portions of the brain growing at the same time more 

 rapidly than that which is situated on the median line, they soon 

 project on each side outward and upward and. by folding over 



