The Brahi 



?93 



The cerebral hemispheres are developed first as a median pro- 

 longation at the anterior end of the fore-brain, which later be- 

 comes divided into the two hemispheres by its anterior wall 

 growing back into it from the front. These two hemispheres 

 appear first as large vesicles with very thin walls and these cavi- 

 ties persist throughout life as the lateral ventricles of the brain 

 which communicate, through the foramina of Munro, with the 

 third ventricle. See Figs. 41 and 60. 



Fig. 31. Hydrocephal,us. Cai,f. (After photograph). 



In some cases the fluid in these cerebral hemi.spheres becomes 

 enormously increased, to constitute the fetal disea,se of hydro- 

 cephalus as indicated in Fig. 31. In other instances the cerebral 



