The Brain 



293 



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 verj- 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. Hydroceph.\lu.s. Calf, i After photograph). 



In some ca.ses the fluid in these cerebral hemispheres becomes 

 enormously increa.sed. to constitute the fetal disease of hj^dro- 

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



