THE FIRST CEREBRAL VESICLE. 



69 



far the largest portion of the brain in higher vertebrates. The corpora striata 

 appear as thickenings of the floor of tho hemisphere vesicles, and outside them the 



Ma, 



Fig. 78. THREE SECTIONS THROUGH THE FORE-BRAIN OF A FOUR AND A HALF WEEKS EMBRYO. (His.) 



A. Through the lower anterior part of the fore-brain ; S, falx : Sf. fold of roof passing below falx 

 towards the third ventricle ; Bf, fold forming the sulcus ammonis ; v.JKl, h.RL, anterior and posterior 

 parts of olfactory lobe ; Cs, corpus striatum ; 0. IV, groove continuous with optic stalk ; P. s, pars 

 subthalarnica ; T.c, tuber cinereum. 



B. Section a little further back. Sf is replaced by a less prominent but broader fold of the roof, 

 Ad, which subsequently receives the choroidal . vessels, and is therefore the choroidal fold; Us, 

 hemisphere vesicle ; Th, thalamus ; S.M, sulcus of Monro, below and behind the thalamus. 



C. Still further back ; Ad, choroidal fold here projecting into lateral ventricles, but still free from 

 mesoblast and bloodvessels ; Ma, mammillary tubercle. The other lettering as before. 



