mi I ill 



\\ i jitiniiit: nf t ! .' mid I-: 



ptence of the \ the 



neural tube, oooupiee tin- i -iii<n ami pi. 



prominence of tin- head (_lig. 158 a), it is afterwards OOVered in from 

 above l>y the other part- of the brain, which .-: more 



voluminous, I ho cerebellum and e ivhrinn. 

 to tin- IMSI' of tin- ln-aiii (eompai ' ///// will; 



(4) .!/- -is of the Second or Betwt Vesicle. 



The btt ncfe also remains -mall. Inn undergoes a 



(t intending changes, since, apart from the optic vesicles, 



which grow out from its walls, two other gee, of proble- 



matical meaning, lure develop, d from it the pineal ^land and the 



hypophysis. 



In the case of the between-brain vcsid . it is only in the. la- 

 walls that a cons-ideraM*- aiuount uf nT\r->nltancc is formed. I'.. 

 this means the walls thicken into the optic thalumi with tln-ir 



1 ionic layers. Between them the cavity of the vesicle is ict. 

 as a narrow vertical li.-sun-, known as the third i-i-ntricle; it is 

 united with the fossa rhomhoidalis l>y means of the aqueduct of 

 SYLVIUS. The floor remains thin and at an early period becomes 

 mated downwards; it thus acquires the form (figs. 235, 241 tr) 

 <-f a short funnel "////), with the apex of which is united 



the hypuphyMs, soon to b;- fully d. scribed. 



The roof presents in its metamorphosis a striking similarity to the 

 corresponding part of the after -brain vesicle (fig. 241). It persists 

 as a simple, thin epithelial layer, unites with the very va.-cular 

 pia mater, which sends out in this case also villous outgrowths 

 with capillary loops which pass into the third ventricle, and together 

 with it coi;>titutes the anterior choroid plexus (tela chor< 

 or superior). When in withdrawing the pia mater the choroid 

 plexus is also removed, the third ventricle is opened : thu> i> {rod need 

 the anterior great fissure of the brain through which, as thn 

 the structure of the same name in the medulla Q 

 penetrate into the cavitie- of the brain. 



The agreement with the medulla oblongata i> e.\preed in still 

 another point. As in th case of the latter the edges of the roof- 

 plate develop into thin medullary bard-, by in. ans of which the 

 attachment to the sides of the fossa rhcmbjidalis is accomplished, so 



