144 



EMBRYOLOGY. 



(figs. 254 2*1 and 255 agf}. Instead of thickening and developing 



nerve-substance, it becomes 

 attenuated, and is trans- 

 formed into a single layer 

 of flat epithelial cells, which 

 are firmly united with the 

 pia mater. The latter then 

 becomes very vascular along 



Fig. 253. Lateral view of the brain of an embryo Calf 11 , r i i i 



the entire fold, and grows 

 into the lateral ventricle in 

 the form of tufts, which 

 carry the epithelium before 

 them. In this way the 

 lateral choroid plexus arises 

 (fig. 254 pi], which afterwards, in the adult, fills a part of the cella 

 media and in- 

 ferior cornu. 

 It begins at 

 the foramen of 

 M o N R o (fi g. 



cst 



5 cm, long. The lateral wall of the hemisphere 

 has been removed. After MIHALKOVICS. Magni- 

 fied 3 diameters. 



cst, Corpus striatum ; ML, foramen of MONJIO ; agf, 

 plexus choroideus lateralis ; amf, hippucampal 

 fold; lit, cerebellum; Dp, roof of the fourth 

 ventricle; bb, pontal flexure ; mo, medulla ob- 

 longata ; mh, mid-brain (parietal flexure). 



it is continuous 

 with the an- 

 terior unpaired 

 choroid plexus 

 which has 

 arisen in the 

 roof of the be- 

 tween-brain 

 vesicle. If the 

 delicate vas- 

 cular pia mater 

 is drawn out 

 from the cho- 

 roid fissure, the 

 wall of the 

 brain, which is 

 reduced to a 

 thin epithe- 

 lium, is at the 

 median wall of 



a 



:;-/;*> 



i ip\\ r A 



.- \lf \ 



p *u \ c]l o 



Fig. 254. Transverse section through the brain of an embryo Sheep 



2 -7 cm. in length, after KOLLIKER. 



The section passes through the region of the foramen of MONRO. 

 st, Corpus striatum; m, foramen of MONRO; t, third ventricle; pi, 



plexus choroideus of the lateral ventricle ;/, falx cevebri ; th, deepest 



anterior part of the optic thalamns ; ch, chiasma ; o, optic nerve ; 



c, fibres of the crus cerebri ; /<, hippocampal fold ; p, pharynx; 



sa, presphenoid ; , orbito-sphenoid ; s, part of the roof of the 



brain at the junction of the roof of the third ventricle with the 



lamina terminalis ; I, lateral ventricle. 



same time destroyed, and there is produced in the 

 the hemisphere a gaping fissure, which extends from 



