GENERAL CONFORMATION AND HISTOLOGY OF BRAIN. 



35 



of the arch (crura fornicis), and, posteriorly, the descending 

 portion, a white line of medullary matter, which, passing along 

 the border of the hemisphere, bounds the temporal lobe on its 

 inner aspect. If you connect the points F.I mid. F.II, in Fig. 19, 

 with a gentle curve which passes over the optic thalamus. you 

 wiH have restored the course of the fornix. In the accompany- 

 ing median section of an embryonic brain you can easily dis- 

 tinguish the course of the fornix. In our dissection (Fig. 19) 

 you can see the thalamus behind the nucleus caudatus. It 

 belongs to the inter-brain, and has developed from its lateral 

 walls. The space between the 

 two thalami is the cavity of the 

 former inter-brain vesicle. Of 

 its roof onlv a thin lavcr re- 







mains, the most important part 

 of which is the pineal gland. 

 Fig. 4 shows how this arose by 

 a process of protrusion. All 

 the rest of the roof of the former 

 vesicle is only present in the 

 form of a thin epithelium, be- 



Irmo'in 

 U M 



which cover the middle ventricle. 



The floor of the inter-brain, 



which is, of course, formed an- 



teriorly of the embryonic terminal lamina, consists of a mass of 



gray matter, which is prolonged in a funnel-shaped manner 



toward the base of the skull. This projection is called the tuber 



cinercMim. and its cavity the infimdibulum. It is not shown in 



/ 



Fig. 19. but can be clearly seen in the median section (Fig. 17). 

 At its extreme end the tuber cinereum is fused into the fold 

 of pharyngeal mucous membrane which grows toward it, as 

 shown in Fig. 4. At a later stage the latter is cut off from the 

 pharynx and remains in the cavity of the skull, whore, in con- 

 nection with the tuber cinereum, it forms the hypophysis, an 



wo Vordcrhirn 

 Tjvischenhirn. 



FIG. 20. 



Inner aspect, of the embryonic hemi- 

 sphere, shown in Fig. 7. Shows the inner 

 lower border of the hemisphere, which be- 



to a nlpims of vessels conies thickened into the white medullary 



line of the fornix. The latter, however, only 

 becomes medullary after birth. 



S/'Ue wo Vorderliirn um! Zirixrlx-nliirn ziismn- 

 menslosaen, Point where the fore-brain and mid-brain 

 meet. 



