THE FOEM-EELATIONS OF THE HUMAN BEAIN. 187 



You observe there that, arising from the apex of the temporal lobe, it arches 

 over the interbrain in a curve and descends in front of this to the boundary 

 between the forebrain and interbrain. 



After the fornix, and the plexus chorioideus attached to it, is divided 

 and cut away, a view of the opened ventricles is obtained (Fig. 125). The 

 unpaired ventricle lying in the median line is the cavity of the primary fore- 

 brain, now called the ventriculus tertms. At its anterior end the fornix 

 ascends from below. Then, on each side of the fornix there is found a com- 

 munication of the ventriculus medius with the ventriculi laterales: the 

 foramen Monroi. The part of this ventricle which lies in the frontal lobe 

 is called the anterior horn, the part in the occipital lobe the posterior horn, 

 and that in the temporal lobe the inferior horn. A finger could easily be 

 introduced into each of the horns. The basal regions of both hemi- 

 spheres are connected with one another by means of the commissura 



Stflk HO Vordeftidn 

 imd Zwiidtathm 



Fig. 126. — Inner aspect of the embryonic hemisphere shown in Fig. 23. 

 Shows the inner lower border of the hemisphere, which becomes thickened into 

 the white medullary line of the fornix. The latter, however, only becomes 

 meduUated after birth. Zwisohenhiru, Interbrain. Torderhirn, forebrain. 

 Stelle, etc.. Point where the forebrain and interbrain meet. 



anterior. The bundles of white, medullated fibers composing it are seen 

 passing across in front of the pillars of the fornix. 



The nucleus caudatus rises from the floor of the lateral ventricle. Far- 

 ther posteriorly parts become visible which no longer belong to the hemi- 

 spheres: the interbrain {thalamus opticus) and the midbrain {corpora quadri- 

 gemina). Behind these is seen the roof of the hindbrain (the cerebellum). 



The cavity between both thalami, the ventriculus medius, was at one 

 time the cavity of the interbrain-vesicle. It is closed in above by the plicated 

 plexus chorioideus, at the posterior end of which lies the conical projection, 

 the corpus pineale, now become solid. The floor of the interbrain, which is 

 naturally formed in front by the embryonic terminal lamina, consists of gray 

 matter descending like a funnel toward the base of the brain. This pro- 



