1132 



HUMAN ANATOMY. 



The posterior wall of the third ventricle is very short and includes the base of 

 the pineal body, with the opening into the minute pineal recess, the posterior com- 

 missure and the orifice leading into the Sylvian aqueduct. The floor slopes rapidly 

 downward and forward (Fig. 976) and comprises a small part of the tegmentum 

 of the cerebral peduncles, the posterior perforated substance, the mammillary bodies, 

 and the tuber cinereum with the infundibulum structures already described and 

 included within the interpeduncular area on the base of the brain. Corresponding 

 with the position of the superficial elevation, the ventricle exhibits the diverticulum 

 of the infundibulum. The optic chiasm marks the anterior limit of the floor and the 

 beginning of the anterior wall. Immediately above the chiasm the anterior wall 

 exhibits a diverticulum, the optic recess, from which the lamina cinerea ascends to 

 join the rostrum of the corpus callosum, in its course passing close to and in front 

 of the anterior commissure. The latter structure shows on the front wall of the 



FIG. 979. 



Cavity in septum lucidum 



Corpus callosum, cut 



Caudate nucleus 



Internal capsule 



Putamen of 

 lenticular nucleus 



Cut anterior end 

 of fornix 



Anterior pillars 

 of fornix 



Anterior commissure 



Lateral ventricle 



Ependyma covering 

 ta.-nia semicircularis 

 and vena terminalis 



Lamina cinerea, above__- ' Thalamus. anterior tubercle 



\ X Foramen of Monro 



Optic chiasm Lamina cinerea 



Portion of frontal section of brain passing through foramina of Monro, showing anterior wall of third ventricle 

 modelled by anterior commissure and pillars of fornix. 



ventricle as a transverse ridge between the descending and slightly diverging anterior 

 pillars of the fornix (Fig. 979). Although distinctly modelling the ventricular 

 walls, all of these bands are excluded from the ventricle by its ependymal lining. 



THE TELENCEPHALON. 



The telencephalon, or end-brain, consists of two fundamental parts, the hemi- 

 sphaerium and the pars optica hypothalami. The latter includes: (i) the 

 lamina cinerea (terminalis}, (2) the optic commissure, (3) the tuber cinereum and 

 (4) the pituitary body, all of which have been already considered, as a matter of con- 

 venience, in connection with the diencephalon and the third ventricle. The hemi- 

 sphere comprises: (i) the pallium, (2) the rhinniccphalon, and (3) the corpus 

 strnition. The first of these subdivisions undergoes such enormous development in 

 the anthropoid apes and in man, that the pallium' becomes the dominating factor and, 

 expanding upward, laterally and backward as the great cerebral mantle, not only 

 forms the chief bulk of the cerebrum, but overlies the derivatives of the other brain- 

 segments to such an extent that these parts are to a large measure covered and 

 deposed from their primary position on the free dorsal surface of the brain. In conse- 

 quence in man, in whom the pallium reaches its highest development, the thalami, 

 corpora quadrigemina and the cerebellum are masked by the hemispheres and occupy 

 topographically a dependent position. The rkivencephalon, on the contrary, is in 

 man only feebly developed and rudimentary in comparison with the conspicuous and 

 bulky corresponding structures possessed by animals in which the sense of smell is 

 highly developed. The corpus striatum, consisting of two large masses of gray 



