THE TELENCEPHALON. 



1161 



1007) appears triangular in outline. The upper side or base of the triangle, slightly 

 curved towards the ventricle, is the lower surface of the arched corpus callosum and 

 its antero-lateral radiations ; the mesial side is approximately vertical and formed 

 by the septum lucidum ; the lateral side bulges strongly towards the ventricle in 

 correspondence with the convexity of the massive head of the caudate nucleus. The 

 floor of this part of the ventricle is narrow, often a mere groove along the junction of 

 the sloping lateral and vertical mesial wall, and in front passes insensibly into the 

 concave anterior wall, formed by the lateral part of the hind surface of the genu of 

 the corpus callosum. 



The body (pars centralis) of the lateral ventricle includes that part of the space 

 which extends from the foramen of Monro to the bifurcation of the ventricle into its 



FIG. 1000. 



Corpus callosum 



Anterior horn of 

 lateral ventricle 



Caudate nucleus, head 

 Foramen of Monro 



Lenticula nucleus, 



sectioned 



Septum lucidum 



Cavity within septun 



^ - ' Fornix , anterior pillar 



1 Choroid plexus, 

 4 In body of 



Hippocampus 



Collateral eminence 



Fimbria 



Posterior pillar of 

 fimbria 



Collateral prorruber- 



ance in trigonum 



ventriculi 



Bulb of forceps 



posterior 



Calcar 



Posterior horn of 

 lateral ventricle 



Posterior horn 



of lateral ventricle 



Lateral ventricles seen from above after partial removal of corpus callosum and cerebral hemispheres. 



posterior and inferior horns, opposite the splenium of the corpus callosum. When 

 viewed in frontal sections (Fig. 1010), it appears as a narrow, obliquely horizontal 

 cleft, directed somewhat upward, roofed in by the corpus callosum. Its mesial 

 wall is formed in front by the hind part of the septum lucidum and behind the 

 latter by the fornix where it is attached to the under surface of the corpus callosum. 

 A distinct lateral wall is wanting, the ventricle being here closed by the meeting 

 of the floor and roof. Its floor is constituted by several structures of importance 

 which, named from without inward, are: (i) the caudate nucleus ; (2) an oblique 

 groove (sulcus intermedius), which extends from before backward and outward, 

 between the caudate nucleus and the thalamus, and lodges, in addition to the vein 

 of the corpus striatum, a white band of nerve-fibres known as the itznia 

 semicircularis ; (3) a narrow portion of the upper surface of the thalamus, which is 



