(c) 
(d) 
(e) 
We 
THE CENTRAL NERVOUS SYSTEM. 281 
commissure (commissura anterior). The ventral portion 
of the ventricle is projected toward the optic chiasma 
forming the recessus opticus, and into the infundibulum, 
forming the recessus infundibuli. 
The mesencephalon contains no ventricular expansion, its 
substance being perforated only by a narrow tube, the cere- 
bral aqueduct (aquaeductus cerebri), which connects the 
third with the fourth ventricle. 
The corpus callosum is shown in section. Anteriorly it 
appears to end in a somewhat club-shaped expansion, but in 
reality is extended as a thin sheet of fibres downward toward 
the lamina terminalis. Posteriorly it bends downward, 
forming the splenium, the latter being attached to the 
body of the fornix, which lies below it. 
The fornix consists of a pair of longitudinal fibre bands, fused fora 
short distance in the middle line to form the unpaired body of the 
fornix (corpus fornicis). They begin in the mamillary body, and 
passing upward as the columns of the fornix (columnae fornicis), meet 
in the body of the fornix, and afterwards diverge laterad as the pillars 
of the fornix (crura fornicis), ending in the hippocampus. 
Between the body of the fornix and the anterior portion of 
the corpus callosum is a thin area of the wall, the septum 
pellucidum, the lateral ventricles lying close together in 
this region. 
The nervous matter covering the corpus callosum may be 
removed from one hemisphere by first marking out a triangular 
area on the dorsolateral surface; then scraping the material care- 
fully away until the white surface of the corpus callosum is well 
exposed. By removing the corpus callosum the interior of the 
hemisphere may be examined. 
(a) 
(b) 
The lateral ventricle (ventriculus lateralis) is the extensive 
space enclosed by the hemisphere. It extends forward 
into the olfactory bulb and backward into the posterior free 
end of the hemisphere, passing a considerable distance 
behind the opening of the interventricular foramen. 
The excised portion of the hemisphere, forming the moder- 
ately thick roof and dorsolateral wall, consists largely of the 
peripheral grey cortex described as the pallium, 
