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. 



(c) The mesencephalon contains no ventricular expansion, its 

 substance being perforated only by a narrow tube, the cere- 

 bral aqueduct uquaeductus cerebri), which connects the 

 third with the fourth ventricle. 



(d) 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 for a 

 short distance in the middle line to form the unpaired body of the 

 fornix (corpus fornicisi. 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. 



(e) 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. 



7. 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) 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. 



(b) 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. 



