The: Ce;ntral Ni^rvous System. 193 



bral aqueduct (aquaeductus 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 tcrminalis. 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 fornicis). They begin in the mammillary body, and 

 passing vipward 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 pelluci- 

 dum, 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 carefully away until the 

 white surface of the corpus callosum is well exposed. Bv 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. 



(c) The floor is formed by a greatly thickened mass of nervous 

 matter, appearing from the interior of the ventricle in the 

 form of two convex ridges. One of these, posterior and 

 medial in position, is the hippocampus. The other is 

 smaller, anterior and lateral in position, and is the corpus 

 striatum. Between the two bodies the pigmented vascular 

 tissue of the chorioid plexus of the lateral ventricle may be 

 made out. 



(d) On the medial wall, the thickened posterior portion forms 

 the body of the fornix, immediately in front of which is the 

 thinner portion of the wall, described above as the septum 

 pellucidum. 



8. The passage of the olfactory nerves to the ethmoturbinal surfaces 

 may be traced by removing the nasal bones and working downward 

 toward the cribriform plate, or the remaining portion of the skull con- 

 taining the nasal region still intact may be divided vertically for a more 

 extended examination of the nasal fossae. The features to be observed 

 are largely those described in connection with the skeleton (pp. S3, 92). 



