DISSECTING MANUAL. 



Olfactory Lobe. This comprises a posterior lobule (locus 

 perforates anticus) , a small triangular gray area in front of the 

 optic tract; and an anterior lobule composed of the trigonum 

 olfactorium, area of Broca, and olfactory bulb, tract, and 

 roots. The olfactory tract is a narrow white band which ex- 

 pands anteriorly (olfactory bulb) and lies in the olfactory 

 sulcus; posteriorly it divides in two diverging roots which en- 

 close a small triangular gray area (trigonum olfactorium). 

 The mesial root curves inward behind a small area (area of 

 Broca) to the callosal gyrus; the lateral root runs backward 

 and outward over the locus perforatus anticus and disappears; 

 a few fibres (the occasional middle root) may arise from the 

 tract posteriorly and enter the trigonum. [569] 



Corpus Callosum. This is an arched commissure, convex 

 above and concave below, which unites the inner surfaces of 

 the hemispheres for nearly half their length and lies nearest 

 their anterior extremities. In the hemispheres its fibres di- 

 verge widely (radiatio corporis callosi), those from the body 

 and upper part of the splenium forming a definite layer(tape- 

 tum), and those from the rest of the splenium running back- 

 ward in a bundle (forceps major). Its thick posterior end 

 (splenium) is tightly folded on itself below. Its thinner an- 

 terior end (genii) also bends on itself ; the lower part (rostrum) is 

 separated from the upper by an interval, thins out rapidly and 

 joins the lamina cinerea. The body is still thinner. [570] 



The upper surface is covered by a thin cortical gray layer; 

 it presents a mesial furrow between two delicate bands (stria 

 longitudinalis medialis), and a similar band (stria longitudi- 

 nalis lateralis) on each side. Posteriorly the strise and gray 

 matter join the gyrus dentatus; anteriorly the mesial striae 

 diverge, as gyri geniculi, and are connected, through the cor- 

 tex, with the locus perforatus anticus. The under surface is 

 attached mesially to the fornix and septum lucidum; else- 

 where it is mostly free, covered by ependyma, and roofs over 

 the lateral ventricles. [571] 



[42] 



