INTERIOR SURFACE OF THE FORE-BRAIN. 107 



fibers four and a half inches broad, from before backward, which 

 joins the hemispheres together. It constitutes the great com- 

 missure, being composed chiefly of those medullated cortical 

 axones which end in arborizations about cortical cells of the 

 opposite hemisphere. It contains some fibers which belong to 

 the internal capsule; and, also, collaterals from capsular and 

 association fibers. The corpus callosum is placed nearer to the 

 anterior than the posterior pole of the hemispheres. Separating 

 the hemispheres above, it is seen in the bottom of the longitudinal 

 fissure. It is about an inch in transverse length. 



The upper surface is concave from side to side, and divided 

 in the median line by a longitudinal raphe (Figs. 30 and 34). 

 Transverse striae are plainly visible. Two longitudinal striae 

 are also found running on either side of the raphe; one next the 

 raphe, the medial longitudinal stria; and the other near the lateral 

 end of the callosum, the lateral longitudinal stria. The medial 

 and lateral longitudinal striae are imbedded in a thin sheet of gray 

 substance spread over the corpus callosum; altogether they con- 

 stitute the gyrus supracallosus. If traced around the posterior 

 border of the callosum, this supracallosal gyrus is found to be 

 continuous with the fasciola cinerea and, through that, with the 

 fascia dentata. The gyrus supracallosus becomes the gyrus sub- 

 callosus (peduncle of corpus callosum) after it winds around the 

 anterior border of the corpus callosum. As such it is continued 

 downward between the lamina terminalis and the posterior parol- 

 factory sulcus to the base of the cerebrum, and then across the 

 anterior perforated substance to the uncus. At the anterior and 

 at the posterior border, the corpus callosum is bent downward 

 (scroll-like); hence, it is superiorly convex from before back- 

 ward. 



Its inferior surface (Figs. 29 and 30) is concave antero-poste- 

 riorly and near its posterior border is fused with the body of the 

 fornix. Anterior to that fusion, it is joined to the fomix, along 

 the median line, by the septum pellucidum. 



The posterior border (Fig. 29) is flexed downward from the 

 horizontal about forty-five degress. Giving passage to the fibers 

 which join the middle and posterior parts of the hemispheres, 



