756 



THE NERVOUS SYSTEM. 



losd), produced by the escape of blood from divided blood-vessels. In inflammation 

 or great congestion of the brain these are very numerous and of a dark color. If 

 the remaining portion of one hemisphere is slightly separated from the other, a 

 broad band of white substance will be observed connecting them at the bottom of 

 the longitudinal fissure ; this is the corpus callosum. The margins of the hemi- 

 spheres which overlap this portion of the brain are called the labia cerebri. Each 

 labium is part of the convolution of the corpus callosum (gyrns fornicatus), and 

 the space between it and the upper surface of the corpus callosum has been termed 

 the ventricle of the corpus callosum (Fig. 446). 



The hemispheres should now be sliced off to a level with the corpus callosum, 

 when the white substance of that structure will be seen connecting the tAvo 

 hemispheres. The large expanse of medullary matter now exposed, surrounded 

 by the convoluted margin of gray substance, is called the centrum ovale majus of 

 Vieussens. 



The corpus callosum (Figs. 442, 446) is a thick stratum of transverse fibres 

 exposed at the bottom of the longitudinal fissure. It connects the two herni- 



Sept luc. Corp caU 



Mid. com 



Pin. gland 



Lam. quadrig. 



Splenium 

 Aq. Sylv. 



Hipp. 



gyms 



Opt. ch/ ^ body I Pons\ 



FIG. 446. Antero-posterior median section of the brain, X . (Henle.) 



spheres of the brain, forming their great transverse commissure, and forms the 

 roof of the lateral ventricles. It is about four inches in length, extending to 

 within an inch and a half of the anterior, and to within two inches and a half 

 of the posterior, end of the hemispheres. It is somewhat broader behind than in 

 front, and is thicker at either end than in its central part, being thickest behind. 

 It presents a somewhat arched form (Fig. 446) from before backward, and termi- 

 nates anteriorly by curving downward and backward between the frontal lobes. 

 This distinct bend is named the genu, whence it is still continued downward and 

 backward to the base of the brain, where it blends with the lamina cinerea. The 

 reflected portion of the corpus callosum is called the beak or rostrum : it becomes 

 gradually narrower as it passes backward, and is attached by its lateral margins 

 to the frontal lobes. At its termination, besides blending with the lamina cinerea, 

 the corpus callosum gives off two small bundles of white substance, which, diverg- 

 ing from one another, pass backward, across the corresponding anterior perforated 

 space, to the entrance of the fissure of Sylvius, to enter the end of the temporal 



