CORPUS CALLOSUM. 



521 



hemispheres, which overlap this portion of the brain, are called the Mia cerebri. 

 Each labium is part of the convolution of the corpus callosum (gyrus fornicatus), 

 already described ; and the space between it and the upper surface of the corpus 

 callosum has been termed the ventricle, of the corpus callosum. 



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 together both 

 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 is a thick stratum of transverse fibres, exposed at the 

 bottom of the longitudinal fissure. It connects the two hemispheres of the brain, 

 forming their great transverse commissure ; and forms the roof of a space in the 



Fig. 266. Section of the Brain. Made on a level with the Corpus Callosum. 



interior of each hemisphere, the lateral ventricle. 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, part of the brain. 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, from before backwards, 

 terminating anteriorly in a rounded border, which curves downwards and back- 

 wards, between the anterior Jobes to the base of the brain. In its course, it forma 

 a distinct bend, named the knee or genu, and the reflected portion, named the 

 beak or rostrum, becoming gradually narrower, is attached to the anterior cerebral 

 lobe, and is connected, through the lamina cinerea, with the optic commissure. 

 The reflected portion of th,e corpus callosum gives off, near its termination, two 



