THE FORE-BRAIN OR PROSENCEPHALON 



829 



: 



the splenium shows that the posterior end of the corpus callosum is acutely bent 

 forward, the upper and lower parts being applied to each other. 



The superior surface is convex from before backward, and is about 2.5 cm. wide. 

 Its medial part forms the bottom of the longitudinal fissure, and is in contact 

 posteriorly with the low r er border of the falx cerebri. Laterally it is overlapped by 

 the cingulate gyms, but is separated from it by the slit-like callosal fissure. It is 

 traversed by numerous transverse ridges and furrows, and is covered by a thin 

 layer of gray matter, the supracallosal gyms, which exhibits on either side of the 

 middle line the medial and lateral longitudinal striae, already described (page 827). 



The inferior surface is concave, and forms on either side of the middle line the 

 roof of the lateral ventricle. Medially, this surface is attached in front to the 

 septum pellucidum; behind this it is fused with the upper surface of the body 

 of the fornix, while the splenium is in contact with the tela chorioidea. 



On either side, the fibers of the corpus callosum radiate in the white substance 

 nd pass to the various parts of the cerebral cortex; those curving forward from the 

 genu into the frontal lobe constitute the forceps anterior, and those curving backward 

 into the occipital lobe, the forceps posterior. Between these two parts is the main 

 body of the fibers which constitute the tapetum and extend laterally on either side 

 into the temporal lobe, and cover in the central part of the lateral ventricle. 



Fourth ventricle 

 FIG. 734. Scheme showing relations of the ventricles to the surface of the brain. 



The Lateral Ventricles (ventriculus lateralis) (Fig. 734) . The two lateral ventricles 

 are irregular cavities situated in the lower and medial parts of the cerebral hemi- 

 spheres, one on either side of the middle line. They are separated from each other 

 by a median vertical partition, the septum pellucidum, but communicate with the 

 third ventricle and indirectly with each other through the interventricular foramen. 

 They are lined by a thin, diaphanous membrane, the ependyma, covered by ciliated 

 epithelium, and contain cerebrospinal fluid, which, even in health, may be secreted 

 in considerable amount. Each lateral ventricle consists of a central part or body, 

 and three prolongations from it, termed cornua (Figs. 735, 736). 



The central part (pars centralis ventriculi lateralis; cello} (Fig. 737) of the lateral 

 ventricle extends from the interventricular foramen to the splenium of the corpus 



