CH. XLVL] 



CEREBRAL HEMISPHERES 



653 



plicated shape called the lateral ventricle ; the lateral ventricles open 

 into the third ventricle. Fig. 475 represents a dissected brain in which 

 the corpus callosum has been removed; the ventricles are thus 

 exposed. 



Each hemisphere is covered with grey matter, which passes down 



FIG. 475. Dissection of braiii, from above, exposing the lateral, fourth, and fifth ventricles with the 

 surrounding parts. . a, anterior part, or genu of corpus callosum ; b, corpus striatum ; &', the 

 corpus striatum of left side, dissected so as to expose its grey substance ; c, points by a line to the 

 tsenia semicircularis ; d, optic thalamus; e, anterior pillars of fornix divided; below they are seen 

 descending in front of the third ventricle, and between them is seen part of the anterior commis- 

 sure ; in front of the letter e is seen the slit-like fifth ventricle, between the two laminae of the 

 septum lucidum ; /, soft or middle commissure ; g is placed in the posterior part of the third 

 ventricle ; immediately behind the latter are the posterior commissure (just visible) and the pineal 

 gland, the two crura of which extend forwards along the inner and upper margins of the optic 

 thalami ; h and i, the corpora quadrigemina ; fc, superior crus of cerebellum ; close to k is the valve 

 of Vieussens, which has been divided so as to expose the fourth ventricle ; I, hippocampus major 

 and corpus fimbriatum, or tsenia hippocampi ; m, hippocampus minor ; n, eminentia collaterals ; 

 o, fourth ventricle ; p, posterior surface of medulla oblongata ; r, section of cerebellum ; s, upper part 

 of left hemisphere of cerebellum exposed by the removal of part of the posterior cerebral lobe. 

 (Hirschfeld and Leveille.) 



into the fissures. This surface grey matter is called the cerebral 

 cortex. The amount of this grey matter varies directly with the 

 amount of convolution of the surface. Under it white matter is 

 situated ; and at the base there are masses of grey matter ; part of 

 these "basal ganglia are seen forming part of the wall of the ventricles. 

 The anterior basal ganglion is called the corpus striatum; it is 



