THE BEAIN 359 



/3. The central or medullary portion consists of 

 white matter, i.e. of meduUated nerve-fibres. 

 The fibres of the corpus caUosum spread out 

 into, and are continuous with it. 



iii. The lateral ventricle, or cavity of the hemisphere. 



Cut through the corpus callosum on the right side, so as 

 to open the lateral ventricle beneath it. Lift up the corpus 

 callosum, and carefully cut it away, so as to expose the ven- 

 tricle fully, lea/ving a na/rrow strip along its inner edge. 



The lateral ventricle, opposite the middle 

 of the hemisphere, is wide from side to side, 

 but shallow dorso-ventrally. Anteriorly, it 

 extends forwards as a narrow vertical slit, 

 the anterior cornu, which lies nearer the inner 

 than the outer surface of the hemisphere. 



Posteriorly, the lateral ventricle curves 

 backwards and inwards towards the hinder 

 end of the hemisphere as the posterior coma ; 

 and from its outer side, a little behind the 

 middle of the hemisphere, a descending 

 cornu runs outwards and downwards, and 

 then curves round in the temporal lobe to the 

 ventral region, running forwards and inwards 

 almost to the anterior end of the lobe, and 

 ending opposite the infundibulum. 



Open up the descending cornu along its whole length, by 

 carefully cutting away the outer and ventral walls of the 

 temporal lobe. 



iv. The hippocampus major is a prominent convex 

 ridge, projecting into the floor and inner side 

 of the descending cornu, along its whole 

 length. 



V. The corpus striatum is a thickened part of the 

 wall of the hemisphere, forming the outer side 

 and floor of the anterior part of the lateral 



