386 DISSECTION OF THE BABBIT. 



press the hemispheres apart : note the position of the corpus 

 callosum^ 



Then, with the back of a knife, peel off the portion of the 

 right hemisphere lying above the corpus callosum. Keep the 

 brain wet with spirit. 



i. The corpus callosum is a broad horizontal band 

 of fibres connecting the two hemispheres. 



ii. The structure of the hemisphere. 



a. The outer layer or cortex is a superficial invest- 

 ment of grey matter, about an eighth of 

 an inch thick. 



(i. The central or medullary portion consists of 

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

 The fibres of the corpus callosum spread out 

 into, and are continuous with it. 



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



Gut 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, leaving a narrow 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 cornu ; 

 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. 



