THE BRAIN 349 



between the right and left hemispheres. It 

 lies below the corpus callosum and above the 

 fornix, and is bounded laterally by the septum 

 lucidum of the right and left sides. 



It is merely a part of the space between 



the two hemispheres, partially enclosed by the 



corpus callosum and the fornix ; and is not, 



properly speaking, a ' ventricle ' at all. 



To expose the fifth ventricle from above, carefully remove 



the narrow strip of the corpus callosum that has been left 



along its inner side, and the fifth ventricle will be seen as a 



narrow cleft between the two hemispheres. 



X. The Mppocampal sulcus is a deep groove on tbe 



surface of the temporal lobe. It gives rise to 



the inwardly projecting fold of the hemisphere 



which forms the hippocampus major. 



Bemove the temporal lobe completely, and the Mppocampal 



sulcus will be seen on its inner swrface. 



b. The fore-brain, or thalamencephalon. 



i. The optic thalami are a pair of large lateral 

 thickenings of the sides of the fore-brain, 

 placed immediately in front of the optic lobes, 

 and overlapped by the temporal lobes of the 

 hemispheres. They are separated by grooves 

 from the corpora striata in front, and the optic 

 lobes behind. 



On the outer and ventral surface of each 

 optic thalamus, near its anterior end, is a 

 rounded elevation, the corpus geniculatum. 

 ii. The optic tracts are a pair of narrow bands, 

 which can be traced backwards and upwards 

 from the outer ends of the optic chiasma, 

 over the surface of the optic thalami, to the 

 anterior borders of the optic lobes. 

 Take hold of the anterior end of the right optic tract with 

 the forceps, and strip it off the optic thalamus, so as to see its 

 origin from the optic lobe. 



