STRUCTURAL ARRANGEMENTS OF CEREBRUM 475 



mater, including the choroid plexus. On removing this the third 

 ventricle is opened, so that in this region the wall of the cerebral hemi- 

 spheres, like the roof of the third ventricle, is limited to a simple layer 

 of ependyma. At the margin of the choroid plexus can be seen 

 a part of the superior surface of the optic thalamus, separated, however, 

 from the cavity of the ventricle by a layer of ependyma. Outside 

 and in front of the optic thalamus are the masses of nervous 

 material constituting the cor- 

 pus stria turn. These present 

 two nuclei of grey matter, 

 known as the nucleus cau- 

 datus and the nucleus lenticu- 

 laris (Fig. 211). The crusta 

 of the crura cerebri as it 

 ascends to the cerebral hemi- 

 spheres passes behind between 

 the optic thalamus and the 

 corpus striatum. and in front 

 between the nucleus lenticu- 

 laris and nucleus caudatus of 

 the corpus striatum. Outside 

 the corpus striatum we find 

 another mass of white fibres, 

 known as the external capsule, 

 and this is separated from the 

 white matter of the cortex 

 cerebri by a thin layer of grey 

 matter known as the claus- 

 trum. In a horizontal section 

 through the brain, the part 



of the internal capsule which 

 pierces the corpus striatum 

 forms an angle with the pos- 

 terior part separating the optic 

 thalamus from the lenticular 

 nucleus." The part where the 

 two limbs come in contact is 

 known as the genu of the 

 internal capsule. 



FIG. 211. Horizontal section through the 

 ljft optic thalamus and corpus striatum, 

 the 'basal ganglia.' (Natural size.) 



vl, lateral ventricle, its anterior cornu ; 

 cc, corpus callosum ; si, septum lucidum ; 

 af, anterior pillars of the fornix ; v3, third 

 ventricle ; th, thalamus opticus ; st, stria 

 medullaris ; nc, nucleus caudatus, and 

 ril, nucleus lenticularis of the corpus stria- 

 tum ; ic, internal capsule ; g, its angle or 

 genu ; nc, tail of the nucleus caudatus 

 appearing in the descending cornu of the 

 lateral ventricle ; cl, claustrum ; 7, island 

 of Reil. 



THE OLFACTORY APPARATUS OF THE BRAIN 

 In man the olfactory sense is but feebly developed, and the parts 

 of the brain connected therewith are inconspicuous in comparison 

 with those engaged in the reception of impressions from the other two 



