766 



DISSECTION >OF THEi BRAIN. 



Lining of 

 cavity. 



Grey matter 

 of the 

 ventricle. 



Corpus 

 striatum, 



structure. 



Dissection. 



Caudate 

 nucleus 

 shows in 

 lateral 

 ventricle : 



veins on 

 surface. 



Lenticular 

 nucleus is 

 only seen in 

 sections ; 



surrounded 

 by white 

 capsule., . 



depression opposite the infundibulum, where the cavity at an early- 

 period of foetal life was prolonged into the pituitary body. 



The ependyma lining the ventricle is continued into the neigh- 

 bouring cavities through the different apertures of communication, 

 and its epithelium is continued over the choroid plexuses in 

 the roof. 



Grey matter of tlie ventricle. A stratum of grey matter forms the 

 lower part of the wall of the ventricle. Portions of this layer 

 appearing at the base of the brain constitute the posterior per- 

 forated space, the tuber cinereum and the lamina cinerea. It also 

 extends into the corpus albicans, forming the nucleus of that body. 

 At the fore part of each optic thalamus it covers the pillar of the 

 fornix, and ascends to the septum lucidum. In the middle of the 

 space it reaches from side to side, and forms the middle or soft 

 commissure (d). 



The CORPUS STRIATUM is the large grey body a part of which has 

 been seen in the floor of the lateral ventricle. The grey matter 

 composing it is incompletely divided into two masses caudate and 

 lenticular nuclei, by a layer of white fibres, named the internal 

 capsule ; and it has received its name from the striated appearance 

 of this layer. The caudate nucleus, as already seen (fig. 275, e), is 

 intraventricular in position, whilst the lenticular is extraventricular 

 and requires further dissection to expose it. 



Dissection. To show the composition of the corpus striatum, 

 the upper part of that body and of the optic thalamus should be 

 sliced off horizontally on the right side, until a view resembling 

 that in fig. 278 is obtained. The superficial anatomy of the 

 corpus striatum and optic thalamus may be studied on the left side 

 at the same time by comparison. 



The caudate or intraventricular nucleus (fig. 277, a) is a long 

 pyriform mass of reddish-grey substance which projects into the 

 lateral ventricle. Its larger extremity or head (fig. 278, en) is 

 turned forwards, and forms the floor and outer wall of the anterior 

 cornu of the ventricle. The middle tapering portion is directed 

 backwards and outwards, along the outer side of the optic thalamus, 

 beneath the body of the ventricle, and ends in the tail (fig. 278, en'), 

 which bends downwards and is prolonged in the roof of the descend- 

 ing cornu of the cavity nearly to its anterior extremity. Numerous 

 veins run over the surface of the caudate nucleus, and they may be 

 seen to join a larger vessel (vein of the corpus striatum) which lies 

 along the groove between the caudate nucleus and the optic thalamus. 



The lenticular or extraventricular nucleus is entirely surrounded 

 by white matter, and is placed opposite the bottom of the fissure of 

 Sylvius, corresponding to the Island of Reil on the exterior. It 

 appears lens-shaped in horizontal section (fig. 278, In), but triangular, 

 with the base turned outwards, when cut transversely (fig. 279, 

 p. 768). Internally, it is separated from the caudate nucleus 

 and optic thalamus by the internal capsule (fig. 278, ica to icp) ; 

 and externally and below, it is bounded by a thinner white layer 

 named the external capsule (ec). 



