1869.] 



of the Cerebral Hemispheres. 



57 



The extra-ventricular part of the thalamus is seen in the descending 

 cornu curving round the crus. From its anterior pointed extremity it is 

 continued onwards hy the optic tract, and it sends fibres, — 1. Forwards in 

 the collar of the crus. 2. Forwards and outwards to the convolutions 

 about the apex in a succession of lamina?, the deeper fibres passing more 

 outwards than the superficial sets, and emerging from under them along 

 the outer edge of the roof of the cornu. 3. From under the fibres which 

 pass forwards, it sends backwards a large mass along the outer wall of the 

 veutricle and posterior cornu to the occipital end of the hemisphere. 



The extraventricular corpus striatum has been exposed on two sides ; it 

 forms a very large mass, and has a large rounded anterior end, while pos- 

 teriorly it narrows to a tail-like extremity. The outer aspect forms an 

 elongated eminence, rising out of the Sylvian valley, highest at the centre, 

 subsiding towards each end ; at the summit is the external grey nucleus, 

 from which radiate fibres forwards, backwards, and outwards. Those 

 passing forwards form a large bundle ; they spread out into a fan, and 

 proceed mainly to the third frontal convolution ; those passing backwards 

 accompany the fibres from the thalamus to the occipital extremity of the 

 hemisphere ; those passing outwards with varying degrees of obliquity 

 descend the wall of the ganglion to the Sylvian valley ; but instead of 

 crossing it to the convolutions on the other side, as might be expected 

 from the apparent continuity of the walls and floor, dip between the fibres 

 of the floor, which are the radiating fibres of the crus issuing from the 

 C. striatum, and pass to convolutions in the frontal lobe. A remarkable 

 fact respecting the planes of radiating fibres which form the limiting wall 

 of the C. striatum on this aspect is, that the fibres ail seem to have their 

 origin in the small patch of grey matter here called the external grey 

 nucleus, and they come off clean from the mass of soft grey matter forming 

 the body of the ganglion. 



On the under surface of the C. striatum, which is flat, are seen the 

 internal grey nucleus and the anterior perforated space, between which the 

 anterior commissure passes outwards and backwards from the ventricle in 

 a distinct canal to emerge on this surface. The external grey nucleus also 

 appears in the outer border, and is about in the same transverse line as the 

 C. albicans and internal grey nucleus, from which last it is only separated 

 by a narrow band of longitudinal fibres. Here again the planes of fibres, 

 which form the limiting wall of the ganglion, end in the grey nuclei, and 

 seem to have no communication with the mass of soft grey matter they 

 inclose. 



The anterior edge of the fan-like expansion of the crus emerges from 

 the large end of the C. striatum, and, properly speaking, divides the 

 intra-ventricular C. striatum from the extra-ventricular division ; the an- 

 terior perforated space, being on the inner side of the radiating fibres, 

 belongs to the former. 



Before the dissection of the fronto-parietal portion of the hemisphere is 



