468 THE BRAIN 



and an antero-medial and a postero-medial surface (Figs. 

 182, 191). 



The posterior part of the inferior surface lies above the 

 inferior horn of the lateral ventricle, from which it is separated 

 by some white matter and by the tail of the caudate nucleus 

 and the stria terminalis (Fig. 188). More anteriorly the 

 inferior surface rests upon the white matter of the temporal 

 lobe of the hemisphere, and still more anteriorly it fuses with 

 the grey matter of the anterior perforated substance (Fig. 186). 

 Curving backwards and laterally in a groove on the lower 

 surface of the lentiform nucleus lies the twisted bundle of 

 fibres of the anterior commissure, on its way to the temporal 

 lobe (Fig. 189). 



The lateral surface is convex and is in relation, in the 

 whole of its extent, with a layer of white matter, called the 

 external capsule, which separates it from the claustrum. 



The antero-medial and the postero-medial surfaces are in 

 relation with the internal capsule, and the medial angle which 

 separates the two surfaces lies in a bend of the capsule which 

 is called the genu (Figs. 182, 191). 



Passing vertically through the lentiform nucleus and 

 dividing it into three parts are two white layers called the 

 medullary laminae. As already stated, the medial two parts 

 are lighter in colour than the lateral part; they constitute the 

 globus pallidus. The lateral part is the putamen. 



The antero -inferior part of the lentiform nucleus is 

 continuous with the head of the caudate nucleus and the 

 anterior perforated substance (Fig. 186), but in the remainder 

 of its extent the lentiform nucleus is surrounded by the white 

 matter of the hemisphere. 



The lentiform nucleus is associated with the cortex of 

 the hemisphere, with the thalamus, and with other adjacent 

 parts, by white nerve fibres which pass to and from the 

 nucleus. 



Claustrum. The claustrum is a thin plate of grey matter 

 which lies between the external capsule and the white matter 

 of the insula. Its medial surface, which is relatively smooth, 

 is separated from the lateral surface of the lentiform nucleus 

 by the external capsule. Its lateral surface is scalloped, the 

 elevations and depressions corresponding with the gyri and 

 sulci of the insula. Its lower border, which is its broadest 

 part, is fused, anteriorly, with the anterior perforated substance 



