638 



THE NEKVOUS SYSTEM. 



The nucleus lentiformis lies on the lateral side of the caudate nucleus and 

 thalamus, and is for the most part embedded within the white medullary sub- 

 stance of the cerebral hemisphere. It does not extend either so far forwards or 

 so far backwards as the caudate nucleus. Indeed, it presents a very close corre- 

 spondence in point of extent with the insula on the surface. When seen in hori- 

 zontal section, it presents a shape similar to that of a biconvex lens. Its medial 



surface bulges 

 more than the 

 lateral surface, and 

 its point of highest 

 convexity is placed 

 opposite the stria 

 terminalis and the 

 interval between 

 the caudate nuc- 

 leus and the thala- 

 mus. In frontal 

 section the appear- 

 ance presented by 

 the lentiform nuc- 

 leus differs very 

 much in different 

 planes of section. 

 Fig. 568 represents 

 a section through 

 its anterior por- 

 tion. Here it is 

 semilunar or cres- 

 centic in outline 

 and is directly 

 continuous below 

 with the head of 

 the caudate nuc- 

 leus ; above, also, 

 it is intimately 

 connected with the 

 caudate nucleus 

 by bands of gray 

 matter, which pass 

 between the two 

 nuclei and break 

 up the white 

 matter of the an- 

 terior part of the 

 intervening in- 

 ternal capsule. It 

 is due to the ribbed 



or barred appearance, which is presented by such a section as this, that the term 

 corpus striatum is applied to the two nuclei. In the region of the substantia 

 perforata anterior both nuclei reach the surface and become continuous with the 

 cortex. 



When a section is made in a plane further back (e.g. immediately posterior to 

 the anterior commissure, as in Fig. 569) the divided lentiform nucleus assumes an 

 altogether different shape, and is seen to be completely cut off from the caudate 

 nucleus by the internal capsule. It is now triangular or wedge-shaped. Its lase 

 is turned towards the insula and is in direct relation to a thin lamina of white 

 matter, termed the external capsule. Its medial surface is oblique and is applied 

 to the internal capsule, whilst its inferior surface is horizontal and is directed 

 downwards towards the base of the brain. But, further, two white laminae, the 



Genu of corpus callosum =_ 



Anterior horn of lateral 

 ventricle 



Caudate nucleus 



Anterior limb of internal 



capsule 



Cavum septi pellucidi 



Genu of internal capsule 



Columns of fornix 



Globus pallidus (of 



nucleus lentiformis) 



Fasciculus mamillo- 

 t-halamicus 



Posterior limb of internal 

 capsule 



Thalamus 



Retrolenticular part of 

 internal capsule 



Hippocampus 



Splenium 



Chorioid plexus 



Gyrus cingul: 



Calcarine sulcus 



Optic 

 radiation 



Tapetum 



Optic radia- 

 tion passing 

 back to 

 white line in 

 the area 

 striata 



FIG. 567. HORIZONTAL SECTION THROUGH THE RIGHT CEREBRAL HEMISPHERE 

 AT THE LEVEL OF THE WIDEST PART OF THE LENTIFORM NUCLEUS. 



