880 



THE NERVOUS SYSTEM 



ther forward, the anterior commissure passes through its base. Its lateral sur- 

 face is rounded and conforms both in extent and curvature with the surface of the 

 insula, from which it is separated by the fibres of the external capsule and the 

 intervening claustrum. Its oblique superior and mesial surface is adapted to the 

 lateral surface of the internal capsule, and it comes to a rounded apex in the angle 

 formed by the internal capsule and a plane parallel with the base of the hemi- 

 sphere. In both horizontal and coronal (transverse) sections through its middle 

 it resembles a compound biconvex lens. Internally this appearance is produced 

 by two vertically curving laminae of white substance, an external and an internal 

 medullary lamina, which divide its substance into three zones: — the two medial 

 zones together form an area, triangular in section, known as the globus pallidus ; 

 the lateral, larger and more grey, concavo-convex zone is the putamen. Radiat- 

 ing fibres from the medullary laminae extend into the zones, especially those of the 

 globus palhdus. These zones disappear in transverse sections of the anterior 



Fig. 692. — Coronal Section of Telencephalon Passing Through Frontal Lobes and 



Anterior Portion op Corpus Striatum. 



(From mounted specimen in the Anatomical Department of Trinity College, Dublin.) 



Longi- 

 ^^— - tudinal 

 \y fissure 



Lenticular 



nucleus 

 Claustrum 



Longi- 

 tudinal 

 fissure 



Olfactory tract 



portion of the lenticular nucleus (fig. G92), due to the fact that the larger putamen 

 alone comprises this portion and alone becomes continuous Avith the caudate 

 nucleus. (See fig&. 691, 696.) 



Connections. — Both nuclei of the corpus striatum become continuous with the cortex in 

 the region of the anterior perforated substance, and the putamen of the lenticular nucleus may 

 blend with the anterior part of the base of the claustrum. The following are the principal fibre 

 connections: — (1) Fibres arising in the nuclei which join the internal capsule to reach the 

 cerebral corte.x, and fibres arising in the cortex which descend by the same course to the cells 

 of the nuclei. (2j Fibres which pass in both directions between the thalamus and the corpus 

 striatum (caudate nucleus especially). These are more abundant anteriorly, and necessarily 

 pass through the internal capsule. (.3) The ansa lenticularis, or strio-subthalamic radiation, 

 a usually distinct lamina, composed largely of fibres passing inferiorly between the thalamus 

 and lenticular nucleus. It passes from the basal aspect of tiie anterior tubercle of the thalamus 

 and (;urv('s Ix-low through the internal capsule to the basal surface of the lenticular nucleus, 

 and there its fibres are distributed upward through its medullary lamina to the globus pallidus 

 and putamen. Some enter the internal cai)sule :ind reacli the cortex, chiefly that of the tem- 

 poral lobe. ''J'he ansa lenticularis also contains fibres from the cortex of the temporal lobe to 

 terminate in the inferior and mesial parts of t lie thalamus. The fibres associating the thalamus 

 with the temporal IoIjc belong to the so-called inferior peduncle of the thalamus. (4) Fibres 

 connecting both nuclei (chiefly the caudate) with the red nucleus and substantia nigra of the 

 mesencephalon. These pass through the hypothalamic region and along the cerebral peduncle. 

 No definitely localised functions have been with certainty ascribed to eitlier nucleus. They 

 serve as relays in the patliways associating the cortical grey substance with tlie structures below 

 and in them t he neurones concerned in tlu^se pathways are greatly increased. 



The claustrum is a triangular plate of grey substance which is embedded in 

 the white substance between the lenticular nucleus and the insula. Its medial 



