642 THE NEKVOUS SYSTEM. 



Inferiorly it is continuous with the gray cortex of the piriform area, to which it is 

 functionally related, probably in the same way that the major part of the corpus 

 striatum is associated with the neopallium. 



Stria Terminalis. This is a band of fibres which, for the most part, arise in the 

 amygdaloid nucleus. From this it runs backwards in the roof of the inferior 

 horn of the lateral ventricle (Fig. 584, p. 657, and Fig. 573, p. 643), and then 

 arches upwards and forwards, so as to gain the floor of the pars centralis of the 

 lateral ventricle. In both situations it lies close to the medial side of the nucleus 

 caudatus, and finally, at the interventricular foramen, it bends downwards towards 

 the anterior commissure. Some of its fibres pass in front and others behind the 

 commissure, and ultimately they end in the neighbourhood of the substantia 

 perforata anterior (Kolliker). 



Internal Capsule. This term is applied to the broad band of white matter which 

 intervenes between the lentiform nucleus, on the lateral side, and the thalamus 

 and caudate nucleus on the medial side. It presents many different appearances, 

 according to the plane in which the brain is cut. A frontal section through the 

 brain which passes through the cerebral peduncles shows that, in great part, the 

 internal capsule is directly continuous with the basal part of the cerebral peduncle 

 (Fig. 580, p. 652). Viewed from the lateral aspect after removing all else of the 

 cerebral hemisphere excepting the corpus striatum (Fig. 573), the cut ends of the 

 fasciculi of the internal capsule form three-fourths of an ellipse, the other fourth 

 of which is occupied by the bridge of union between the lentiform and caudate 

 nuclei, the substantia perforata anterior, the amygdaloid nucleus and the anterior 

 commissure. It may be divided into an anterior (lenticulo-caudate) part, a superior 

 (lenticulo-thalamic) part, a retrolenticular part (not labelled in the figure), and a 

 postero-inferior (sublenticular) part. The last three parts are usually grouped 

 together as the posterior limb. In horizontal section the internal capsule is 

 observed to be bent upon itself opposite the stria terminalis, or the interval 

 between the caudate nucleus and the thalamus. This bend, which points medially, 

 is called the genu. About one-third of the internal capsule lies in .front of the 

 genu, and is termed the anterior limb ; the remaining two-thirds, which lie behind 

 the genu, constitute the posterior limb (Fig. 572). 



The anterior limb of the internal capsule intervenes between the lentiform 

 nucleus and the caudate nucleus. In its inferior and anterior* part it is much 

 broken up by the connecting bands of gray matter which pass between the anterior 

 part of the putamen and the caudate nucleus. 



The anterior limb of the internal capsule is composed largely of corticipetal fibres 

 belonging to the anterior thalamic radiation. It contains corticifugal fibres also. 

 The corticipetal fibres arise in the median and anterior part of the lateral nucleus of the 

 thalamus, and go through the anterior limb of the internal capsule to reach the cortex 

 of the frontal lobe. 



The corticifugal fibres are represented by the fronto-pontine tract. 



The fronto-pontine tract arises in the cortex of the frontal region, traverses the 

 anterior limb of the internal capsule, forms the medial fifth of the basis of the cerebral 

 peduncle, and finally ends in the nuclei pontis. 



The posterior limb of the internal capsule is placed between the thalamus and 

 the lentiform nucleus, and it extends backwards for a short distance beyond 

 the posterior end of the putamen on the lateral side of the posterior part of the 

 thalamus and of the tail of the caudate nucleus. The posterior limb, therefore, is 

 spoken of as consisting of a lenticular, a retrolenticular, and a sublenticular part. 



The lenticular or more properly lenticulo-thalamic part of the posterior limb is com- 

 posed of both corticipetal and corticifugal fibres. The corticipetal fibres enter the internal 

 capsule from the lateral aspect of the thalamus, and are composed of fibres which arise 

 within the thalamus from the ventral (ventro-lateral) nucleus, and proceed upwards to the 

 cerebral cortex. 



The corticifugal fibres consist of the cerebro-spinal tract and the cortico-thalamic fibres 



The great motor or cerebro-spinal tract, descending from the cerebral cortex 



occupies the anterior half of the lenticular part of the internal capsule. The fibres, that g< 



