THE TELENCEPHALON. 



171 



by the internal medullary lamina and form the edge of the wedge, lying in contact 

 with the internal capsule. Although composed chiefly of gray matter, all these 

 segments of the nucleus, but particulary the inner two, are traversed by numerous 

 strands of nerve-fibres which break the continuity of the gray substance and produce 

 an appearance of radial striation. 



The structure of the corpus striatum varies in its several parts, that of the 

 caudate nucleus and the putamen being almost identical, whilst that of the globus 

 pallidus, although similar in both zones, differs from the histological make up of the 

 other parts. The close resemblance of the caudate nucleus and the putamen corre- 

 sponds to their early common origin, since at first they constitute a single mass and 

 become partially separated by the ingrowth of the fibres forming the anterior part of 

 the internal capsule. 



The caudate nucleus is invested throughout the greater part of its periphery 

 by a dense layer of fibres, the stratum zonale, which includes fibres passing both to 



FIG. 1010. 



Corpus callosui 

 Choroid plexus 



Fornix 



Thalamus, 

 mesial nucleus 



Thalamus, 

 lateral nucleus 



Mammillo- 

 thalamic tract 



Third ventricle 



Anterior pillar 

 of fornix 



Optic tract 



Caudate nucleus 



Internal capsule 



Lenticular 

 nucleus, putameu 



Insula 



Globus pallidus 



Claustrum 



Amygdaloid nucleus 



Pituitary body Optic nerve 



Frontal section of brain passing through caudate and lenticular nuclei and thalamus, showing relation of internal 



capsule to internal nuclei. 



and from the nucleus. The nerve-cells are, for the most part, rather small in size 

 and stellate or fusiform in shape and provided with numerous dendrites beset with 

 minute irregularities. They are chiefly cells of type I, although many of the second 

 type are encountered, whose axones are limited to the gray matter and are not 

 prolonged as nerve-fibres (Kolliker). 



The putamen is invested on its two sides, particularly on the mesial one, with a 

 fibre-layer derived from the external medullary lamina and the external capsule, the 

 fibres being chiefly such as enter the nucleus from other centres by way of the med- 

 ullary layer. In addition to nerve-cells of round or stellate form, Kolliker describes 

 those of distinctive appearance possessing a slender fusiform body and dendrites few 

 in number but of unusual length. 



The globus pallidus owes its characteristic color to the light yellowish tint of 

 the pigment within its cells and to the large number of medullated nerve-fibres which 

 traverse its substance, especially its inner zone. The nerve-cells are mostly small 

 and stellate, possessing numerous short but richly branched dendrites. 



