THE CEREBRAL HEMISPHERES 



949 



AMYGDALA 



(head) and thalamus. The contour and slope of the surfaces of the ental pyramidal 

 face may be judged from the model pictured in Fig. 703. Its outline, as revealed 

 in sections passing in different planes, is shown in Figs. 701 and 704. 



Sections of the lenticular nucleus show it to be composed of three 1 concentric 

 segments separated by two white medullary laminae. The segments are known as 

 articuli; the ectal one is designated the putamen; the two ental zones constitute 

 the globus pallidus (paUiduni). The puta- 

 men is the larger and of a deeper reddish- 

 gray tint; the two mesal divisions are 

 lighter in color owing to a greater pro- 

 portion of radiating streaks of white 

 fibres passing to and from the internal 

 capsule. The ectal outline of the puta- 

 men is sharply defined against a white 

 lamina, the external capsule. 



The amygdaline nucleus (amygdala) 

 is usually regarded as an hypertrophied 

 aggregation of the temporal cortex which 

 has become nearly isolated from its 

 cortical connection by intruding white 

 substance. It is a rounded, gray, striated 

 mass situated in the fore part of the 

 temporal lobe in the roof of the middle 

 cornu at its apex, where it produces the 

 bulging called the amygdaloid tubercle. 

 ( 'audad it is joined by the tail of the 

 caudate nucleus; frontad it is continuous 

 with the putamen. Except for the 

 marked streaking shown in sections, 

 its structure is like that of the cortex. 

 Its cells apparently give rise to the narrow- 

 band of fibres the taenia semicircularis 

 which courses along the mesal margin of 

 the ventricular surface of the caudate nucleus throughout its arched course 

 and ends in the gray of the anterior perforated substance, so that it nearly 

 completes a circle. 



The claustrum is a thin plate of gray substance embedded in the white substance 

 which intervenes between the putamen and the cortex of the island of Reil. 

 and corresponds in extent to these. Its dorsal edge is very much attenuated; 

 traced ventrad it thickens considerably and becomes continuous with the surface 

 gray at the anterior perforated substance. Its ectal surface presents alternate 

 ridges and depressions which correspond to the corrugations of the cortex of the 

 island of Reil. The ''external capsule" intervenes between its ental face and 

 the putamen of the lenticular nucleus. From the cortex of the island of Reil 

 proper it is separated by a white lamina which may be termed the periclaustral 

 lamina or capsula extrema. Apparently the claustrum is the thickened and isolated 

 spindle-cell stratum of the cortex of the island of Reil, a feature which may be 

 of significance in relation to the preponderatingly associative function of the insular 

 region. 



Internal Capsule- (Fig. 704). Between the lenticular nucleus on the one hand 

 and the caudate nucleus and thalamus on the other lies the internal capsule, a broad 



1 Four and even five have been observed. 



- The terms internal capsule and external capsule own their derivation to the fact that the lenticular nucleus 

 is almost completely enveloped by white substance in the form of a capsule, of which the internal or mesal 

 portion, is relatively massive, while the external or lateral portion is thin. 



FIG. 703. Two views of a model of the striatum: A. 

 Lateral view aspect. B. Mesal view aspect. 



