BASAL GANGLIA 469 



and the amygdaloid nucleus. In extent the claustrum corre- 

 sponds closely with the length and height of the insula. 



Nucleus Amygdalae. The amygdaloid nucleus lies partly 

 in the anteripji_jaU^pXjh^_antenor end ^of the inferior horn 

 of the lateral ventricle and partly in the adjacent portion of 

 the roof of the inferior horn. It is continuous with the tail 

 of the caudate nucleus ; with the antero-inferior part of the 

 putamen of the lentiform nucleus ; with the anterior perforated 

 substance, and with the grey matter of the piriform area of 

 the hippocampal gyrus. 



Nuclei of the Thalamus. When sections of the thalamus 

 are examined it will be noticed that it is surrounded, except 

 on its medial surface, by white matter. 



The thin layer of white matter on the superior surface is 

 termed the stratum zonale. It consists of fibres derived partly 

 from the optic tract and partly from the optic radiation of 

 the internal capsule. The white lamina on the lateral surface, 

 which separates the grey matter from the internal capsule, is 

 the external medullary lamina. The lower surface rests, 

 anteriorly, on the hypothalamus and the temporal peduncle 

 of the thalamus (p. 470) and posteriorly on the upper part of 

 the tegmentum of the cerebral peduncle. 



The grey matter of the thalamus is divided into three portions or nuclei 

 by the internal medullary lamina, which consists of a posterior stem and 

 two anterior branches. The portion of the thalamus which lies between 

 the two branches of the internal medullary lamina is the anterior nucletis. 

 It is connected with the mamillary body of the same side by the fasciculus 

 mamillo-thalamicus. The part of the thalamus lateral to the stem and the 

 lateral branch of the internal medullary lamina is the lateral nucleus. It 

 is longer than the medial nucleus and includes the whole of the posterior 

 end of the thalamus. The remaining part of the thalamus is the medial 

 nucleus ; it lies between the internal medullary lamina and the grey matter 

 of wall of the third ventricle, but extends, backwards, only as far as- the 

 trigonum habenube. 



The thalamus is connected with the cortex of the hemi- 

 sphere by bundles of fibres which are called the stalks or 

 peduncles of the thalamus ; they are the frontal, the parietal, 

 the temporal and the occipital. 



The frontal peduncle consists of fibres which emerge from 

 the antero-lateral part of the thalamus and pass, in the anterior 

 part of the internal capsule, to the frontal area of the cortex 

 of the hemisphere. The parietal peduncle springs from the 

 lateral part of the thalamus and passes partly through the 

 internal and external capsules, and partly, through the lentiform 

 in 30 a 



