THE FOKE-BKAIN 



529 



In the higher vertebrates (birds and mammals) the basal 

 ganglion undergoes a further subdivision ; the fibres which 

 descend from the pallium traverse it, dividing it into a lateral or 

 extra ventricular and a medial or iutra ventricular segment. The 

 first is generally known as the lenticular nucleus ; the second as 

 the caudate nucleus (Figs. 245, 246, 247). Both these nuclei of the 

 corpus striatum are united by 

 fibres to the nuclei of the optic 

 thalamus. 



The caudate nucleus of the 

 human brain is pear-shaped 

 with the larger end anteriorly, 

 it lies in the wall of the anterior 

 horn of the lateral ventricle. 

 Its ventricular surface is 

 covered by a layer of ependyma 

 and of ciliated epithelium. The 

 mass of the ganglion consists 

 of a reddish -grey substance; 

 the microscope shows nerve- 

 cells generally pigmented in 

 the adult, most of which are 

 small and belong to Golgi's 

 second type with short axis- 

 cylinder processes running in 

 various directions, some into 

 the internal capsule (Marchi). 



The lenticular nucleus is 

 separated from the caudate 

 nucleus by the layer of white 

 matter which forms the in- 

 ternal capsule. It is only 

 visible in sections of the hemi- 

 sphere (Fig. 263), in which it 

 appears lens -shaped. It is 

 smaller at both ends than the 

 caudate nucleus. Two white 

 lines or medullary laminae divide it into three zones, the outer 

 of which, the largest and dark red in colour, is known as the 

 putamen; the two inner, of a yellower tint, are known as the 

 globus pallidus. Anteriorly these two nuclei of the corpus 

 striatum are united by their bases, and come into contact below 

 with another nodule of grey matter, the nucleus amygdalus, which 

 in its turn is continuous with the grey matter of the cortex. 

 The cells of the lenticular nucleus contain yellow pigment, and as 

 a whole resemble those of the caudate nucleus, but many of them 

 belong to Golgi's first type i.e. they have long axis-cylinders. 



VOL. in 2 M 



Fio. 262. Frontal section through fore-brain of a 

 teleostean, Corvina nigra, directed obliquely 

 behind and down. Round this the outline of 

 a mammalian cerebrum is drawn, to show the 

 relations between the basal ganglia and the 

 pallium. (Bdinger.) 



