THE BRAIN. 499 



Crura cerebri, also called the peduncles of the cerebrum, are 

 made up of white matter, nerves which are continuous with those 

 already studied in the medulla and pons, together with nerves 

 from the cerebellum, the superior peduncles. Between the super- 

 ficial fibers of the crura, the crusta, and the deeper ones, the teg- 

 mentum f is the locus niger, a collection of gray matter. The 

 fibers of the crura on their way upward to the gray matter of the 

 hemispheres pass through the corpora striata and the optic 

 thalami. 



Basal Ganglia. At the base of the hemisphere are certain 

 bodies, the basal ganglia, which are the corpora striata, the optic 



co. 



FIG. 290. Vertical section through the cerebrum and basal ganglia to show the 

 relations of the latter: co., cerebral convolutions; c.c., corpus callosum; v.l., lateral 

 ventricle ; 6., fornix ; vIIL, third ventricle ; n.c., caudate nucleus ; th, optic thala- 

 mus; n.l., lenticular nucleus; c.L, internal capsule; cl, claustrum; c.e., external 

 capsule ; m, corpus mammillare ; t.o., optic tract ; s.t.t., stria terminalis ; n.a., nucleus 

 amygdalae; cm, soft commissure ; co.i, island of Reil (Schwalbe). 

 > 



thalami, the tubercula quadrigemina or corpora quadrigemina, the 

 corpora geniculata, and the locus niger. 



Corpora striata, with the optic thalami, are called the cerebral 

 ganglia. The corpora striata present a striped appearance, which 

 is due to a mixture of gray and white matter, the latter being 

 bundles of fibers which have come from below and within-. 

 Although at the lowest part each corpus striatum is a single body, 

 at the upper part it is divided into two portions, the caudate 

 nucleus and lenticular nucleus. The lenticular nucleus, the more 

 posterior, is separated from the optic thalamus by white matter, 

 the internal capsule, which is the continuation of the crus cerebri. 

 Outside the lenticular nucleus is white matter, the external cap- 

 sule, beyond which is a layer of gray matter, the claustrum, and 



