THE BKAIX AXD ITS 



759 



floor, presents for examination the following parts: the hippocampus major, pes 

 hippocampi, eminently <.;>Uuteralis or pes accessorius, and corpus fimbriatum from 

 the for nix. The o//f> r "-all is white matter of the temporal lobe. The inner icall 

 is a layer of epithelium, prolonged from that covering the pulvinar, just mentioned, 

 which is ini'ii'iiii'iti'd by a fold of pia mater, and thus is formed the choroid plexus. 

 The corpus striatum (Fig. 450) has received its name from the striped appear- 

 ance which its section presents, in consequence of diverging white fibres being 

 mixed with the gray matter which forms the greater part of its substance. The 

 greater portion of this body is imbedded in the white substance of the hemisphere, 

 and is therefore external to the ventricle. It is termed the extraventricular por- 



FIG. 450. Middle part of a horizontal section through the cerebrum at the level of the dotted line in the 

 small figure of one hemisphere. (From Ellis, after Dalton). 



tion, or the nucleus lenticularis : a part, however, is visible in the ventricle and 

 its anterior cornu; this is the intraventricular portion, or the nucleus caudatus. 

 The intra ventricular portion is a pear-shaped mass of gray matter : its broad ante- 

 rior extremity is the convex outer wall of the anterior cornu. Its narrow end is 

 directed backward, and lies on the outer part of the floor of the body of the ven- 

 tricle. It is continued, by a sharp anterior bend, into the roof of the descending 

 cornu : it is covered by the lining of the cavity and crossed by some veins of 

 considerable size. It is separated from the extraventricular portion by a lamina 

 of white matter, the internal capsule, in contradistinction to a lamina of white 

 matter which covers the outer surface of the extraventricular portion of the corpus 

 striatum, and which is called the external capsule. 



The extraventricular portion of the corpus striatum, or nucleus lenticularis, 

 is oval in form. It does not extend as far forward or backward as the nucleus 



