BASAL GANGLIA. 525 



of the fibers of the optic tract, though it is not probable that they are true visual 

 fibers. Still other cells receive the terminal branches of axons the cells of 

 origin of which are located in the occipital cortex of the cerebrum and which 

 reach the superior quadrigeminal body by way of the optic radiation and 

 internal capsule. 



The cells of the post-geminum give origin to axons which pass upward, 

 forward, and outward, enter the internal capsule, and pass by way of the 

 auditory tract to the cortex of the temporo-sphenoidal region of the cerebrum. 

 Many of the fibers of the lateral fillet, a portion of the auditory tract, termi- 

 nate in brush-like expansions around these same cells. There is thus es- 

 tablished a connected pathway between the cochlea and the temporo-sphe- 

 noidal cortex. The cells of the temporal cortex, however, send axons in the 

 reverse direction by way of the auditory tract to the cells of the post-geminum. 

 There is thus established a double communication between the occipital 

 and temporal region of the cerebral cortex, and the pre-geminal and post- 

 geminal bodies respectively. 



THE BASAL GANGLIA; THE CORPORA STRIATA AND OPTIC 



THALAMI. 



The basal ganglia are collections of ganglionic matter, situated at the 

 base ot the cerebrum along the course of the nerve-fibers that pass to and 

 from its cortical expansion. Among these ganglia the more important are 

 the corpora striata and the optic ffialami. They are made visible upon 

 removal of the cerebrum. The general relations of these ganglia are shown 

 in Fig. 242. 



The corpus striatum, the more anterior of the two, is an ovoid col- 

 lection of gray and white matter and receives its name from the fact that it 

 presents on cross-section a striated appearance. The larger portion of this 

 body is embedded in the cerebral white matter, while the smaller portion 

 projects into the anterior part of the lateral ventricle. A dissection of this 

 nucleus shows that it is subdivided by a band of white matter into two 

 smaller nuclei, viz, the caudate and the lenticular nuclei. 



i. The caudate nucleus is a pyriform body which corresponds with the 

 intra-ventricular portion of the corpus striatum. It consists of a head, 

 an arching body and a tail. The head, which is thick and large, projects 

 into the anterior cornu of the ventricle; the body arches across the ven- 

 tricle from before backward and from within outward, while the tail is 

 directed downward and forward to become associated with the collection 

 of gray matter situated beneath the lenticular nucleus and known as the 

 amygdaline nucleus. Anteriorly the caudate nucleus, is united with the 

 lenticular nucleus by a narrow bridge of gray matter, partially subdivided 

 by small bands or strands of nerve fibers passing through it. 



2.\The lenticular nucleus is an irregularly triangular pyramidal-shaped body 

 and corresponds with the extra-ventricular portion of the corpus striatum, 

 the portion embedded in the cerebral white matter. The apical extremity 

 of the nucleus is directed toward the median line while its convex base 

 is directed toward and runs almost parallel with the gray matter of the 



