BASAL GANGLIA. 



527 



into four more or less distinct masses termed nuclei, viz., an anterior, a 

 lateral, occupying the external part of the thalamus, a ventral, close to the 

 entire ventral surface, and a posterior, situated beneath the pulvinar. Be- 

 neath and somewhat internal to each optic thalamus there is a region, the 

 subthalamic, consisting of an intricate network of nerve-fibers and several 

 nuclei of gray matter, e.g., the red or tegmental nucleus, the subthalamic 

 nucleus, or Luys' body, and the substantia nigra. 



Though the thalamus has extensive connections with many portions of 

 the central nerve system, the most important are with the cortex, the teg- 

 mentum, and the optic tracts. 



From the cells of these various nuclei axons emerge which pass into the 

 internal capsule, and through the corona radiata to various portions of the 

 cortex. Those which come from the 

 pulvinar and pass to the occipital lobe 

 constitute a part of the optic radiation; 

 those from the lateral and ventral nuclei 

 ultimately reach the parietal lobe; those 

 from the anterior nucleus pass to the 

 hippocampal and uncinate convolutions. 

 In a similar manner various portions of 

 the cortex are brought into relation with 

 the thalamus, axons from the cortical 

 cells passing downward to terminate in 

 tufts around the thalamic nuclei. 



The tegmentum is intimately related 

 to the thalamus, though the exact dis- 

 tribution of various strands of fibers is 

 a subject of much discussion. Most 

 of the fibers of the mesial fillet end in 

 tufts around the cells of the ventral and 

 lateral nuclei; other fibers pass directly 

 to the cortex. 



The optic tract sends fibers directly 

 into the pulvinar, the external geniculate 

 body, and the superior corpus quadri- 

 geminum, around the cells of which they 

 terminate in brush-like expansions. 



The Internal Capsule. The lenti- 

 cular nucleus is enclosed on all sides 

 by ascending and descending nerve-fibers. From the manner in which 

 they surround and enclose the nucleus they have collectively been called the 

 lenticular capsule. If a horizontal section of the cerebrum be made at a 

 certain level so as to cut across the capsule and the enclosed nucleus an 

 appearance similar to that shown in Fig. 244 will be presented. That portion 

 of the capsule that lies between the caudate nucleus and the optic thalamus 

 internally and the lenticular nucleus externally is known as the internal 

 portion of the lenticular capsule or in its abbreviated form as the internal 

 capsule, while that portion between the external convex border of the len- 

 ticular nucleus and the claustrum is known as the external portion of the 



AMYGDALA 



FIG. 243. Two VIEWS OF A MODEL 

 OF THE STRIATUM. A, Lateral aspect; B, 

 mesial aspect. (Spitzka.) 



