MEDULLA AND BASAL GANGLIA 573 



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 

 distribution 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 quadrigeminum, around the cells 

 of which they terminate in brush-like expansions. 



The Internal Capsule. The lenticular 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. 238 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 

 lenticular capsule or in its abbreviated form as the external capsule. At a 

 given level the internal capsule may be said to consist of two segments or 

 limbs, an anterior, situated between the caudate nucleus and the anterior 

 extremity of the lenticular nucleus, and a posterior, situated between the 

 optic thalamus and the posterior extremity of the lenticular nucleus. The 

 two segments unite at an obtuse angle, termed the knee, which is directed 

 toward the median line. The appearance which is presented at different 

 levels varies however considerably. 



SUMMARY OF THE STRUCTURE OF THE MEDULLA, ISTHMUS, AND 



BASAL GANGLIA 



Structure of the Central Gray Matter. Though the general arrange- 

 ment of the central gray matter has been incidentally alluded to in the fore- 

 going presentation of the anatomic features of the medulla and isthmus, it 

 will be convenient to summarize its arrangement and structure at this point. 



The gray matter of the cord, of the dorsal aspect of the medulla and pons, 

 of the region surrounding the aqueduct of Sylvius, and of the lining of the 

 third ventricle, constitute practically a continuous system, though presenting 

 modifications in various parts of its extent. In the transition region of the 

 spinal cord and medulla the gray matter of the former becomes much changed 

 in shape owing to the shifting of position of the various tracts of white matter, 



