60 ATLAS OF NERVE CELLS 



THE CORPUS STRIATUM 



THE corpus striatum of each hemisphere, a single mass of gray matter on the base of 

 the brain in its anterior part, is divided above into two parts, the caudate and lenticular nuclei, 

 by the passage downward of the fibres of the internal capsule. The caudate nucleus has a free 

 upper surface forming a part of the floor of the lateral ventricle. The lenticular nucleus is 

 surrounded on all sides by white matter, being bounded externally by the external capsule, in- 

 ternally by the internal capsule, and below by the lenticular loop. It is subdivided into an 

 external body or putamen, a median portion, the lobus intermedius, and an internal portion, 

 the lobus pallidus, by two bands of white fibres coursing through it from the internal capsule 

 to the lenticular loop. These relations are shown in Fig. 9, B, on page 52. 



Microscopical examination of the caudate and lenticular nuclei shows that they are essen- 

 tially alike in structure. They are made up of gray substance containing two varieties of cells; 

 very large rectangular cells and very small triangular or polygonal cells. These cells are 

 scattered indifferently through the mass of gray matter and are never collected into groups. 

 Plate XXXI. shows the large variety of cells characteristic of the corpus striatum. They are 

 70/1 long and 10 /u, to 15/11 broad. The body of the cell is long and narrow with a swell- 

 ing in its middle where the nucleus lies. At the extremities of the cell body dendrites are 

 given off, either one or two in number, and these appear to turn at right angles to the long 

 axis of the cell soon after leaving it. They give off very few branches and have a very long 

 course, being often traceable for a great distance through the gray matter and even into the 

 internal capsule. The neuraxon may arise from the body of the cell, but usually arises from 

 one of its protoplasmic prolongations near the body. It usually turns soon after its origin 

 toward the internal capsule, but does not uniformly arise from the side of the cell toward the 

 capsule. The majority of the neuraxons in the caudate nucleus enter the capsule from its 

 under surface. Those from the lenticular nucleus either pass into the lenticular loop by way 

 of the laminae, dividing the nucleus into its three parts, or else enter the capsule after travers- 

 ing the lobus pallidus. 



