350 ANATOMY OF THE CENTHAL NERVOUS SYSTEM. 



corresponding fibers of the corona radiata passing to the thalamus, and the 

 frontal fibers passing to the pons. 



In order to pass into the thalamus and the pons, this mass of fibers must 

 cut through the ganglion of the corpus striatum, which lies in the way 

 (Fig. 160). The part which lies nearer the median line is the aforesaid 

 nucleus caudatus; the part that comes to lie more external is the nucleus 

 lenliformis. Xevertheless, thej' are not absolutely separated from one an- 

 other by the fibers from the frontal lobes; numerous connecting fibers pass 

 between them. The above-mentioned fibers of the corona radiata to the 

 thalamus, the fibers from the frontal lobe to the pons, the bundles between 

 the head of the nucleus caudatus and the nucleus lentiformis, and, finally, 

 other fibers from the nucleus caudatus to the thalamus and to the nucleus 

 lentiformis, all of these fibers together constitute the white, fiber-mass of 

 the capsula interna, met with in the horizontal section shown in Fig. 160. 



The frontal section reproduced in Fig. 163 is intended to complete the 

 idea of these relations shown in the horizontal section. Situated very far 

 forward, it strikes, principally, the ganglia of the corpus striatum, and 

 likewise distinctly shows the fibers of the capsula interna separating them. 



The form and location of the nucleus caudatus will probably be clear 

 to you now; but it will be more difficult to form an idea of the peculiar, 

 wedge-shaped figure of the nucleus lentiformis. A study of the horizontal 

 section and of the frontal section (Fig. 1C2) will be of benefit in this con- 

 nection. Internally, two other, somewhat lighter-gray, ganglionic masses 

 are associated with this ganglion, which are intimately attached to it by 

 fibers. We commonly speak, therefore, of a threefold division of the lenticu- 

 lar nucleus, whereas the broad, darker, outer division alone, the putamen, 

 probably is morphologically equivalent to the nucleus caudatus. This 

 nucleus caudatus sends its fibers, as Wcis mentioned above, through the an- 

 terior limb, or segment, of the internal capsule to the two inner divisions of 

 the lenticular nucleus, and on through them farther downward. The 

 fibers of the putamen run an exactly similar course. 



External to the corpus striatum lies the cortex of the island of Eeil. 

 In the narrow strip of white substance which lies between the cortex and 

 the ganglion, the capsula externa, there is situated an accumulation of 

 ganglionic cells, known a_s the claustrum. Anatomically, this is somewhat 

 different from the neighboring cortex, and it extends ventrally as far as into 

 the olfactory field. 



Behind the nucleus caudatus, the horizontal section shown in Fig. 160 

 passes through the thalamus, the interbrain. In front of this the pillars of 

 the fornix ascend from below. The commissura media, a thin band of gray 

 matter, extends from one thalamus to the other. External to the thalamus 

 lies the posterior liriib of the interned capsule. The point where both limbs 



