18 LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



The outer portion is called the nucleus lentiformis, and the inner 

 the nucleus caudatus. The mass of fibres between them has 

 received the name of internal capsule. This division of the 

 corpus striatum is plainly to be seen in an embryo of four 

 months, but its connection with the cortex of the hemisphere 

 has already disappeared, and the nucleus lentiformis and nucleus 

 caudatus appear as independent gray bodies. (See Fig. 9.) 



The corpus striatum lies along the whole floor of the 

 hemispheres. At its caudal end, however, it is very narrow, 

 and only the inner portion is demonstrable at all points. This 

 appears in all the cross-sections of the cerebrum as the tail of 

 the nucleus caudatus. The outer portion, the nucleus lenti- 

 formis, is much shorter. As you see, the nucleus caudatus pro- 

 jects free and clear into the ventricle. The nucleus lentiformis 

 also does at first. In later embryonic life, however, the narrow 

 fissure between it and the hemisphere-wall becomes so small that 

 it is no longer demonstrable. But we can always, even in adult 

 life, separate the hemisphere-walls from the outer surface of the 

 nucleus lentiformis without tearing any fibres. In the adult 

 brain the situation of the former fissure is of importance, for 

 here cerebral haemorrhages easily occur, and the mass of effused 

 blood, if it be not too great, fills up the space between the 

 hemisphere-wall and the outer division of the lenticular nucleus. 



The peripheral nerves appear very early. According to 

 the extremely important discoveries of His, there are two methods 

 of origin for the two kinds of fibres. All motor fibres arise as 

 axis-cylinder processes from cells situated in the ventral portion 

 of the medullary tube. Each cell sends out a fibre which passes 

 to the surface, and there unites with neighboring fibrils, to form 

 a ventral nerve-root. The sensory fibres, which, as a rule, 

 emanate from the dorsal region, have an entirely different origin. 

 They arise not in the central organ, but outside of it, in the 

 ganglia w r hich lie opposite it along its whole course. The cells 

 of these ganglia (spinal ganglia and ganglia of the cranial 

 nerves) send out fibres in two opposite directions. One of these 



