618 THE BRAIN. 



(or, as it is called, sagittal) section (Fig. 145) we find that the fibres form- 

 ing the strand in question do not continue parallel to each other as they rise 

 dorsally but diverge in a radiating manner, forming the so-called corona 

 rndiata. If again we take horizontal sections at proper levels (Figs. 138, 

 144), \ve find that this strand or rather thick band of dorsally directed radi- 

 ating fibres not only stretches ( Cip] between the thalamus and the gray mass 

 just spoken of, but reaching further forward passes (Cia) between the same 

 gray mass on the lateral side and another gray mass (Nc) on the median side, 

 the latter from its position being evidently the part of the corpus striatum 

 which projects into the lateral ventricle. The same horizontal sections further 

 teach us that the front part of the band (CVV) is bent at an angle upon the 

 hind part (Oip). 



It appears, then, from these sections that the fibres of the pes as they rise 

 up dorsally into the hemisphere spread out in the form of a fan bent upon 

 itself. This fan-like expansion of the pes is called the internal capsule, the 

 angle formed by the bend being called its genu or knee (C%), the part in 

 front of the knee the front limb, and the part behind the knee the hind limb. 

 And horizontal sections at levels more dorsal than those given in Figs. 138- 

 144 would show that the fibres composing this fan-like internal capsule, as 

 they rose dorsally, curved away in various directions to reach nearly all parts 

 of the surface of the hemisphere. We may add that though the internal 

 capsule is mainly composed of fibres which thus stretch all the way from the 

 cerebral cortex to the pes of the crus, it also contains other fibres of which 

 we shall speak later on. 



540. The gray mass separated from the thalamus by the hind limb of 

 the internal capsule is called as a whole the nucleus lenticularis, since in hori- 

 zontal section it presents a certain though distant resemblance to a lens. Of 

 the three divisions into which it is split up by the partitions of white matter, 

 the two median ones Gp ', Gp", are spoken of together as the globus pallidus, 

 the name being given to them on account of their paler color. The third, 

 lateral division Pt, is called the putamen. The use of these two names for 

 the two different parts of the one body, appears to be justified by the different 

 connections and features of the two parts. 



The gray mass which in a horizontal section (Fig. 138, JVb) is separated 

 from the nucleus lenticularis by the front limb of the external capsule, and 

 which projects into the lateral ventricle, is called the nucleus caudatus. The 

 nucleus caudatus and the nucleus lenticularis form together the corpus stria- 

 tum ; the former, since it projects into the lateral ventricle, being the part of 

 the corpus striatum seen when the lateral ventricle is laid open, is sometimes 

 spoken of as the intra-ventricular portion of the whole body, while the 

 nucleus lenticularis, which is wholly hidden in the hemisphere and in no 

 part projects into the lateral ventricle, is called the extra-ventricular por- 

 tion. 



But only a part, indeed only a relatively small part, of the nucleus cauda- 

 tus is disclosed in such a horizontal section ; to learn the somewhat peculiar 

 form and relations of the whole nucleus a number of sections of a hemi- 

 sphere taken in different planes must be studied ; and these will at the same 

 time explain why the nucleus is called " caudatus." These teach us that the 

 nucleus has somewhat the form of a comma (Fig. 142). The thick, rounded 

 head forms the lateral wall of the front part of the lateral ventricle ; thence 

 the body passes backward, narrowing rapidly and diverging somewhat later- 

 ally ; in its course it arches over the nucleus lenticularis, curving so much 

 that the end of the tail, sweeping round the hinder border of that body and 

 changing its direction, runs eventually ventral to it. In a horizontal section 

 taken at a certain depth, such as that represented in Fig. 138, only a portion 



