974 INTERNAL CAPSULE. [BOOK HI. 



missure. In. the insula or island of Keil. Iv. the lateral ventricle; L v. d. 

 descending horn of lateral ventricle; V. 3. in the position of the third 

 ventricle ; the outlines of the cavities are made diagrammatically distinct by 

 thick black lines. Op. optic tract; P, P. Parietal lobe. T. Temporal lobe. 



fibres not only stretches (dp) between the thalamus and the grey 

 mass just spoken of, but reaching farther forward passes (Gia) 

 between the same grey mass on the lateral side and another grey 

 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 (Cia) 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, (Gig} 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. 115 121 would shew 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. 



627. The grey mass separated from the thalamus by the 

 hind limb of the internal capsule is called as a whole the nucleus 

 lenticularis, since in horizontal 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 Up', Gp" are spoken of together as the globus pallidus, the 

 name being given to them on account of their paler colour. 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 grey mass which in a horizontal section (Fig. 115, Nc) 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 striatum ; 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 intraventricular portion of the whole body, while 

 the nucleus lenticularis, which is wholly hiden in the hemisphere 

 and in no part projects into the lateral ventricle, is called the 

 extraventricular portion. 



