530 



PHYSIOLOGY 



CHAP. 



The nuclei of the corpus striatum are connected by nerve- 

 fibres ; other fibres run to adjacent parts of the internal capsule, 

 to the corona radiata and to the cortex. 



The .internal capsule is the mass of white fibres situated 

 between the lenticular nucleus, caudate nucleus, and the optic 

 thalamus (Fig. 263). In front, behind, and above it is continuous 



with the white matter of 

 the hemispheres, and is 

 composed of fibres that 

 spread out like a fan 

 whence the name corona 

 radiata. Below, the fibres 

 of the internal capsule and 

 corona radiata are con- 

 tinuous with the pes of the 

 cerebral peduncle. In hori- 

 zontal sections, as in Fig. 

 263, the internal capsule 

 presents a knee, the anterior 

 and posterior segments join- 

 ing at an angle of about 

 120. Clinical observations 

 have led to the conclusion 

 that the fibres running in 

 the middle third of the 

 internal capsule, i.e. those 

 along the globus pallidus 

 of the lenticular nucleus, 

 are in connection with the 

 part of the cerebral cortex 

 which we know as the motor 

 area; those of the anterior 

 tliird with the prefrontal 

 region; and those of the 

 posterior third with the 

 temporo-occipital regions of 

 the cortex. 



The localisation in the 

 internal capsule of the fibres 

 from the nuclei of the corpus striatum, the optic thalamus, the 

 subthalamic region, and the cortex of the opposite hemisphere, 

 through the great interhemispherical commissure of the corpus 

 callosum, is not exactly known. 



The cerebral mantle in the higher vertebrates, particularly in 

 man, comprises the greater part of the mass of the cerebral 

 hemispheres ; it is divided by the sulcus longitudinalis and united 

 by the corpus callosum. 



FIG. 263. Horizontal section through part of cerebral 

 hemisphere. (Schafer, after Shattock.) Natural 

 size. The section is viewed from below ; v.1., lateral 

 ventricle, anterior horn ; c.c., corpus callosum ; 

 s.L, septum lucidum ; a./., anterior pillars of fornix ; 

 vS, third ventricle; th, optic thalamus; st, stria 

 terminalis ; c, nucleus caudatus, and n.l., nucleus 

 lenticularis of corpus striatum; i.e., internal capsule; 

 g, its knee or genu ; n.c., tail of nucleus caudatus 

 appearing in descending horn of lateral ventricle ; 

 cl, claustrum ; /, islaud of Reil. 



