882 



THE CENTRAL NERVOUS SYSTEM 



The destination of the afferent fibres of the internal capsule has 

 not been definitely settled. There is no doubt that they pass up to 

 the convolutions around the fissure of Rolando (central convolu- 

 tions), and there is reason to believe that some of them terminate in 

 the ' motor ' region in front of that fissure, although many of the 

 fibres concerned in tactile sensations seem to end in the ascending 

 parietal convolution. 



But we have not yet exhausted the constituents of the internal 



capsule. Two great cones of fibres 

 sweep down into it, one from the 

 frontal, the other from the occipital 

 and temporal portions of the cerebral 

 cortex. The first passes through its 

 anterior limb, the second behind the 

 sensory path in its posterior limb. 

 The cells of origin of the frontal fibres 

 are known, and those of the occipital 

 and temporal fibres are supposed, to 

 be situated in the cortex. They are 

 therefore efferent fibres as regards 

 the cortex (cortifugal). Running on 

 through the crusta of the cerebral 

 peduncle (Fig. 352), the frontal tract 



Fig. 358. Pyramidal Tract in In- 

 ternal Capsule (Simpson and 

 Jolly). Horizontal section 

 through right cerebral hemi- 

 sphere, cutting fibres of internal 

 capsule transversely at an upper 

 level a little below the upper 

 surface of the lenticular nucleus. 

 The extent of the degeneration 

 following destruction of the 

 whole of the right ' motor ' cor- 

 tex, except the ' head and eyes ' 

 area (in one of the lower mon- 

 keys), is shown. Note over- 

 lapping of fibres from face, arm, 

 and leg areas, as shown by ex- 

 periments in which one or other 

 of these areas was alone re- 

 moved. 



Fig- 359- Pyramidal Tract in Internal 

 Capsule at Lower Level (Simpson and 

 Jolly). CN, head of caudate nucleus; 

 OT, optic thalamus; Cl, claustrum. 



internal, the occipito-temporal external, they end in the grey 

 matter of the pons, and serve as one segment of an extensive 

 connection between the cerebral and the cerebellar cortex of the 

 opposite side, the other segment being formed by neurons whose 

 cell-bodies are situated in the pons, and whose axons, crossing 



