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A MANUAL OF PHYSIOLOGY 



The Internal Capsule. We have already recognised the 

 pyramidal tract and the afferent tegmental path as constituents 

 of the internal capsule. The cranial fibres of the pyramidal tract 

 occupy mainly the genu or knee, the spinal fibres the posterior 

 limb as far back as the posterior border of the lenticular nucleus. 

 The fibres from the various motor areas are to a certain extent 



arranged in order in the cap- 

 sule, those for the eyes and 

 head lying farthest forward, 

 those for the leg farthest back, 

 while the fibres going to the 

 face, arm and trunk occupy 

 intermediate positions (Fig. 

 331). The separation, how- 

 ever, is far from complete, the 

 fibres of neighbouring regions 

 being considerably intermixed 

 (Hoche). As the tracts pass 

 downwards the intermingling 



FIG. 332. PYRAMIDAL TRACT IN 

 INTERNAL CAPSULE (SIMPSON 

 AND JOLLY). 



Horizontal section through right 

 cerebral hemisphere, cutting fibres 

 of internal capsule transversely at 

 an upper level a little below the 

 upper surface of the lenticular 

 nucleus. The extent of the de- 

 generation following destruction of 

 the whole of the right ' motor ' 

 cortex, except the ' head and eyes ' 

 area (in one of the lower monkeys), 

 is shown. Note overlapping of 

 fibres from face, arm, and leg areas, 

 as shown by experiments in which 

 one or other of these areas was alone 

 removed. 



FIG. 333. PYRAMIDAL TRACT IN INTER- 

 NAL CAPSULE AT LOWER LEVEL (SIMP- 

 SON AND JOLLY). 



CN, head of caudate nucleus ; O.T, 

 optic thalamus ; Cl, claustrum. 



becomes continually greater (Simpson and Jolly) (Figs. 332, 333) . 

 The afferent fibres from the thalamus to the cortex, which we 

 have described as the last segment of the afferent tegmental 

 path, lie in the posterior part of the posterior limb. But here 

 again there is no absolutely sharp line of demarcation. Some 

 motor fibres are intermingled with the sensory in the posterior 



