94 



ESSENTIALS OF PHYSIOLOGY. 



The lateral aspect of the internal capsule is bounded by the 

 lenticular nucleus of the cerebral hemisphere. The anterior limb is 

 bounded on its mesial aspect by the head of the caudate nucleus of 

 the hemisphere. The anterior limb of the internal capsule contains 

 the fronto-pontine fibres. The genu and the anterior two-thirds of the 

 posterior limb contain the pyramidal fibres for the head, arm, trunk, and 



leg in the order mentioned from 

 before backwards. Behind the 

 pyramidal fibres are in order the 

 fillet, the auditory radiation, the 

 temporo-pontine fibres, and the 

 optic radiation (fig. 27). 



THE PATHS BETWEEN THE 

 CEREBRAL HEMISPHERES 

 AND THE SPINAL CORD. 



Afferent impulses enter the 

 spinal cord by the posterior nerve 

 roots. Those for muscle sense 

 and tactile discrimination travel 

 by the posterior column to the 

 nucleus gracilis and nucleus 

 cuneatus in the medulla oblon- 

 gata. From these nuclei fibres 

 arise and cross to the opposite 

 side, where they enter into the 

 formation of the fillet. The fillet 



passes through the pons and 

 FIG. 27. Diagrammatic representation of . . 



the internal capsule, as seen in hori- nnd-bram and internal capsule 



zontal section. (Cunningham.) From to terminate in the thalanius, 



Starling's Principles of Physiology. . , . , J _. 



from which the impulses are con- 

 veyed to the cortex of the cerebral hemisphere by the thalarno-cortical 

 fibres (fig. 28). The paths for tactile localisation, pain, heat, and cold 

 cross in the spinal cord very shortly above the entrance of the posterior 

 roots by which they were conveyed. They travel up by the spino- 

 thalamic tract, or possibly by short segmental tracts, to the medulla 

 oblongata, and there join the fillet, their subsequent course being that 

 just described. NV 



The pyramidal (cerebro-spinal) fibres take origin as the axons of 

 the Betz^ cells in the motor area, pass throughXthe white matter of the 

 cerebral hemisphere, through the internal capsule, the crusta of the 

 mid-brain, and the pons to become the pyramid of the medulla 



