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A MANUAL OF PHYSIOLOGY 



The Internal Capsule. We have already recognised the 

 pyramidal tract and the afferent tegmental path as con- 

 stituents of the internal capsule. The cranial fibres of the 

 pyramidal tract occupy the genu or knee, the spinal fibres 

 the anterior two-thirds of the posterior limb. The posterior 

 third of the posterior limb contains the sensory path.* 



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 



FIG. 250 DIAGRAMMATIC HORIZONTAL SECTION OF LEFT HALF OF BRAIN 

 TO SHOW INTERNAL CAPSULE. 



and temporal portions of the cerebral cortex. The first 



passes through its anterior limb, the second behind the 



ensory path in its posterior limb. The cells of origin of 



f The common statement that the efferent (motor) path occupies the 

 anterior two-thirds, and the afferent (sensory) path the posterior third of 

 the posterior limb of the internal capsule, while no doubt true in a general 

 sense, is not strictly correct. Some motor fibres seem to be intermingled 

 with the sensory in the posterior third, for lesions of this region produce 

 a certain degree of paralysis as well as anaesthesia on the opposite side 

 of the body. A pure capsularhemianaesthesia, that is, a loss of sensation 

 on the opposite side due to a lesion in the internal capsule and unaccom- 

 panied by motor defect, does not appear to exist. 



