THE INTERNAL CAPSULE 



533 



fibres of this tract really start in, and depend for their 

 nutrition upon, the cells of the cortex of the cerebral 

 hemispheres. But this dependence is not extended to 

 the cells of the cortex generally ; on the contrary it is 

 limited to the cells of those parts of the cortex to which 

 we applied the expression " motor areas," in the preceding 

 section. Hence the pyramidal tract degenerates when 



Fio. 172. — Diagram ot the Coirse of the Cros-sed Pyramidal Tract 

 FROM THE (Motor) Cerebral Cortex to thf. Spinal Cord. 



C.C. corpus callosum : O.T. optic thalamus; C.S. corpus striatum; 

 Int. Cap. internal capsule ; Cb, cerebellum ; D. P. decussation i.f the 

 pyramids; Cr.p., Cr.p. crossed pyramidal tracts (see Fig. 156); S}}.C. 

 spinal cord. 



the cells of the " motor " areas are destroyed, and thus we 

 come to regard tlie pyramidal tract as the path bj' which 

 the (motor) impulses developed in the cortex are dis- 

 tributed to the cells of the spinal cord as a preliminary to 

 tlieir exit from the cord along the anterior roots of the 

 spinal nerves. We traced the pyramidal tract into the 

 bulb, and now we may, in conclusion, follow its further 

 cour.sc until its fibres make connection with the cerebral 

 cortex. 



