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C. JUDSON HERRICK 



the pyramidal tract fibers descend through the human spinal 

 cord for the most part in the dorso -lateral columns, not in the 

 ventral columns like most other motor tracts. In most lower 

 mammals the pyramidal tract actually descends within the 

 dorsal funiculus in the closest possible association with the 

 peripheral sensory fibers, and this arrangement is clearly the 

 primitive relation of the descending cortical pathway. 



shin 



muscle 



Figure 4. Diagram of the relations of the pyramidal tract in a rabbit or similar 

 lower mammalian brain. Sensory stimuli enter the spinal cord from the skin 

 through the peripheral sensory neurone, S, and ascend to the cerebral cortex 

 through the lemniscus, L. The descending pyramidal tract, P, lies in the 

 dorsal funiculus of the spinal cord. Its intercalary neurone, /, may be stim- 

 ulated by both the peripheral neurone S and by the pyramidal tract P. It 

 discharges upon the peripheral motor neurone, M . 



Accordingly, stimulation of the skin of the body excites a 

 dorsal spinal root fiber which ascends toward the cortex within 

 the spinal cord and also gives collateral branches to intercalary 

 neurones of the spinal cord itself. The latter neurones may 

 excite motor elements of the spinal cord to an immediate reflex 

 response which is well under way before the cortical return 

 motor impulse gets back to the spinal cord and discharges into 

 these same intercalary neurones which are already under sen- 



