118 



LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



the following diagram of an innervation tract. Every peripheral 

 nerve at least, every motor nerve ends in the central organ 

 in a nucleus. Nerve-roots and the nucleus form the first part 

 of the tract. To the nucleus there pass fibres of the corona 

 radiata from the cortex of the hemispheres, and thus is formed 

 the second link in the chain ; nerve, nucleus corona radiata, 

 cortex. 



FIG. 68. 

 Diagram of an innervation tract from the cortex to a (motor) cranial nerve. 



Bahn in Stabkranz u. Capsula, Tract in corona radiata and capsule. 



Hinteres Langsbundel, Post, loiigitud. fasciculus. Kern, Nucleus. Periph. tfvrv, Peripheral nerve. 



Rinde, Cortex. 



So long as the first part of the tract is intact, the muscles 

 can be brought into action by electric, mechanical, or reflex irri- 

 tation, and, in animals, to a certain extent by the influence of 

 the will. If either nerve or nucleus is destroyed we have abso- 

 lute paralysis. In order, however, to obtain the full effect of a 

 conscious voluntary act, the second part of the tract must also 

 be intact ; this is particularly true of the highly-developed human 



