OP THE NERVOUS SYSTEM IN GENERAL. 475 



augments that of the nerves. In the adult man, the encepha- 

 lon, and more precisely the mesocephalon, that is to say, the 

 cranial extremity of the spinal marrow, the place from which 

 spring the crura cerebri and cerebelli, is truly the centre of 

 the action of the nervous system. 



759. What relation exists between the two substances of 

 the nervous system, and what is their particular use? 



Gall regards the gray substance as the matrix of the nerves, 

 as a fertile layer in which the nerves take root, and on which 

 depends their nutrition and growth. If Gall means by this 

 that there is a true production or vegetation, he is wrong: for 

 on the one hand no part is the product of another, all are de- 

 posited by the vessels, each one in its place; and on the other 

 hand, the white substance appears before the gray, both in the 

 animal kingdom and in the embryo. If he wishes to speak 

 only of an insertion, he was right. We ought to regard with 

 Ludwig, Gall, Carus, and Tiedemann, the gray substance as a 

 centre of activity, as fortifying the action of the white parts 

 which are implanted therein, in so much especially as it pro- 

 duces this effect by the great quantity of arterial blood which 

 traverses it. This substance abounds in the spinal narrow, 

 where the largest nerves are attached; it abounds equally in 

 the corpus rhomboideum of the cerebellum, and in the optic 

 thalami and corpora striata of the brain, as well as at the sur- 

 face of these two organs in man. 



760. What is the particular function of each part of the 

 nervous system ? 



The nerves (sect, ii.) conduct the impressions of the sur- 

 faces to the centre, and the principle of motion from the centre 

 to the muscles and vessels. 



The ganglions (sect, iii.), in consequence of the quantity of 

 blood which is distributed to them, and by that of their parti- 

 cular texture, modify the nervous action. 



The central nervous mass fulfils the most important parts 

 of innervation; it is the instrument of intelligence. 



The actions of combination, intermediate between sensation 

 and volition, are also functions of the encephalon. 



Instinct equally intermediate between these two orders of 



