CHAPTER III. 



THE FUNCTIONS OF THE NERVES. - 



Inasmuch as I have already divided the nervous system into 

 three principal portions, namely,, the animal organs, sensorium 

 commune, and the nerves properly so called, I shall also divide 

 its functions into three classes, namely, into animal operations, 

 operations of the sensorium, and operations of the nerves. The 

 functions of the nerves are first to be considered; then the 

 operations of the common sensory, and lastly, the animal 

 operations. 



SECTION I. ON THE ACTION OF THE NERVES IN PRODUCING 



SENSATION AND MOTION. 



Since the nerves represent cords commencing in the cerebrum, 

 medulla oblongata, and medulla spinalis, and thence extended 

 throughout the whole body, two extremities are noted in each 

 nerve; of these, the one is internal and continuous with the 

 cerebrum, or medulla oblongata, or medulla spinalis, and termed 

 the origin or beginning of the nerve ; the other is external where 

 the nerves terminate in various parts of the body, and termed, 

 therefore, the end of the nerve. It is besides certain, that the 

 nerves have the property of most readily receiving impressions, 

 however great or of whatever kind they may be, and of trans- 

 mitting them when received with great rapidity along their 

 whole length. Consequently, if an impression be made at the 

 termination of a nerve, which is termed an external impression, 

 it is very rapidly transmitted along the whole length of the nerve 

 quite to its origin ; and vice versa, if the impression be made 

 at the commencement of the nerve, which is termed an internal 

 impression, it is transmitted with the same rapidity to the 

 termination of the nerve. But if the impression be made 

 midway on the trunk of the nerve, it is rapidly transmitted a 

 the same moment to both its origin and termination. This 



