THE NERVOUS SYSTEM 2O/ 



the circulation. The medulla oblongata appears to be the 

 general receptacle of the impressions of the nerves of the 

 special senses, and the spinal cord that of general sensa- 

 tion. 



Functions of the Nerves. Of the spinal nerves and of 

 one of the cranial (trifacial), it may be stated that they 

 have two roots one for conveying motor and one for 

 carrying sensory impulses. In other words, one set for 

 the functions of motion and the other for those of sensa- 

 tion. 



No difference has been discovered in the structure of 

 the several kinds of nerves in any part of their course, and 

 the functions they are designed to perform can only be 

 learned by ascertaining the place of their origin. The 

 nerves may be divided into five groups, according to their 

 functions : 



1. Nerves of Special Sensation. There are the first, 

 second, eighth, and ninth pair of cranial nerves, and are 

 concerned with smelling, seeing, hearing, and tasting. 



2. Nerves of General Sensation. In those parts that 

 require sensation for safety and the performance of their 

 functions there is an abundant supply of sensitive nervous 

 filaments. The nerves of sensation are distributed chiefly 

 to the skin. Few filaments ramify in the mucous mem- 

 branes and muscles. The head is supplied with sensa- 

 tion by the ophthalmic and superior maxillary divisions 

 of the fifth cranial nerve; the remainder of the body 

 by fibers from the mixed spinal nerves. 



3. Nerves of Motion. To these belong the third, the 

 fourth, part of the fifth, the sixth, the seventh, the elev- 

 enth, and the twelfth pairs of cranial nerves. They are 

 distributed to the muscular fibers, and, by their action, 

 give rise to muscular contraction. (By referring to the 

 illustration, Fig. 114, the several nerves that control the 

 general system may be seen.) 



