296 THE NERVOUS SYSTEM 



glossus, hyoglossus, genio-hyoid and genio-hyoglossus mus- 

 cles. 



Functions. This nerve posseses no sensibility at its root, 

 but receives sensory fibers from anastomoses with other 

 nerves. Its stimulation, therefore, causes movements of the 

 tongue and some pain. Section of both nerves causes difficult 

 deglutition, loss of power over the tongue and consequent 

 disturbances in mastication and articulation. When the 

 twelfth is affected in hemiplegia the tongue, on protrusion, 

 deviates to the affected side because it is pushed out by the 

 genio-hyoglossus. 



It will be seen from the foregoing that, classified accord- 

 ing to their properties at their roots, the L, II. and VIII. 

 are nerves of special sense ; the III., IV., VI., XI and XII. 

 are motor; the X. is sensory; and the V., VII. and IX. are 

 mixed. It is to be remembered, however, that most of these 

 (excepting the nerves of special sense) are mixed in their 

 distribution by reason of the reception of fibers from other 

 nerves. The term "mixed" in the above classification is used 

 as meaning the association of special sensory fibers with 

 motor or common sensory fibers as well as the associa- 

 tion of these latter with each other. The VII. is classed as 

 a mixed nerve only by allowing the intermediary nerve of 

 Wrisberg is to be considered a part of it. Its own proper 

 root is purely motor. 



THE SPINAL NERVES. 



The spinal nerves, thirty-one on each side, are so called 

 from the fact that they originate in the spinal cord and es- 

 cape from the spinal canal by the intervertebral foramina. 

 Eight pairs come from the cervical region of the column, 

 twelve from the dorsal, five from the lumbar, five from the 

 sacral, and one from the coccygeal. They are numbered ac- 

 cording to their foramina of exit. 



Each nerve rises by two roots an anterior which can be 



