840 PHYSIOLOGY. 



pierces the sterno-mastoid to supply it and the trapezius. This por- 

 tion of the nerve communicates with several cervical nerves. 



Physiology. The eleventh nerve is generally considered to be 

 motor. Any observable sensibility must be due to anastomosis with 

 the cervical nerves. 



From experimentation it has been found that the accessory 

 branch presides, through motor branches in the vagus to the laryn- 

 geal muscles, over the formation of sound and its tone. The spinal 

 branch is concerned in the duration, intensity, and modulation of 

 the vocal sound. Hence it regulates the rhythm of speech and song. 



Aphonia is often due to hysteria, but may be due to lead-poison- 

 ing, syphilis, or to such reflex causes as intestinal worms. The reflex 

 that is established between the vocal and genital organs is also shown 

 by troubles in the spinal branch of the spinal accessory. The voice 

 may be lost at times during menstruation. 



TWELFTH PAIR, OR HYPOGLOSSAL NERVE. 



The nuclei of the hypoglossal nerve are under the floor of the 

 fourth ventricle, on each side of the raphe. Beneath the main 

 nucleus of the hypoglossal nerve is a collection of cells in the for- 

 matio reticularis, called the hypoglossal nucleus of Holler. 



Cortical Connection. The motor path is from the inferior part 

 of the central convolutions. 



Anastomoses, The connections of the hypoglossal are : 1. With 

 the superior cervical ganglion of the sympathetic, which supplies 

 vasomotor fibers to the vessels of the tongue. 2. The plexus gangli- 

 formis vagi gives a small lingual branch which supplies the tongue 

 with sensory fibers. 3. The hypoglossal is also connected with tho 

 upper cervical nerves. 



Physiology. The hypoglossus, by itself, is purely motor. It 

 moves the muscles of the tongue. When its original filaments are 

 torn out there is never any pain. Sensibility of its terminal branches 

 is due to anastomoses witlrthe lingual. When the hypoglossus is 

 cut, the tongue remains quiescent in the mouth. 



In unilateral paralysis of the hypoglossus the tongue, when pro- 

 truded, passes over to the paralyzed side. This phenomenon is occa- 

 sioned by the action of the genio-hyo-glossus of the sound side. 



LITERATURE CONSULTED. 



Gordinier, "Nervous System." 





