CHAP. XVIII.] THE NERVOUS SYSTEM. 209 



muscles of mastication : it also supplies the tongue with a 

 special nerve (the lingual) of the sense of taste. 



The sixth or abducens nerve supplies the external rectus 

 muscle of the eye. 



The seventh or facial nerve is the motor nerve of all the 

 muscles of expression in the face : it also supplies some muscles 

 of the neck and ear. It arises close to the sixth nerve on the 

 floor of the fourth ventricle. 



The eighth or auditory nerve is the special nerve of the sense 

 of hearing, being distributed exclusively to the internal ear. 



The ninth or glosso-pharyngeal nerve is distributed, as its 

 name indicates, to the tongue and pharynx, being the nerve of 

 sensation to the mucous membrane of the pharynx, of motion 

 to the pharyngeal muscles, and the special nerve of taste to part 

 of the tongue. 



The tenth or pneumogastric nerve has a more extensive dis- 

 tribution than any of the other cranial nerves, passing through 

 the neck and thorax to the upper part of the abdomen. It 

 contains both motor and sensory fibres. It supplies the organs 

 of voice and respiration with motor and sensitive filaments; 

 and the pharynx, oasophagus, stomach, and heart with motor 

 fibres. This nerve is sometimes spoken of as the par vagus. 



The eleventh or spinal-accessory nerve consists of two parts : 

 one, the spinal portion, and the other, the accessory portion to 

 the tenth nerve. It is a motor nerve supplying certain muscles 

 of the neck. It differs from the other cranial nerves in arising 

 from the spinal cord, but it leaves the skull by the same aper- 

 ture as the pneumogastric and glosso-pharyngeal. 



The twelfth or hypoglossal nerve is the motor nerve of the 

 tongue. 



All the cranial nerves, with the exception of the two first 

 pairs and the spinal accessory, arise from the gray matter in the 

 medulla oblongata, and any injury to the medulla oblongata is 

 attended with the most serious results, while extensive injury 

 arrests the respiratory processes and causes instant death. 



It will be observed that of the twelve pairs of cranial nerves, 

 four, arid a part of a fifth, are distributed to the eye ; viz. the optic, 

 motor oculi, pathetic, abducens, and the ophthalmic branch of 

 the fifth. The ear has one special nerve, the auditory, and is 

 sparingly supplied with motor and sensitive fibres from other 



