ANATOMY OF THE NERVOUS SYSTEM 131 



thirds of the tongue, the lower teeth, the salivary glands, and 

 the muscles which move the lower jaw in mastication. 



The sixth pair of cranial nerves VI, or abducentes arises from 

 the posterior margin of the pons Varolii, and each is distributed 

 to one muscle of the eyeball. 



The seventh pair (facial nerves) , VII, appear also at the posterior 

 margin of the pons. They are distributed to most of the muscles 

 of the face and scalp. 



The eighth pair (auditory nerves), VIII, arise close to the facial. 

 They are the nerves of hearing and are distributed entirely to the 

 internal ear. 



The ninth pair (glossopharyngeals), IX, arising close to the 

 auditories, are distributed to the mucous membrane of the pharynx 

 the posterior part of the tongue, and the middle ear. 



The tenth pair (pneumogastric nerves or vagi), X, arise from the 

 sides of the medulla oblongata. Each gives branches to the 

 pharynx, gullet, and stomach, the larynx, windpipe, and lungs, 

 and to the heart. The vagus runs farther through the body than 

 any other cranial nerve. 



The eleventh pair (spinal accessory nerves), XI, do not arise 

 mainly from the brain but by a number of roots attached to the 

 lateral columns of the cervical portion of the spinal cord, be- 

 tween the ventral and dorsal roots of the proper cervical spinal 

 nerves. Each, however, runs into the skull cavity alongside of 

 the spinal cord and, getting a few filaments from the medulla 

 oblongata, passes out along with the glossopharyngeal and pneu- 

 mogastric nerves. Outside the skull it divides into two branches, 

 one of which joins the pneumogastric trunk, while the other is 

 distributed to muscles about the shoulder. 



The twelfth pair of cranial nerves (hypoglossa) , XII, arise from 

 the sides of the medulla oblongata; they are distributed mainly 

 to the muscles of the tongue and hyoid bone. 



It must be remembered that the cranial nerves, like the spinal 

 nerves, are really bundles containing hundreds of axons having 

 various destinations. Just as in the spinal nerve plexuses bundles 

 of axons cross over from one nerve-trunk to another, so in many 

 of the cranial nerves, especially the fifth and seventh, there 

 are branchings from one nerve to another, making it difficult to 

 tell in many cases from what part of the brain the nerves to a 



