THE TWELFTH OR HYPOGLOSSAL NERVE 



1013 



divided and the border of the muscle defined, the nerve is to be sought for as it emerges from 

 the muscle to cross the occipital triangle. When found, it is to be traced upward through the 

 muscle, and a portion of it is excised above the point where it gives off its branches to the Sterno- 

 mastoid. In this operation one of the descending branches of the superficial cervical plexus is 

 liable to be mistaken for the nerve. 



THE TWELFTH OR HYPOGLOSSAL NERVE (N. HYPOGLOSSUS) 



(Figs. 747, 748). 



The twelfth or hypoglossal nerve is the motor nerve of the tongue. Its super- 

 ficial origin is by several filaments, from ten to fifteen in number, from the groove 

 between the pyramidal and olivary bodies of the medulla oblongata, in a continuous 

 line with the ventral roots of the spinal nerves. Its deep origin can be traced to a 

 nucleus of gray substance (nucleus hypoglossi] in the floor of the fourth ventricle, 

 described on page 880. 



To Durd mater 



To Ganglion on Trunk o/ Vagus 



'Branch from first Cervical 

 to Hypoglossal 



To Muscles 



of Tongue 



To Lingual Nerve 

 To Qeniohyoid 

 To Thyrohyoid 



To Anterior Belly oj Omohyoid 



* To Sternohyoid 

 To Sternothyroid 



ss 



To Posterior Belly of Omphyoid 



Fie. 747. Plan of the hypoglossal nerve. 



The filaments of this nerve are collected into two bundles, which perforate the 

 dura separately, opposite the anterior condylar foramen, and unite together 

 after their passage through it. In those cases in which the anterior condylar 

 or hypoglossal foramen in the occipital bone is double, these two portions of the 

 nerve are separated by the small piece of bone which divides the foramen. The 

 nerve descends almost vertically to a point corresponding with the angle of the 

 mandible. It is at first deeply seated beneath the internal carotid artery and internal 

 jugular vein, and is intimately connected with the vagus nerve (Fig. 748); it then 



