614 



CRANIAL NERVES. 



NINTH, OR HYPOGLOSSAL NERVE. 



The Ninth, or Hypoglossal Nerve, is the motor nerve of the tongue. It arises 

 by several filaments, from ten to fifteen in number, from the groove between 

 the pyramidal and olivary bodies, in a continuous line with the anterior roots 

 of the spinal nerves. According to Stilling, these roots may be traced to a 

 gray nucleus in the floor of the medulla oblongata, between the posterior 

 median furrow and the nuclei of the glosso-pharyngeal and vagus nerves. The 

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

 mater separately, opposite the anterior condyloid foramen, and unite together 

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



Fig. 343. Hypoglossal Nerve, Cervical Plexus, and their Branche.s. 



foramen in the occipital bone is double, these two portions of the nerve are sepa- 

 rated by a small piece of bone, which divides the foramen. The nerve descends 

 almost vertically to a point corresponding with the angle of the jaw. It is at 

 first deeply seated beneath the internal carotid and internal jugular vein, and 

 intimately connected with the pneumogastric nerve; it then passes forwards 

 between the vein and artery, arid at a lower part of the neck becomes super- 

 ficial below the Digastric muscle. The nerve then loops round the occipital 

 artery, and crosses the external carotid below the tendon of the Digastric 

 muscle. It passes beneath the Mylo-hyoid muscle, lying between it and the 

 Hyo-glossus, and is connected at the anterior border of the latter muscle with 

 the gustatory nerve ; it is then continued forwards into the Genio-hyo-glossus 

 muscle as far as the tip of the tongue, distributing branches to its substance. 



