544 



CRANIAL NERVES. 



NINTH OR IIYPOGLOSSAL 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. The nerve descends almost vertically to a point corresponding with 



Fig. 279. Hypoglossal Nerve, Cervical Plexus, and their Brandies. 



the atfgle 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, and, descending the neck, 

 becomes superficial 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 

 Hyoglossus, 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. 



