THE TWELFTH OR HYPOGLOSSAL NERVE. 



825 



condyloid foramen it gives off, according to Luschka, several filaments (recurrent) 

 to the dura mater in the posterior fossa of the base base of the skull. 



The descendens hypoglossi is a long slender branch which quits the hypoglossal 

 where it turns round the occipital artery. It descends obliquely across the sheath 

 of the carotid vessels, and joins the communicating branches from the second and 

 third cervical nerves, just below the middle of the neck, to form a loop. From the 

 convexity of this loop branches pass forward to supply the Sterno-hyoid, Sterno- 

 thyroid, and both bellies of the Omo-hyoid. According to Arnold, another filament 

 descends in front of the vessels into the chest and joins the cardiac and phrenic 

 nerves. The descendens hypoglossi is occasionally contained in the sheath of the 

 carotid vessels, being sometimes placed over, and sometimes beneath, the internal 



'*\ , Hypo-glossal nen-e. 



PHtniinogastric nerve. 



FIG. 4W. Hypoglossal nerve, cervical plexus, and their branches. 



jugular vein. The fibres of this nerve are chiefly derived from the first and 

 second cervical nerves by means of the filaments of communication already men- 

 tioned. 



The thyro-hyoid is a small branch arising from the hypoglossal near the poste- 

 rior border of the Hyo-glossus ; it passes obliquely across the great cornu of the 

 hyoid bone and supplies the Thyro-hyoid muscle. 



The muscular branches are distributed to the Stylo-glossus, Hyo-glossus, Genio- 

 hyoid. and Genio-hyo-glossus muscles. At the under surface of the tongue numer- 

 ous slender branches pass upward into the substance of the organ to supply its 

 muscular structure. 



Surgical Anatomy. The hypoglossal nerve is an important guide in the operation of liga- 

 ture of the lingual artery (see page 553). 



