316 HEAD AND NECK 



its construction, and one or more minute ganglia are 

 developed in connection with it. Its terminal twigs are given 

 to the muscles and mucous membrane of the pharynx, and 

 one branch (the ramus lingualis vagi) connects the plexus 

 with the hypoglossal nerve. 



Nervus Hypoglossus. The hypoglossal nerve makes its 

 exit from the cranium through the canalis hypoglossi 

 (O.T. anterior condyloid foramen). It pierces the dura mater 

 in two separate parts, which unite into one stem at the exit 

 of the bony canal. As it issues from the canal it lies deeply, 

 medial to the internal jugular vein and the internal carotid 

 artery; immediately afterwards it inclines laterally, and, 

 taking a half spiral turn around the ganglion nodosum of the 

 vagus, it appears between the two vessels, and descends between 

 them to the lower border of the posterior belly of the digastric 

 muscle, where it passes into the carotid triangle. Its close 

 connection with the ganglion nodosum of the vagus has 

 been noted already (p. 314). In the carotid triangle it hooks 

 round the lower end of the occipital artery, below its sterno- 

 mastoid branch, and, turning anteriorly, it crosses the occipital, 

 the internal and external carotid arteries and the loop of the 

 lingual artery superficially. Then it passes on the medial 

 sides of the posterior belly of the digastric and the stylo-hyoid, 

 and enters the digastric triangle, where it disappears medial 

 to the mylo-hyoid, and at the anterior border of the hyoglossus 

 it enters the base of the tongue. 



Branches of Communication. Near the base of the skull the hypoglossal 

 is brought into connection with (i) the superior cervical ganglion ; (2) the 

 vagus; and (3) the first cervical nerve; as it turns round the occipital 

 artery it receives (4) the ramus lingualis vagi from the pharyngeal plexus ; 

 and on the surface of the hyoglossus it communicates with (5) the lingual 

 nerve (p. 290). 



Branches of Distribution. (i) The meningeal branch arises 

 in the upper part of the canalis hypoglossi, and, regaining the 

 interior of the cranium, it is distributed to the dura mater 

 around the foramen magnum. (2) Vascular twigs are said to 

 be supplied to the deep aspect of the internal jugular vein. 

 (3) The descendens hypoglossi, which conveys fibres of the 

 first cervical nerve to the infra-hyoid muscles. (4) The nerve 

 to the thyreo-hyoid, which also consists of first cervical nerve 

 fibres. (5) The terminal branches, which supply the genio- 

 hyoid and all the intrinsic and extrinsic muscles of the tongue, 

 except the palato-glossus. 



