224 HEAD AND NECK 



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 hypoglossal canal 

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

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

 orifice 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. 221). In the carotid triangle, it hoefe 

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

 mastoid branch, and, turning forwards, it crosses superficial to 

 the occipital, the internal and external carotid arteries and the 

 loop of the lingual artery. Then it passes across 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 root of the tongue. 



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

 nerve is connected 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 

 by one or more branches (p. 195). 



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 glosso-palatinus. 



Dissection. In the preceding dissections of the neck the 

 greater part of the cervical sympathetic, and the branches which 



