GREAT VESSELS AND NERVES OF NECK 221 



to them. Its posterior relations, therefore, are similar to 

 those of the common and internal carotid arteries (pp. 117, 

 211). At the root of the neck it enters the thorax, and has 

 different relations on the two sides. On the right side it 

 crosses the first part of the subclavian artery ; on the left side, 

 after crossing anterior to the thoracic duct, it proceeds down- 

 wards between the left common carotid and subclavian 

 arteries, posterior to the left innominate vein. For its 

 thoracic relations see Vol. II. p. 127. 



The vagus, like the glosso-pharyngeal, has two ganglia in 

 connection with its upper part. These are the ganglion 

 jugulare and the ganglion nodosum. 



Ganglion Jugulare (O.T. Ganglion of Root). The jugular ganglion is 

 situated within the jugular foramen. It is a rounded swelling which is 

 connected by communicating twigs with several of the nerves in the 

 neighbourhood, and it gives off two branches of distribution. 



Branches of Communication. (i) With the facial nerve; (2) with the 

 petrous ganglion of the glosso-pharyngeal ; (3) with the accessory ; (4) with 

 the superior ganglion of the sympathetic. 



Branches of Distribution. (i) Meningeal ; (2) Auricular nerve. 



The meningeal branch is a minute twig which runs upwards through 

 the jugular foramen, and, dividing into two branches, is distributed to 

 the dura mater in the posterior cranial fossa. 



The auricular nerve (O.T. Arnold's nerve) obtains a filament of com- 

 munication from the petrous ganglion of the glosso-pharyngeal, and passes 

 backwards, upon the lateral surface of the bulb of the internal jugular vein, 

 to enter a minute aperture on the posterior part of the lateral wall of the 

 jugular fossa. A narrow canal then conducts it through the substance 

 of the temporal bone, and, on its way, it crosses the canalis facialis a 

 short distance above the stylo-mastoid foramen. It is thus brought into 

 close relation with the facial nerve and is connected with it by an 

 ascending and a descending branch of communication. Finally, it appears 

 on the surface of the skull, in the interval between the mastoid process and 

 the external acoustic meatus, where it communicates with the posterior 

 auricular branch of the faciaL It supplies the skin on the posterior aspect 

 of the outer surface of the wall of the meatus, the skin covering the lower 

 half of the inner surface of the wall of the meatus, and the lower half of 

 the tympanic membrane. 



Ganglion Nodosum. After emerging from the jugular 

 foramen, the vagus nerve is joined by the cerebral portion of 

 the accessory nerve, and swells out into the ganglion nodosum 

 (O.T. ganglion of trunk). 



The ganglion nodosum is an elongated reddish-coloured 

 swelling, about 18 mm. (three-quarters of an inch) in length, 

 which is developed upon the stem of the vagus, 12.5 mm. 

 (half an inch) below the base of the cranium. Strong 

 branches of communication pass between it and the first 



