PNEUMOGASTRIC NERVE 771 



runs downwards on the side of the trachea, jxjsterior to tiie riglit innominate vein 

 and the superior vena cava, to reach the posterior aspect of the right bronchus. 

 Behind the Ijronchus it expands into a great, flat, plexiforni band, from Avhich the 

 posterior puhnonarv^ plexus proceeds. The vagus then inclines inwards in the form 

 of two cords, and conmumicates with the pneumogastric of the oi)i)osite side both 

 in front and behind tlie o'sophagus to form the o'sophageal plexus (i)lexus guhe). 

 Having interchanged a considerable number of fi]>res with the other nerve, the right 

 vagus then descends (having regained the form of one nerve) behind the O'sophagus 

 through the (i^sophageal opening of the diai)hragm, and spreads out on the 

 posterior surface of the stomach. 



The left vagus nerve enters the thorax behind the left common carotid artery 

 between the latter and the left subclavian artery. As it approaches the arch of 

 the aorta it bends suddenly backwards, and crosses the root of the subclavian artery 

 on the left side of that vessel, immediately under cover of the pleura. It then 

 crosses the left side (in front) of the arch of the aorta, and bends backwards to 

 reach the; posterior aspect of the left l)ronchus, where it si)reads out in a similar 

 manner to the nerve of the right side. It then descends on the (esophagus, entering 

 into the plexus gula?, and on reaching the dia])ln"agm passes in the form of a single 

 trunk in front of the (psoi)hagus into the abdominal cavity, and spreads out on the 

 anterior surface of the stomach. 



At the base of the skull the vagus presents two ganglia: an upper ganglion, or 

 ganglion of the root ; and a loAver, or ganglion of the trunk. 



The ganglion of the root is placed within the jugular foramen opposite the 

 jugidar ganglion of the glosso-pharyngeal. It is an irregular greyish swelling of 

 from four to six millimetres in length. It is usually regarded as corresponding to 

 a sjjinal ganglion. 



The ganglion of the trunk, situated a little below the preceding, is a fusiform 

 enlargement of the nerve about twenty millimetres in length, and four to live milli- 

 metres in transverse diameter at its thickest part. The hypoglossal nerve isfirndy 

 attached to it by connective tissue and encloses it in a spiral turn, being placed at 

 tirst to the inner side of the vagus, then passing behind, then to its outer side, and 

 finally ca'ossing it in front. The superior cervical ganglion of the sj'mpathetic is 

 behind and a little external to the vagus; the glosso-pharyngeal is in front of it. 

 The accessory portion of the spinal accessory nerve joins the ganglion ofthetruidc; 

 some of the fil)res running over the ganglion into the pharyngeal and superior 

 laryngeal l)ranches. 



Branches. — The branches of the vagus may be classified into (1 ) connnunicating 

 ])ranchcs; and (2) ])ranch('S of distril)ution. 



(1) Communicating branches. — The vagus communicates with the following 

 nerves: — (a) the glosso-pharyngeal to the auricular branch of the pneumogastric; 

 (b) the spinal accessory; (c) the hypoglossal; (d) the sympathetic; and {e) the 

 upper two spinal nerves. 



(a) Besides the communicating branch to the vagus just referred to, a communi- 

 cating twig is given off from the pneumogastric, close to the base of the skull, 

 which joins the glosso-jtliaryngeal nerve immediately below the petrous ganglion. 



(6) The spinal accessory gives some fine filaments to the ganglion of the root 

 of the vagus within the jugular foramen. Lower down, the remainder of the 

 accessory portion joins the ganglicm of the trunk. 



(c) Tlie hypoglossal furnishes two or three fine filaments to the ganglion of the 

 trunk of the vagus. These fihunents are given off l)y the hypoglossal as it winds 

 round the ganglion. 



(d) Two or three twigs from the superior cervical ganglion of the sympa- 

 thetic join the ganglia of the trunk and root. Lower down the branches of distri- 

 bution of the vagus communicate extensively with the sympathetic. 



(e) A twig passes from the loop formed by the anterior primary divisions of 

 the up])er two spinal nerves to the ganglion of the trunk of the vagus. This com- 

 numication is not constant. 



(2) Branches of distribution. — These are («) the meningeal; (6) auricular; 

 {<•) pharyngeal; (r/) su])cri()r laryngeal; (e) inferior laryngeal; (/) cardiac; 

 (g) pulmonary; (/t) oesophageal; and (/) abdominal branches. 



