THE TENTH, VAGUS, OR PNEUMOGASTRIC NERVE G89 



The left vagus (Fig. 42S) enters the thorax on the ventral face of the oesophagus, 

 crosses obh(iuely under the left brachial artery, and passes back on the external 

 surface of that vessel in company with a large cardiac nerve.' Separating from 

 the latter, the vagus continues backward on the left face of the aorta, inclines to 

 the upper surface of the left bronchus, and divides into dorsal and ventral branches. 



The dorsal and ventral branches unite witli the cori'csponding branches of the 

 opposite nerve, thus forming dorsal and ventral oesophageal trunks (Truncus 

 oesophageus dorsalis, ventralis) . These run backward in the posterior mediastinum, 

 above and below the oesophagus respectively, and enter the abdominal cavity 

 through the hiatus oesophageus; they supply branches to the oesophagus and 

 anastomose with each other. The dorsal trunk receives the major part of its fibers 

 from the right vagus. After entering the abdomen it passes to the left of the 

 cardia, gives branches to the visceral surface of the stomach, and ends in the 

 coeliac and subsidiary plexuses. The ventral trunk passes to the lesser curva- 

 ture of the stomach and ramifies on the parietal surface of the stomach; it forms 

 here the anterior gastric plexus, from which l)ranches are supplied also to the first 

 part of the duodenum and to the liver. 



The collateral branches of the vagus are as follows: 



1. The pharyngeal branch (R. pharyngeus) is given off in relation to the supe- 

 rior cervical ganglion, turns around the internal carotid artery, and runs downward 

 and forward on the guttural pouch to the dorsal wall of the pharynx (Fig. 437). 

 Here its branches concur with the pharyngeal branch of the ninth nerve and with 

 filaments from the spinal accessory and the sympathetic in forming the pharyngeal 

 plexus. This supplies numerous twigs to the pharynx, and a larger branch which 

 passes along the side of the oesophagus and ramifies in its cervical part. 



According to EUenberger and Baum the pharyngeal plexus receives filaments also from the 

 digastric, superior lar^-ngeal, hypoglossal, and first cervical nerves. The branches of the plexus 

 form secondary intermuscular and submucous plexuses, in whicli there are numerous minute 

 ganglia. 



2. The superior or anterior laryngeal nerve (N. laryngeus cranialis) is larger 

 than the preceding and arises a little behind it (Fig. 437). It crosses the deep face 

 of the origin of the external carotid artery, runs downward and forward over the 

 lateral wall of the pharynx behind the hypoglossal nerve, and passes through the 

 foramen below the anterior cornu of the thyroid cartilage. Its terminal branches 

 ramify in'the mucous membrane of the larynx, the floor of the pharynx, and the 

 entrance to the oesophagus; they anastomose with those of the recurrent. At 

 its origin the nerve gives off its small external branch (H. externus); this descends 

 to the crico-thyroid muscle, which it supplies, and sends filaments to the crico- 

 pharyngeus also. It may arise from the trunk of the vagus or from the pharyngeal 

 branch. 



At the point of origin of the superior laryngeal nerve there is a plexiform widening which is 

 regarded by some authors as the homologue of the ganglion nodosum of man. From it a filament 

 arises which, after a short course, rejoins the vagus or enters the sympathetic trunk. Stimulation 

 of its central end causes a reduction of the blood-pressure, and it is therefore termed the depressor 

 nerve (N. depressor). 



3. The recurrent nerve (N. recurrens), also termed the inferior or posterior 

 laryngeal nerve, differs on the two sides in its point of origin and in the first part of 

 its course. The right nerve (Fig. 429) is given off opposite the second rib, turns 

 around the dorso-cervical artery from without inward, runs forward on the lower 

 part of the lateral surface of the trachea, and ascends in the neck on the ventral 

 face of the common carotid artery. The left nerve (Fig. 428) arises from the vagus 

 where the latter begins to cross the aortic arch. It passes back over the ligamentum 



' In some cases the left vagus passes back below the junction of the jugular veins and the 

 termination of the left brachial vein. It then runs backward and somewhat dorsally across the 

 left face of the anterior vena cava to reach its usual position. 

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