THE VAGUS NERVE. 



1271 



the root of the neck as the vagus crosses the anterior surface of the subclavian artery, 

 from which point it passes under and behind the artery and ascends. The left nerve 

 takes it's origin as the vagus crosses the anterior aspect of the aortic arch, and after 

 passing below and behind the arch, lateral to the obliterated ductus arteriosus, ascends 

 in the superior mediastinum to enter the neck. After entering the neck the further 

 course of the nerve is the same on both sides. It passes upward posterior to the 

 carotid sheath, either anterior or posterior to the inferior thyroid artery, occupies the 



Fig. ioSo. 



Superior cervical cardiac branch of sympathetic 



Sympathetic cord 

 Right vagus nerve 



Middle cervical ganglion 



Inferior cervical ganglion 



Superior cervical cardiac of vagus 



Middle and inf. cervical cardiac 

 branches of sympathetic 



Recurrent laryngeal nerve 



Pulmonary branch of vagus 



Vena azygos major 



Phrenic nerve 



Right pulmonary artery 



Pulmonary vein 

 Aorta 



Right auricular appendix 

 Pericardium 



Superior cervical cardiac branch 



of sympathetic 

 Superior cervical cardiac branch of vagus 

 Middle cervical ganglion 

 Middle cervical cardiac branch 



of sympathetic 



[of sympathetic 

 Inf. cervical cardiac branch 

 Inf. cervical ganglion 



Middle cervical cardiac 



branch of vagus 

 Inf cer\ical cardiac 



branch of vagus 

 Phrenic nerve 



Left \agus nerve 



Recurrent laryngeal nerve 



Left pulmonary artery 

 Pulmonary veins 



^?uln\onary orifice 



Mesial surface of lung 

 Pericardium 



Dissection showing cardiac branches of pneumogastric ner\'es and of sympathetic cords ; aortic arch and branches 

 and pulmonary artery partially removed ; pericardium laid open. 



groove between the oesophagus and the trachea, and, dipping beneath the lower 

 edge of the inferior constrictor of the pharynx, enters the larynx at the inferior 

 margin of the cricoid cartilage. 



The asymmetry observed in the first part of the course of the nerves of the two sides is 

 secondary and referable to the changes incident to the development of the large arterial trunks. 

 In the foetus both nerves hook around the fourth aortic arch of the corresponding sides and 

 are, therefore, for a time symmetrically disposed. Since, however, on the left side this arch 

 becomes the arch of the aorta, and on the right the innominate and subclavian arteries (page 

 726), it is evident that the vagi, although retaining their primary associations, later alter their 

 actual position and relations in consequence of the unequal growth and downward displacement 

 which these blood-vessels undergo. 



Branches. — During its course the inferior laryngeal nerve gives off : (a) the 

 cardiac^ (^) the tracheal^ (c) the oesophageal, id) the muscular and {e) the terminal 

 branches. 



