888 



PAR VAGUM. 



the pharynx, to the inferior constrictor of 

 the pharynx, and also occasionally one or 

 two slender filaments to the crico-thyroid 

 muscle. It likewise sends a branch upwards 

 over the posterior surface of the larynx, first 

 passing between the oesophagus and back part 

 of the trachea, and then beneath the mucous 

 membrane of the anterior part of the pharynx 

 and crico-arytenoideus posticus muscle, sending 

 some filaments to the oesophagus and mucous 

 membrane of the pharynx, and anastomosing 

 with the posterior descending twig of the inter- 

 mil branch of the superior laryngeal. The 

 trunk of the recurrent now passes upwards in 

 front of the lower edge of the inferior constrictor 

 muscle, gets into the sulcus on the posterior 

 surface of the articulation between the lower 

 cornu of the thyroid cartilage and the external 

 surface of the cricoid cartilage, and then passes 

 along the outer edge of the crico-arytenoideus 

 posticus upon the external surface of the crico- 

 arytenoideus lateralis and thyro-arytenoid mus- 

 cles, where it terminates. In its course along the 

 side of the larynx it generally sends a twig up- 

 wards to anastomose with one of the descending 

 twigs of the internal branch of the superior 

 laryngeal. As it is passing the crico-ary- 

 tenoideus posticus it sends some twigs into the 

 external edge of that muscle, all of which enter 

 among its fibres except one. This last twig, 

 which does not enter among the fibres of the 

 muscle, runs beneath its outer edge, and pro- 

 ceeding upwards and inwards between its an- 

 terior surface and the posterior surface of the 

 cricoid cartilage, it reaches the lower edge of 

 the arytenoideus obliquus and transversus, and 

 is lost among their fibres. As the continuation 

 of the recurrent passes over the surface of the 

 cricoid-arytenoideus lateralis, it sends some fila- 

 ments inwards among the fibres of this muscle, 

 and then proceeds upwards upon the thyro-aryte- 

 noid, into the interior of which it dips. Its ter- 

 minating filaments are distributed in the thyro- 

 arytenoid muscle, and a few only can be traced to 

 the lining membrane of the larynx. We have 

 thus seen, that while nearly all the filaments of 

 the internal branch of the superior laryngeal, 

 distributed to the larynx, ultimately run to its 

 mucous surface, the greater part of the filaments 

 of the recurrent are distributed in the muscles 

 which are attached to and move the arytenoid 

 cartilages. 



The peculiarity in the course of the inferior 

 laryngeal from which it derives its name of re- 

 current, depends upon the changes in the rela- 

 tive position of the branchial arteries to the 

 larynx in the embryo, after they have assumed 

 the form presented in the adult by the arch of the 

 aorta and the large vessels which spring from it. 

 In those cases where the right subclavian artery, 

 instead of arising along with the right carotid 

 by a common trunk (arteria innominata), comes 

 off' from the arch of the aorta beyond the origin 

 of the left subclavian, or, in other words, is the 

 last in order of the large arteries which supply 

 the head and thoracic extremities, and then 

 proceeds across the spine behind the oesophagus 

 to reach its usual position behind the scalenus 

 ;inticus muscle on the right side, the recurrent 



does not arch round the right subclavian, but 

 is given off from the trunk of the vagus as it 

 is passing the larynx.* 



Course of the vagus through, the thorax. 

 After the right va;us has given off the recurrent, 

 it passes behind the ascending portion of the 

 arch of the aorta, and proceeding downwards, 

 inwards, and backwards behind the right 

 bronchus, right pulmonary artery and veins, 

 reaches the oesophagus as it lies in the posterior 

 mediastinum. The left vagus, after passing 

 from the anterior surface of the arch of the 

 aorta, also proceeds downwards, inwards, and 

 backwards behind the left bronchus, left pul- 

 monary artery and veins, and also reaches the 

 oesophagus in the posterior mediastinum at the 

 same part where the right vagus joins it. Both 

 nerves closely accompany the oesophagus down 

 the posterior mediastinum, and pass from the 

 thorax into the upper part of the abdomen 

 through the same opening (oesophageal open- 

 ing) m the diaphragm. At the upper part of 

 the chest, the vagi become flattened from before 

 backwards, and are consequently broader and 

 thinner than in the neck. 



Immediately after the vagus has given off the 

 recurrent it sends numerous twigs inwards. 

 Some of these pass upwards and inwards to 

 assist in forming the cardiac plexus ; some pro- 

 ceed transversely inwards upon the anterior 

 surface of the lower part of the trachea, and 

 anastomose with other branches from the vagus 

 arising higher up, and also with branches from 

 the recurrent and sympathetic to form the ante- 

 rior and inferior tracheal plexus (plexus trache- 

 alis anterior et inferior) ; while others pass upon 

 the posterior surface of the lower part of the 

 trachea, anastomose with other branches from 

 the recurrent and sympathetic, and thus form 

 the posterior and inferior tracheal plexus. The 

 vagus at this part also sends a few twigs upon 

 the upper part of the thoracic portion of the 

 oesophagus, forming a free anastomosis on its 

 surface with other twigs from the recurrent and 

 the posterior bronchial plexus (plexus oesopha- 

 gei thoracici superior). It likewise sends some 

 branches inwards and downwards to throw 

 themselves into the lateral portion of the lower 

 part of the cardiac plexus ; while a few others 

 pass still more downwards to reach the anterior 



* Two cases of this variety, in the origin and 

 course of the inferior laryngeal nerve and right sub- 

 clavian artery, are recorded by Dr. Stedman (Edin. 

 Med. and Surg. Journal for 1823, p. 564) and Dr. 

 Hart (in same Journal, 25th vol. 1826). I have 

 myself had an opportunity of examining two cases 

 of this kind. In those cases of double monstrosity 

 where the head and larvnx are double, and the 

 two bodies are fused together immediately below 

 this, so that the lower part of the neck, the thorax, 

 and thoracic extremities are single, and where con- 

 sequently we have four vagi nerves in the upper 

 part of the neck, and only two at the lower part, 

 the right recurrent of the right larynx hooks round 

 the subclavian artery, and the left recurrent of the 

 left larynx hooks round the arch of the aorta, 

 while the other two vagi, or the left recurrent of 

 the right larynx, and the right recurrent of the 

 left, give off their superior laryngeal branches as 

 they pass the larynges. I had an opportunity of 

 dissecting one case of this kind. 



