888 
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 esophagus 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 esophagus and mucous 
membrane of the pharynx, and anastomosing 
with the posterior descending twig of the inter- 
nal 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 cesophagus 
to reach its usual position behind the scalenus 
anticus muscle on the right side, the recurrent 
PAR VAGUM. 
does not arch round the right subclavian, but 
is given off from the trunk of the vagus as it 
is ing the larynx.* 
Cinires of the t vagus through the thorax.— 
After the right vagus 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 cesophagus as it lies in the posterior 
mediastinum. The deft vagus, after passing 
from the anterior surface of the arch of the 
aorta, also proceeds downwards, inwards, and 
backwards Fehind the left bronchus, left pul- — 
monary artery and veins, and also reaches the — 
cesophagus in the posterior mediastinum at the 
same part where the right vagus joins it. Both 
nerves closely accompany the esophagus down 
the posterior mediastinum, and from the 
thorax into the upper part of abdomen 
through the same opening (esophageal open- 
ing) in the diaphragm. At the upper part of * 
the chest, the vagi become flat 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 th 
trachea, anastomose with other branches from 
the recurrent and sympathetic, and thus fe 
the posterior and inferior tracheal plexus. 
vagus at this part also sends a few twigs upon 
the upper part of the thoracic portion of the 
cesophagus, forming a free anastomosis on its 
surface with other twigs from the recurrent and — 
tlie posterior bronchial plexus (plexus a@sopha- 
gei thoracici superior). It likewise sends some 
branches inwards and downwards to throw 
themselves into the lateral portion of the low 
part of the cardiac plexus; while a few other 
pass still more downwards to reach the anterior 
* Two cases of this variety, in the origin 
course of the inferior laryngeal nerve and righ 
clavian artery, are recorded by Dr. Stedman ( 
Med. and Surg. Journal for 1823, p. 564) and 
Hart (in same Journal, 25th vol. 1826). I ha 
myself had an opportunity of examining two ¢ 
of this kind. In those cases of double mor 
where the head and larynx are double, and # 
two bodies are fused together immediately bel 
this, so that the lower part of the neck, the thor 
and thoracic extremities are single, and wh ce 
sequently we have four vagi nerves in the up 
part of the neck, and only two at the lower p 
the right recurrent of the right larynx hooks rour 
the subclavian artery, and the left recurrent of th 
left larynx hooks round the arch of the aor 
while the other two vagi, or the left recurrent ¢ 
the right larynx, and the right recurrent of th 
left, give off their superior | branches % 
they pass the larynges. I had an opportunity 0 
dissecting one case of this kind. 
aaa 
~~ 
