818 SUBCLAVIAN ARTERIES. 
in operations upon the larger blood-vessels, 
the touch often fails to discriminate the pro¬ 
per object, the characteristic pulsation of a 
arge artery being, under such circumstances, 
often wanting. 
In the postero-inferior triangle of the neck 
the artery is covered by the integument, su¬ 
perficial fascia and platysma, descending su¬ 
perficial (supra-clavicular) twigs of the cervical 
plexus, and by the external jugular vein. The 
situation of this vein in the supra-clavicular 
space, is subject to much variety ; it most fre¬ 
quently runs near to the inner boundary of 
the triangle and parallel to the outer edge of 
the sterno-mastoid muscle, but frequently de¬ 
scends in the very centre of the space ; in the 
latter case it much embarrasses the operator 
in attempting to expose the subclavian artery. 
Next in order, a number of conglobate 
glands, and a plexus of anastomosing veins, 
principally from the scapular region, come into 
view ; these latter usually communicate with 
the external jugular, or with the subclavian 
vein. Areolar tissue which presents a laminated 
arrangement encloses these glands and super¬ 
ficial vessels, and isolates them from the 
deeper-seated parts. 
These structures being removed, the sub¬ 
clavian artery appears to lie within a second 
triangle of smaller dimensions, bounded inter¬ 
nally by the scalenus anticus muscle, externally 
and superiorly by the omo-hyoid muscle, and 
inferiorly by the first rib; this bone represents 
the base of the triangle, and over it the artery 
is seen to pass. At this depth, two collateral 
arterial branches of considerable size cross 
the supra-clavicular space, the one, the trans¬ 
versale colli, above, the other, the supra¬ 
scapular, below the level of this portion of the 
subclavian artery ; the latter is placed under 
cover of the clavicle, and in contact with the 
front of the subclavian vein. As the supra¬ 
scapular artery pursues its course towards the 
shoulder, it crosses in front of the subclavian 
artery and of the brachial plexus of nerves. 
Here likewise the clavicle and the subclavius 
muscle constitute additional anterior relations 
of the subclavian artery, now near its termi¬ 
nation. 
The nervous bundle of the brachial plexus is 
parallel to the subclavian artery in its third 
stage, and lies superior and external to the 
vessel ; in its descent the lower division of 
the plexus overhangs the artery, and one or 
two of the branches (anterior thoracic) cross 
the anterior surface of the artery, and some¬ 
times even encircle it in a nervous loop. 
The anterior relations of the third stage of 
the subclavian artery may therefore be thus 
arranged : — 
1. Integument, superficial cutaneous nerves, 
platysma, fascia. 
2. Areolar tissue in layers, glands, external 
jugular vein, an intricate plexus of smaller 
veins. 
3. Anterior thoracic branches of the bra¬ 
chial plexus, the subclavian vein, supra-sca- 
pular artery, clavicle, and subclavius muscle. 
Anomalies in the origin of the subclavian ar¬ 
teries.—1. The right subclavian artery some¬ 
times arises separately from the arch of the 
aorta, in which case there is no arteria inno- 
minata ; the branches that arise from the arch 
of the aorta are then four in number, but con¬ 
siderable variety has been observed in the 
relation which the right subclavian bears to 
the other three branches ; thus, 
a. It may occupy the usual position of the 
innominate artery, being the first in order of 
the branches of the arch of the aorta ; its re¬ 
lations within the thorax will then correspond 
with those assigned to the vessel whose place 
it comes to occupy. 
b. It may be the second in numerical order 
of the branches of the arch, arising after the 
right carotid artery, behind which it subse¬ 
quently passes to arrive at its proper position 
in the neck. 
c. It may arise after the two carotids as the 
third branch of the arch ; or, 
d. It may be the last branch of the aorta, and 
occupy the usual situation of the left sub¬ 
clavian artery. Of the varieties already men¬ 
tioned, this is the most frequently met with, 
and, according to the statistics of Pro¬ 
fessor Quain, it occurs once in every 250 
examinations. 
e. Sometimes (but much more rarely) this 
vessel arises below the arch, from the thoracic 
aorta, and its position may be so low, that it 
will furnish some of the upper intercostal 
arteries. 
The course of the artery, when it thus arises 
from the left of the arch, is very remarkable ; 
it crosses in front of the spinal column, either 
behind the oesophagus, or between that tube 
and the trachea, and necessarily passes across 
the neck behind all the other branches given 
off from the arch of the aorta. When thus ab¬ 
normally situated behind the oesophagus, it 
has been accidentally wounded by a foreign 
body which had first transfixed that tube. A 
remarkable example of this occurrence is 
mentioned by Mr. Kirby, in the 2d vol. of the 
Dublin Hospital Reports. 
The irregularity in question, of the right 
subclavian artery, was regarded by Dr. Bay- 
ford as the cause of difficult deglutition, in a 
case which had been accurately observed for 
many years, and this new disease, as he con¬ 
sidered it, he quaintly termed “ Dysphagia 
lusoria.” * 
In those instances, where the right sub¬ 
clavian artery has been found to deviate thus 
strangely from its usual course, the inferior 
laryngeal nerve presented a remarkable change 
of direction, depending no doubt on the altered 
course of the artery ; in all the instances 
which were noted, the nerve was given off 
from the pneumogastric, higher up than usual, 
and passed directly to the larynx, so as not to 
be entitled to the name of “recurrent.” Dr. 
Hart, who first directed attention to this fact, 
has thus clearly explained the connection be¬ 
tween the unusual position of the artery and 
* Memoirs of the Medical Society of London, 
vol. ii. 1793.