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.