, Of these two vessels, the left one
arising, in general, from the arch of the aorta, is longer than the
right one by the measure of the innominate artery from which the right
arises. When either of the common carotids is tied, the circulation will
be maintained through the anastomosing branches of the opposite vessels
as above specified. When the vertebral or the inferior thyroid branch
arises from the middle of the common carotid, this vessel will have an
additional source of supply if the ligature be applied to it below the
origin of such branch. In the absence of the innominate artery, the
right as well as the left carotid will be found to spring directly from
the aortic arch.

XIV.--The subclavian arteries. When a ligature is applied to the inner
third of this vessel within its primary branches, the collateral
circulation is carried on by the anastomoses of the arteries above
mentioned; but if the vertebral or the inferior thyroid arises either
from the aorta or the common carotid, the sources of arterial supply in
respect to the arm will, of course, be less numerous. When the outer
portion of the subclavian is tied between the scalenus and the clavicle,
while the branches arise from its inner part in their usual position and
number, the collateral circulation in reference to the arm is maintained
by the following anastomosing branches:--viz., those of the
superficialis colli, and the supra and posterior scapular, with those of
the acromial thoracic; the subscapular, and the anterior and posterior
circumflex around the shoulder-joint, and over the dorsal surface of
the scapula; and those of the internal mammary and superior intercostal,
with those of the thoracic arteries arising from the axillary. Whatever
be the variety as to their mode or place of origin, the branches
emanating from the subclavian artery are constant as to their
destination. The length of the inner portion of the right subclavian
will vary according to the place at which it arises, whether from the
innominate artery, from the ascending, or from the descending part of
the aortic arch.

XV.--The axillary artery. As this vessel gives off throughout its whole
length, numerous branches which inosculate principally with the
scapular, mammary, and superior intercostal branches of the subclavian,
it will be evident that, in tying it above its own branches, the
anastomotic circulation will with much greater freedom be maintained in
respect to the arm,