The Vascular System 219 
The left subclavian artery, sc.s., although it has a 
different origin, has the same branches as described 
in connection with the right subclavian. The 
exact order in which the first of these (the thyroid, 
th; the internal mammary, im‘; the collateralis 
colli, cc; the pleural, plu; and the vertebral, v’) 
are given off is, as might be expected, subject to 
some variation. 
The collateralis colli, cc (following Bronn’s 
nomenclature), whose origin was noted above, 
will now be discussed; since the two are alike only 
one need be described. After leaving the sub- 
clavian, it passes cephalad, at the side of the trachea 
and cesophagus, in company with the internal 
jugular vein, so that in this part of its course 
it would seem to be the internal carotid artery. It 
gives numerous small twigs to the trachea and 
cesophagus, oe. In the region of the posterior part 
of the huge jaw muscle it is connected directly, x, 
with the adjacent branch, cm (called by Bronn the 
common carotid) of the primary carotid, and 
indirectly, x',with a complicated group of branches 
from the common carotid. Cephalad to the 
connective x’, which extends dorsad and is hence 
foreshortened in the figure, the collateralis colli 
gives off a small vessel, y (too largein Fig. 62), tothe 
shoulder and skin; it then sends a fairly large 
branch, jm, into the large jaw muscle, close to 
which it now lies. Next a small branch, lg, is sent 
to the larynx. Continuing cephalad and laterad 
