e of the
cervical and axillary regions, together with their line of union beneath
the clavicle, c*, Plate 12, R, Plate 11, which serves to divide them
surgically.

In the neck, the subclavian artery, B, Plate 11, is seen to be separated
from the subclavian vein, A, by the breadth of the anterior scalenus
muscle, D, as the vessels arch over the first rib, F. In this region of
the course of the vessels, the brachial plexus of nerves, C, ranges
along the outer border of the artery, B, and is separated by the artery
from the vein, A, as all three structures pass beneath the clavicle, R,
and the subclavius muscle, E. From this latter point the vessels and
nerves take the name axillary, and in this axillary region the relative
position of the nerves and vessels to each other and to the adjacent
organs is somewhat changed. For now in the axillary region the vein, a,
is in direct contact with the artery, b, on the forepart and somewhat to
the inner side of which the vein lies; while the nerves, D, d, Plate 12,
embrace the artery in a mesh or plexus of chords, from which it is often
difficult to extricate it, for the purpose of ligaturing, in the dead
subject, much less the living. The axillary plexus of nerves well merits
the name, for I have not found it in any two bodies assuming a similar
order or arrangement. Perhaps the order in which branches spring from
the brachial plexus that is most constantly met with is the one
represented at D, Plate 12, where we find, on the outer border of B, the
axillary artery, a nervous chord, d, giving off a thoracic branch to
pass behind H, the lesser pectoral muscle, while the main chord itself,
d, soon divides into two branches, one the musculo-cutaneous, e, which
pierces G, the coraco-brachialis muscle, and the other which forms one
of the roots of the median nerve, h. Following that order of the nerves
as they are shown in Plate 12, they may be enumerated from without
inwards as follows:--the external or musculo-cutaneous, e; the two roots
of the median, h; the ulnar, f; the musculo-spiral, g; the circumflex,
i; close to which are seen the origins of the internal cutaneous, the
nerve of Wrisberg, some thoracic branches, and posteriorly the
subscapular nerve not seen in this view of the parts.

The branches which come off from the axillary artery are very variable
both as to number and place of origin, but in general will be found
certain branches which answer to the names thoracic, sub