The =brachial artery=, after turning around the lower border of the
scalenus at the first rib, passes backward and a little downward across
the origin of the coraco-brachialis and the insertion of the
subscapularis muscle at the inner side of the shoulder joint. At the
posterior border of the subscapularis it gives off the subscapular
artery, and turns downward on the inner surface of the arm. In its
course in the arm it inclines a little forward, crosses the humerus very
obliquely, and divides at the antero-internal aspect of the distal third
of the shaft of the bone into the anterior and posterior radial
arteries.[162]
It is related internally to the serratus magnus and the posterior deep
pectoral muscles, and the cubital lymph glands. Externally it lies on
the subscapularis, the brachialis, the insertion of the teres major and
latissimus dorsi, and the inner head of the triceps. The
coraco-brachialis muscle lies along the front of the artery, which,
however, overlaps the muscle distally. The vein crosses the inner face
of the artery and runs down behind it, accompanied part way by the ulnar
and radial nerves. The musculo-cutaneous and median nerves form a loop
around the artery close to its origin, and the latter nerve then passes
down in front of the artery. The chief branches are as follows:
1. The =suprascapular artery= (A. thoracico-acromialis) is a small and
somewhat flexuous vessel, which arises near the anterior border of the
subscapularis, runs upward, and dips in between that muscle and the
supraspinatus. It gives branches to these muscles, the anterior deep
pectoral, and the mastoido-humeralis. A branch passes in front of the
coraco-brachialis to the shoulder joint and the proximal end of the
humerus.
This vessel may be double, or be represented by one or more branches
of the inferior cervical artery.
2. The =subscapular artery= (A. subscapularis) is a very large vessel
which arises at the posterior border of the subscapularis muscle. It
passes upward in the interstice between that muscle and the teres major
on the inner surface of the long head of the triceps, turns around the
posterior border of the scapula below the posterior angle, and ends in
the infraspinatus and deltoid. Besides collaterals (Rami musculares) to
the subscapularis, teres major, triceps, and tensor fasciæ antibrachii
it gives off the following named branches:
(_a_) The =thoracico-dorsal= (A. thoracicodorsalis) is a long artery
which is usually given off about an inch from the origin of the
subscapular, crosses the inner face of the teres major, and runs upward
and backward on the latissimus dorsi. It gives branches to these
muscles, the abdominal panniculus and the axillary lymph glands.
(_b_) The =posterior circumflex artery= (A. circumflexa humeri
posterior) arises a little above the preceding vessel and passes outward
behind the shoulder joint between the long and external heads of the
triceps with the axillary (or circumflex) nerve. It gives branches to
these muscles, the joint capsule, and the muscles and skin of the outer
side of the shoulder, anastomosing with the anterior circumflex artery.
(_c_) The =circumflex artery of the scapula= (A. circumflexa scapulæ)
arises about two or three inches (ca. 5 to 7.5 cm.) above the shoulder
joint, passes forward to the posterior border of the scapula, and
divides into two branches. The outer one runs forward on the external
surface of the scapula below the spine and gives branches to the
supraspinatus, infraspinatus, and teres minor. The inner branch passes
forward in a similar fashion on the costal surface of the scapula and
supplies branches to the subscapularis.
[Illustration: