Branches.—The axillary artery usually gives off six branches, viz.; 1. the acromial ; 2. the superior thoracic ; 3. the inferior or long tho racic or external mammary ; 4. the subscapu lar ; 5. the posterior circumflex ; 6. the ante rior circumflex.
1. The acromial artery (thoraeica acromia lis) arises from the anterior side of the axillary artery above the edge of the lesser pectoral muscle, and after having given off some branches to the subclavius, serratus magnus, and first intercostal, it passes obliquely down wards and outwards, piercing the expansion of the costo-coracoid ligament, and arrives at the posterior surface of the deltoid muscle, where it divides into a superior and an inferior branch.
The superior branch mounts by a tortuous course towards the clavicle ; this branch, which is more particularly designated by the term acromial, after having given off one or more branches to the deltoid muscle and the integu ments, runs along the anterior border of the clavicle, behind the origin of the deltoid, until it arrives at the acromial end of that bone, where it is expended in a number of branches which go to supply the scapulo-clavicular and scapulo-humeral articulations, and also the supra-spinatus and deltoid muscles. This ar tery anastomoses with the supra-scapular and posterior circumflex in the vicinity of the acro mion process. The inferior or cephalic branch descends in company with the cephalic vein in the cellular interval between the deltoid and pectoralis major muscles, and is distributed to these muscles and the integuments.
2. The superior thoracic (thoracica suprema, Seem.) is very irregular as to the place of its origin, coming as frequently from the acromial as from the trunk of the axillary; it passes ob liquely forwards between the greater and lesser_ pectoral muscles, and divides into several branches, which are distributed to these two muscles, the integuments, and more deeply to the serratus magnus and the two or three supe rior intercostal muscles, anastomosing with the intercostal and internal mammary arteries.
3. The inferior thoracic (thoracica longior or mammaria externa) is subject to the same variety of origin as the superior thoracic; it sometimes arises from the subscapular. This artery descends on the surface of the serratus magnus muscle along the inferior border of the pectoralis major; its :branches are distributed to the glands and cellular tissue of the axilla, to the serratus magnus, and pectoralis major and minor, and the intercostal muscles ; it also supplies the mammary gland and the integu ments ; it anastomoses with the intercostal, in ternal mammary, superior thoracic, and sub scapular arteries.
Scemmerring describes a fourth thoracic ar tery, under the name of alaris sive axillaris glandulosa,* which is distributed principally to the axillary lympathic glands; this artery is very irregular in its origin, sometimes coming from the trunk of the axillary artery, and as often arising from the thoracica longior or the subscapularis. Instead of a single artery going to the glands of the axilla, these parts are more usually supplied by several small twigs which arise from the arteries in their vicinity.
4. The subscapular artery is generally the largest branch of the axillary ; it arises at the lower edge of the subscapularis muscle, lying at its origin behind the brachial plexus; it gives three or four branches to the glands and cellular tissue of the axilla and to the subscapularis muscle, after which it divides into two branches, one inferior, the smaller, the other, larger, called the external scapular. The inferior branch de
scends along the inferior border of the subsca pularis muscle and the inferior costa of the scapula between the latissimus dorsi and the serratus magnus, to which muscles, the teres major, and the integuments it is finally distributed, anastomosing with the posterior scapular artery at the inferior angle of the scapula. The external branch, circunjlexus scapula of Scemmering, passes backwards through a triangular space formed by the sub scapularis above, the teres major inferiorly, and the tendon of the long head of the triceps ex ternally, and after having given several branches to these muscles, it divides into two branches, a superficial and a deep-seated ; the superficial branch is distributed to the teres major, teres minor, infra-spinatus, latissimus dorsi, and the integuments; the deep-seated branch winds round the neck of the scapula under the teres major, and entering the fossa infra-spinata, supplies the infra-spinatus muscle, the scapula, and the scapulo-humeral articulation. This branch anastomoses freely with the branch of the supra-scapular, which descends under the root of the acromion process.
5. The posterior circurVex, next to the sub scapular, is the largest branch of the axillary artery, from the posterior side of which it arises; frequently it comes from the infra-scapular. It passes backwards through a quadrilateral space, bounded in front by the neck of the humerus, behind by the long head of the triceps, above by the subscapularis, and below by the teres major; coursing round the neck of the humerus, it passes below the inferior edge of the teres minor, and attaching itself to the under surface of the deltoid, is principally distributed to that muscle, giving branches in its course to the capsular ligament of the shoulder-joint, the subscapularis, teres major and minor, infra spinatus, and triceps ; 'it anastomoses with the supra-scapular and acromial thoracic by branches which it sends to the acromion, and with the anterior circumflex by the branches which it gives to the articulation of the shoulder.
6. The anterior circumflex is a very small vessel, arising either from the axillary or the posterior circumflex; it passes forwards round the neck of the humerus under the coraco-bra chialis and short head of the triceps, to both of which muscles it gives branches; arriving at the bicipital groove, it sends off several branches, some of which descend along that groove, and others spread over the surface of the head and neck of the humerus, supplying that part of the bone and the tendons which are inserted into its tuberosities ; while the continuation of the vessel entering the bicipital groove ascends by the side of the tendon of the long head of the biceps, passes under the capsular ligament, to which and the other parts entering into the formation of the shoulder-joint it is ultimately distributed. This artery anastomoses with the posterior circumflex and ascending branches of the superior profunda of the brachial artery.
For the Bibliography see that of ANATOMY (INTRODUCTION) and of ARTERY.
(J. Hart.)