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muscles, and to the parietes of the thorax, and anastomoses with the internal mammary and intercostal arteries.
  2. The thoracoacromial artery (a. thoracoacromialis; acromiothoracic artery; thoracic axis) is a short trunk, which arises from the forepart of the axillary artery, its origin being generally overlapped by the upper edge of the Pectoralis minor Projecting forward to the upper border of this muscle, it pierces the coracoclavicular fascia and divides into four branches—pectoral, acromial, clavicular, and deltoid. The pectoral branch descends between the two Pectorales, and is distributed to them and to the mamma, anastomosing with the intercostal branches of the internal mammary and with the lateral thoracic. The acromial branch runs lateralward over the coracoid process and under the Deltoideus, to which it gives branches; it then pierces that muscle and ends on the acromion in an arterial network formed by branches from the transverse scapular, thoracoacromial, and posterior humeral circumflex arteries. The clavicular branch runs upward and medialward to the sternoclavicular joint, supplying this articulation, and the Subclavius. The deltoid (humeral) branch, often arising with the acromial, crosses over the Pectoralis minor and passes in the same groove as the cephalic vein, between the Pectoralis major and Deltoideus, and gives branches to both muscles.
  3. The lateral thoracic artery (a. thoracalis lateralis; long thoracic artery; external mammary artery) follows the lower border of the Pectoralis minor to the side of the chest, supplying the Serratus anterior and the Pectoralis, and sending branches across the axilla to the axillary glands and Subscapularis; it anastomoses with the internal mammary, subscapular, and intercostal arteries, and with the pectoral branch of the thoracoacromial. In the female it supplies an external mammary branch which turns round the free edge of the Pectoralis major and supplies the mamma.
  4. The subscapular artery (a. subscapularis) the largest branch of the axillary artery, arises at the lower border of the Subscapularis, which it follows to the inferior angle of the scapula, where it anastomoses with the lateral thoracic and intercostal arteries and with the descending branch of the transverse cervical, and ends in the neighboring muscles. About 4 cm. from its origin it gives off a branch, the scapular circumflex artery.

FIG. 524– The scapular and circumflex arteries. (See enlarged image)

  The Scapular Circumflex Artery (a. circumflexa scapulæ; dorsalis scapulæ artery) is generally larger than the continuation of the subscapular. It curves around the axillary border of the scapula, traversing the space between the Subscapularis above, the Teres major below, and the long head of the Triceps laterally (Fig. 524); it enters the infraspinatous fossa under cover of the Teres minor, and anastomoses with the transverse scapular artery and the descending branch of the transverse cervical. In its course it gives off two branches: one (infrascapular) enters the subscapular fossa beneath the Subscapularis, which it supplies, anastomosing with the transverse scapular


