THE BRACHIAL ARTERY. 773 



(a) Thoracic branches (rami thoracodorsales) , which supply the serratus magnus and the 

 muscles of some of the intercostal spaces, and not far from its origin it gives oflf — 



{d) The dorsal scapular (a. circumflex scapulae). This vessel, of large size, winds around 

 the axillary border of the scapula in the triangular space bounded by the teres major, the teres 

 minor, and the long head of the triceps, and is distributed to the infraspinatus and the teres 

 minor. 



The subscapular artery anastomoses through its thoracic branches with the intercostals and 

 with the long thoracic, and through the dorsal scapular witli the suprascapular and posterior 

 scapular arteries. 



Variations. — The subscapular artery varies somewhat in its origin. Occasionally it springs 

 from the second portion of the axillary, and may also arise from the brachial. Quite frequently 

 it arises from a trunk common to it and one or other or both circumflex arteries, and the supe- 

 rior profunda brachii, normally a branch of the brachial artery, may also arise from this common 

 trunk. 



The subscapular has been observed to give rise to an aberrant artery which passes down 

 the arm and either unites with the brachial or else becomes the ulnar, or may even extend to 

 the neighborhood of the wrist, where it unites with a branch of the anterior interosseous artery 

 to form the radial. 



6. The Anterior Circumflex Artery, — The anterior circumflex (a. circum- 

 flexa humeri anterior) (Fig. 704) is the smallest of the three branches of the third 

 portion of the axillary, and arises either directly from the artery or from a common 

 trunk with the posterior circumflex ; more rarely it arises from the subscapular. It 

 passes outward beneath the coraco-brachialis and the heads of the biceps, and winds 

 around the surgical neck of the humerus, lying close to the bone. Opposite the 

 bicipital groove it gives off a branch which ascends along the groove to be distributed 

 to the capsule of the shoulder-joint, and it also sends branches to the coraco- 

 brachialis and biceps. It terminates by anastomosing with the posterior circumflex 

 and with the humeral branch of the acromial thoracic. 



7. The Posterior Circumflex Artery. — The posterior circumflex (a. cir- 

 cumtlexa humeri posterior) (Fig. 704) arises from the axillary, almost opposite the 

 anterior circumflex, or from a common trunk with that vessel or with the subscap- 

 ular. More rarely it may arise from the upper part of the brachial artery. It passes 

 backward and outward through the quadrilateral space bounded by the subscapularis 

 above, the teres major below, the long head of the triceps internally, and the 

 humerus externally, and winds around the posterior surface of that bone at the level 

 of its surgical neck. Passing under the deltoid muscle externally, it divides into 

 a number of branches, most of which pass into the muscle to supply it, while some 

 pass to the shoulder-joint. It anastomoses with the acromial branch of the acromial 

 thoracic, with the anterior circumflex, and with the superior profunda branch of the 

 brachial. 



THE BRACHIAL ARTERY. 



The brachial artery (a, brachialis) (Figs. 708, 709) is the continuation of the 

 axillary down the arm. It begins at the lower border of the teres major and termi- 

 nates a little below the bend of the elbow by dividing into the radial and ulnar 

 arteries. In the upper part of its course the vessel lies along the inner side of the 

 arm, but as it passes downward it inclines somewhat outward, so that in its lower 

 part it is on the anterior surface of the brachium. Its course may be indicated by a 

 line drawn from the junction of the outer and middle thirds of the folds of the axilla 

 to a point midway between the condyles of the humerus. 



Relations. — Anteriorly the brachial artery is covered throughout the greater 

 part of its course by only the deep and superficial fasciae and the integument. About 

 the middle of its length it is crossed obliquely, from without inward, by the median 

 nerve, and at the bend of the elbow it passes beneath the aponeurotic slip, the 

 so-called bicipital fascia (lacertus fibrosus) from the tendon of the biceps, and is 

 separated by it from the median basilic vein. Posteriorly it rests in succession, from 

 above downward, upon the long head of the triceps, the inner head of the triceps, 

 the insertion of the coraco-brachialis, and the brachialis anticus. The musculo-spiral 

 nerve and the superior profunda artery pass downward and inward between the 

 vessel and the long head of the triceps. Externally to it, above, is the median nerve 



