556 BLOOD-VASCULAR SYSTEM OF THE HORSE 



Arteries of the Thoracic Limb 



THE brachial ARTERY 



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 sub- 

 scapular 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.^ 



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 ]3art 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 l^order 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 he 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 inter- 

 stice 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 fasciae antibrachii 

 it gives off the following named l^ranches: 



(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. 



(6) The posterior circumflex artery (A. circumfiexa humeri posterior) arises 

 a little above the preceding vessel antl passes outward ])ehind 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 

 arter^^ 



(c) The circumflex artery of the scapula (A. circumfiexa scapula?) 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 supras]iinatus, 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. 



' The term axillary is often applied to the artery from the first ril) to the point of origin of 

 the subscapular brancli. 



