556 BLOOD-VASCULAR SYSTEM OF THE HORSE 



Arteries of the Thoracic Limb 



THE brachial ARTERY 



The brachial artery, after turning around the lower Ijorder of the scalenus at 

 the first rib, passes backward and a little downward across the origin of the coraco- 

 bracliialis 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 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 arter}^ 

 The chief branches are as follows: 



1. The suprascapular artery (A. thoracico-acromialis) is a small and someAvhat 

 flexuous vessel, which arises near the anterior liorder 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 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 fascia antibrachii 

 it gives off the following named branches : 



(a) The thoracico-dorsal (A. thoracicodorsalis) is a long arterj^ 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 latissinuis dorsi. It gives 

 branches to these muscles, the alxlominal panniculus and the axillary lymph glands. 



(&) 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 tricei^s 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 scapuke) arises about 

 two or three inciics (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 simihir fashion on the costal surface of the scapula and suppHes 

 branches to the subscai:)uhiris. 



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

 the subscapular branch. 



