258 FASCIA AND MUSCLES OF THE HORSE 



may be regarded as replacing the internal ligament of the latter. A small bursa 

 may occur here. 



Relations. — Superficially, the scapula and shoulder joint, the supraspinatus, 

 triceps, and teres major muscles; deeply, the serratus magnus muscle, the bra- 

 chial vessels, and the chief branches of the brachial plexus. The subscapular 

 vessels run along or near the posterior edge of the muscle. 



Blood-supphj. — Subscapular artery, 



Nerve-supphj. — Subscapular nerves (from the brachial plexus). 



2. Teres major (Teres internus; adductor of the arm).^ — This muscle is flat, 

 widest about its middle, and lies chiefly on the deep face of the triceps. 



Origin. — The dorsal angle and the adjacent part of the posterior border of 

 the scapula. 



Insertion. — The tubercle on the inner surface of the shaft of the humerus, in 

 common with the latissimus dorsi. 



Action. — To flex the shoulder joint and adduct the arm. 



Structure. — It is for the most part fleshy, but the origin consists of an apo- 

 neurosis which blends with that of the tensor fasciae antibrachii. The insertion 

 is by a flat tendon which fuses with that of the latissimus dorsi. 



Relations. — Superficially, the triceps, infraspinatus, and deltoid muscles; 

 deeply, the serratus magnus muscle. The subscapular vessels lie in a groove 

 between the anterior edge of this muscle and the posterior border of the subscapu- 

 laris; near the shoulder joint the posterior circumflex artery and the axillary 

 nerve emerge between the two muscles. The deep face of the muscle is crossed 

 by the thoracic branches of the brachial plexus, and by the branch of the subscap- 

 ular artery which supplies the latissimus dorsi. 



Blood-supply. — Subscapular artery. 



Nerve-supply. — Axillary nerve. 



3. Coraco-brachialis (Coraco-humeralis). — This muscle lies on the inner sur- 

 face of the shoulder joint and the arm. 



Origin. — The coracoid process of the scapula. 



Insertion. — (1) A small area above the internal tul^ercle of the humerus; 

 (2) the middle third of the anterior surface of the humerus. 



Action. — To adduct the arm and to flex the shoulder joint. 



Structure. — The long tendon of origin emerges between the subscapularis 

 and the inner branch of the supraspinatus. It passes over the terminal part of 

 the subscapularis and is provided with a synovial sheath. The muscular part 

 spreads out and divides into two portions. The smaller and shorter portion is 

 inserted into the proximal third of the shaft of the humerus, close to the origin 

 of the lateral head of the triceps; the larger and longer portion is inserted into the 

 middle third of the humerus, in front of the internal tubercle and the inner head 

 of the triceps. 



Relations. — Externally, the subscapularis nniscle and the humerus; inter- 

 nally, the deep pectoral and l)rachialis nniscles. The anterior circumflex artery 

 and the nerve to the biceps usually emerge between the two insertions, and the 

 brachial vessels lie along the posterior border of the muscle. 



Blood-supply. — Anterior circumflex artery. 



Nervc-><}tpply. — Musculo-c'utaneous nerve. 



4. Capsularis (Scapulo-humcralis posticus s. gracilis). — This is a very small 

 muscle, which lies on the back of the capsule of the shoulder joint. 



Origin. — The scapula, close to the rim of the glenoid cavity. 



Insertion. — The ])osterior surface^ of the shaft of the humerus, a short distance 

 below the head. 



Action. — It may perhaps tense the capsule of the shoulder joint and prevent 

 its being pinched during flexion. 



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