300 FASCIiE AND MUSCLES OF THE HORSE 



B. Medial Groxjp 



1. Subscapularis.— This muscle occupies the subscapular fossa, beyond which, 

 however, it extends both before and behind. 



Origin. — The subscapular fossa. 



Insertion. — The posterior eminence of the medial tuberosity of the humerus. 



Action. — To adduct the humerus. 



Structure. — The muscle is fiat and triangular. The base is thin and inter- 

 digitates -ndth the scapular attachments of the serratus ventralis. Distally the 

 belly thickens and becomes narrower. It is covered by an aponeurosis, and con- 

 tains a considerable amount of tendinous tissue. The tendon of insertion is crossed 

 by the tendon of origin of the coraco-brachialis; it is intimately adherent to the cap- 

 sule of the shoulder joint, and may be regarded as replacing the medial ligament of 

 the latter. A small bursa usually is present between the tendon and the tuberosity 

 of the humerus. 



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

 triceps, and teres major muscles; deeply, the serratus ventralis 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-supply. — Subscapular artery. 



Nerve-supply. — Subscapular nerves. 



2. Teres major. — This muscle is fiat, widest about its middle, and lies chiefly 

 on the medial face of the triceps. 



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

 the scapula. 



Insertion. — The teres tubercle 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 apoy" 

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

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



Relations. — Laterally, the triceps; medially, the serratus ventralis. The sub- 

 scapular vessels lie in a groove between the anterior edge of this muscle and the 

 posterior border of the subscapularis; near the shoulder joint the posterior cir- 

 cumflex artery and the axillary nerve emerge between the two muscles. The 

 medial face of the muscle is crossed by the thoracic branches of the brachial plexus, 

 and by the artery which supplies the latissimus dorsi. 



Blood-supply. — Subscapular artery. 



Nerve-supply. — Axillary nerve. 



3. Coraco-brachialis.' — This muscle lies on the medial surface of the shoulder 

 joint and the arm. 



Origin. — The coracoid process of the scapula. 



Insertion. — (1) A small area above the teres tubercle 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 medial branch of the supraspinatus. It passes over the terminal part of the 

 subscapularis and is provided with a synovial sheath. The belly spreads out and 

 divides into two parts. The small, short part is inserted into the proximal third of 

 the medial surface of the shaft of the humerus; the large, long part is inserted into 

 the middle third of the humerus, in front of the teres tubercle and the medial head of 

 the triceps. 



' Also termed the coraco-humeralis. 



