TERES MINOR— SUBSCAPULARIS 303 



Structure. — Its origin is by fleshy til)res which converge outwards in bipenni- 

 forni fashion iii)(>n the tendon. Frequently that part which arises from the lower 

 surface of the s|)ine of the scapula overlies and is somewhat separate from the rest. 

 Its insertion into the capsule and tul)erosity is by a tendon which is almost entirely 

 concealed by fleshy fibres. 



Nerve-supply. — From the brachial plexus (through the fifth cervical nerve), 

 by the suprascapular branch which enters the deep surface of the muscle at its 

 outer part and near its upper border. 



Action. — It is the chief external rotator of the humerus. This movement of 

 external rotation is through about 90°, and is of great importance. When the 

 elbow is bent, it produces the lateral movement of the hand by which, in writing, 

 the pen is carried from left to right across the page, ^^'hen the elljow is extended, 

 the rotation of the humerus adds considerably to the range of rotatory movement 

 enjoyed by the hand. The infra-spinatus also adducts the elevated arm, at the 

 same time drawing it slightly backwards, or extending it. It helps to hold the 

 head of the humerus in contact with the glenoid cavitA\ 



Relations. — Superficially, the infraspinous fascia which separates it from the 

 deltoid, trapezius, and latissimus dorsi; deeply, the suprascapular and dorsalis 

 scapulae vessels, and sometimes a small bursa which intervenes between its tendon 

 and the capsule of the shoulder-joint; externally, the teres major and minor. 



Variations. — The slip from the under surface of the spine is frequently almost as separate 

 from the iufra-spinatus as the teres minor, and sometimes there is no separation between the 

 infra- s}iinatus and teres minor. 



4. TERES MINOR 



The teres minor — named from its Ijeing the lesser of two somewhat cylindrical 

 muscles {tere^ =^ round or cylindrical) — is a thick but narrow triangular or fan- 

 shaped sheet. 



Origin. — (1) The impression which occupies the upper two-thirds of the 

 axillary Ijorder of the infraspinous fossa; (2) septa which separate it from the 

 infra-spinatus behind, and the teres major in front. 



Insertion. — (1) The lowest of the three facets on the greater tuberosity of the 

 humerus and the posterior surface of that bone for one inch (2 '5 cm.) below the 

 facet; (2) the capsule of the shoulder-joint. 



Structure. — From a fleshy origin which terminates in a point below, its fibres 

 pass upwards and outwards to their insertion, which is by a short strong tendon 

 into the lowest facet on the tuberosity, and the capsule of the shoulder-joint; below 

 the facet it is inserted by fleshy or very short tendinous filires. 



Nerve-supply. — From the posterior cord of the brachial plexus (through the 

 fifth cervical nerve) by the lower division of the circumflex nerve which enters the 

 muscle upon its anterior surface near its insertion. The nerve is remarkable on 

 account of the ganglion upon its trunk shortly before it passes into the muscle. 



Action. — The same as that of the preceding muscle, of which it may be con- 

 sidered to form a part. It will therefore rotate the arm outwards and at the same 

 time adduct. 



Relations. — Behind, the deltoid; in front, the long head of the triceps, the 

 teres major, and subscapularis. Above and internally, the dorsalis scapula? vessels 

 run between it and the axillary border of the scapula. 



5. SUBSCAPULARIS 



The subscapularis muscle — named from its position beneath the scapula — is 

 a thick triangular and somewhat multipenniform sheet. 



Origin. — (1) The whole of the ventral surface of the scapula with the exception 

 of the part near the neck, and the spaces at the upper and lower angles occupied hy 

 the serratus magnus; (2) the lower two-thirds of the grooved outer border of the 

 scapula; and (8) the internuiscular sei)tum between it and the teres major. 



