316 THE MUSCULAR SYSTEM. 
facet on the great tuberosity of the humerus, and into the capsule of the shoulder 
joint. 
The muscle is entirely concealed from view by the trapezius, the acromion 
process, and the deltoid muscle. It covers the neck of the scapula, the supra- 
scapular vessels and nerves, and the upper surface of the capsule of the shoulder 
joint. 
The infraspinatus arises from the infraspinous fossa of the scapula (excepting a 
flat surface along the axillary border) and from the thick fascia over it. The fibres 
of the muscle converge to the neck of the humerus, separated from it by a bursa, 
and are inserted by tendon into the middle facet on the great tuberosity, and into 
the capsule of the shoulder joint. 
The lower part of the muscle is superficial. The upper part is hidden from 
view by the deltoid. Along its lower border is the teres minor. Near its 
insertion it crosses the neck of the scapula and the back of the capsule of the 
shoulder joint. 
The teres minor is a small muscle, arising from the upper two-thirds of the 
flat surface on the dorsal aspect of the axillary border of the scapula. Lying 
alongside the outer border of the infraspinatus, it is inserted under cover of the 
deltoid into the lowest of the three facets on the great tuberosity of the humerus, 
and into the capsule of the shoulder joint. It is separated from the teres major 
by the scapular head of the triceps, and by the posterior circumflex vessels and 
circumflex nerve. Its origin is pierced by the dorsal scapular artery. The muscle 
is invested by the deep fascia enclosing the infraspinatus, and is sometimes in- 
separable from that muscle. 
The teres major is much larger than the preceding muscle. It arises from 
the lower third of the flat surface on the dorsum of the scapula along its axillary 
border, except for a small area at the lower angle. The muscle is directed along 
the axillary border of the scapula to the front of the shaft of the humerus, where 
it is inserted into the inner border of the bicipital groove. It is closely adherent 
just before its insertion to the tendon of the latissimus dorsi muscle. 
The teres major is in close relation with the latissimus dorsi muscle, which 
conceals its origin posteriorly, winds round its outer border, and partially separates 
its anterior surface from the axillary vessels and nerves. The inner or upper 
border of the muscle is separated from the subscapularis and teres minor muscles 
by a quadrilateral interval containing the posterior circumflex vessels and the 
circuinflex nerve, and by a triangular interval containing the dorsal scapular artery, 
The long head of the triceps passes behind the teres major, and forms the boundary 
between these two spaces. 
The subscapularis is a large triangular muscle occupying the venter of the 
scapula. It arises from the whole of the subscapular fossa, except at the angles of the 
bone. Springing from several ridges in the fossa are septa projecting into the sub- 
stance of the muscle, which increase the extent of its attachment. Converging to 
the head of the humerus, the muscular fibres are inserted by tendon into the lesser 
tuberosity and into the capsule of the shoulder joint, under cover of the coraco- 
brachialis and short head of the biceps. This muscle forms the greater part of the 
posterior wall of the axilla. Its inner or anterior surface is in contact with the 
serratus magnus and the axillary vessels and nerves. Its deep surface is separated 
from the neck of the scapula by a bursa. Its upper border passes beneath the 
coracoid process ; its outer border is separated from the teres major by the cireum- 
flex vessels and nerve, the triceps muscle, and the dorsal scapular artery. 
_ _ The subscapularis minor is an occasional muscle situated below the capsule of the shoulder 
joint. It arises from the axillary border of the scapula beneath the subscapularis, and is inserted 
into the capsule of the joint or the upper part of the shaft of the humerus. 
NERVE SUPPLY. 
The muscles of this group are all supplied by the fifth and sixth cervical nerves, through the 
posterior cords of the brachial plexus. 
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