Part 39

Action.--Pulls the humerus inward (mediad).

=M. teres major= (Fig. 75, d; Fig. 77, c).--A thick muscle, triangular in cross-section, lying parallel with the glenoid border of the scapula.

Origin (Fig. 76, j; Fig. 78, b) from the vertebral one-third of the glenoid border of the scapula, and from fascia covering the subscapularis (Fig. 77, a) and the infraspinatus (Fig. 75, c) over a small area near the glenovertebral angle of the scapula. It may touch the insertion of the rhomboideus.

Insertion (Fig. 82, f) by a tendon common to it and the latissimus dorsi (Fig. 79, d′), as already described.

Relations.--Outer surface with the caput longum (Fig. 75, g) and the long portion (Fig. 80, f) of the caput mediale of the triceps, the latissimus dorsi (Fig. 77, e), and the cutaneus maximus. Inner surface with the serratus anterior (Fig. 73, i), the scalenus (Fig. 73, f), the transversus costarum (Fig. 73, j), and the biceps (Fig. 77, g). Dorsal border with the subscapularis (Fig. 77, a) and infraspinatus (Fig. 75, c).

Action.--Rotates the humerus inward and flexes it in opposition to the infraspinatus, teres minor, and the deltoidei.

a, M. subscapularis; b, M. teres major; c, M. serratus anterior; d, M. levator scapulæ; e, M. rhomboideus; f, M. occipitoscapularis; g, M. biceps; h, M. coracobrachialis; i, caput longum of M. triceps.]

2. =Muscles of the Brachium or Upper Arm.=

M. clavobrachialis and the pectoralis group (Fig. 65, page 109) lie partly in this region; they have been described.

=M. coracobrachialis= (Fig. 77, f; Fig. 79, c).--A very short muscle covering the inner (medial) surface of the capsule of the shoulder-joint. It extends from the coracoid process to the proximal end of the humerus.

Origin (Fig. 78, h).--By a round tendon from the tip of the coracoid process.

Insertion (Fig. 82, e) usually by fleshy fibres on an area five to eight millimeters long and about half as wide, which lies on the medial side of the humerus parallel with the ridge which runs from the dorsal end of the lesser tuberosity to the shaft and close to it. The proximal end of the area is about one centimeter from the proximal end of the head of the humerus.

Relations.--Medial surface with the biceps (Fig. 77, g), pectoralis minor (Fig. 65, o), and teres major (Fig. 77, c). Lateral surface with the capsule of the shoulder-joint. Dorsal border with the subscapularis (Fig. 77, a) and the long portion of the caput mediale of the triceps (Fig. 77, j).

Action.--Adducts the humerus.

The part of the coracobrachialis just described is known as the short head. A long head is sometimes found. It is a conical bundle of fibres of varying size, which arises from the tendon of origin of the short head. It passes distad into a long and extremely slender tendon, the insertion of which varies greatly in different individuals. It is commonly on the humerus in the region of the supracondyloid foramen.

=M. epitrochlearis= or extensor antibrachii longus (Fig. 65, r).--A thin, flat muscle on the inner or medial side of the brachium, from the lateral surface of the latissimus dorsi (Fig. 65, q) to the olecranon process of the ulna.

Origin from the lateral or outer surface of the ventral border of the latissimus dorsi (Fig. 65, q) near the insertion of the cutaneus maximus. Fibres are often attached to the teres major and the pectoralis minor.

Insertion by a flat tendon which is closely connected with that of the pectoantibrachialis (Fig. 65, m) and is continuous with the general antibrachial fascia, into the caudal border of the cutaneous (dorsal) surface of the olecranon process of the ulna.

Relations.--Outer (medial) surface with the integument, the latissimus dorsi (Fig. 65, q), and the cutaneus maximus. Inner (lateral) surface with the biceps (Fig. 65, t), caput longum (Fig. 65, s), and caput mediale (Fig. 77, j, k) of the triceps.

Action.--Extends the antibrachium and tends to supinate the hand by rotating the ulna.

=M. biceps brachii= (Fig. 77, g; Fig. 65, t).--A thick, fusiform muscle lying on the front (ventral) surface of the humerus.

Origin (Fig. 76, c) by a strong, round tendon from the bicipital tubercle of the glenoid angle of the scapula, at its coracoid margin. (In man there is a second head--coracoid head--from the coracoid process.) The tendon passes through the capsule of the joint and then along the bicipital groove, which is converted into a canal by a strong ligament.

Insertion by a rounded tendon (Fig. 87, b) on the bicipital tuberosity of the radius (Fig. 86, k).

Relations.--The tendon of origin passes through the capsule of the joint, which is covered by a part of the pectoralis minor. The muscle is then spanned for the middle part of its course by the bicipital arch (Fig. 65, t′), a description of which is given below. Farther distad it is covered by the clavobrachial (Fig. 65, k) and epitrochlearis (Fig. 65, r). At its distal end (Fig. 79, l′) the muscle passes between the pronator teres on the radial side and the conjoined tendon of the brachialis and clavobrachial (Fig. 79, i′) on the other. The biceps lies throughout most of its length on the ventral surface of the humerus, and touches along the medial border of its inner surface the coracobrachialis (Fig. 77, f), the teres major, (Fig. 77, c), the intermediate portion of the caput mediale of the triceps (Fig. 77, k), and the short portion (Fig. 77, l) of the same. Its lateral border touches the pectoralis minor (Fig. 65, o) and the brachialis (Fig. 79, i).

Action.--Flexes the forearm, and tends to supinate the hand.

=The bicipital arch= (Fig. 65, t′) is a tendinous arch formed over the biceps muscle. Its outer or lateral pillar is formed by the tendon of the pectoralis minor (o), to which may be added part of the latissimus (q) tendon. Its inner or medial pillar is formed by the conjoined tendon of the teres major and latissimus dorsi (Fig. 79, d′), while the xiphihumeralis (Fig. 65, p), cutaneus maximus (Fig. 62, b), and epitrochlearis (Fig. 65, r) are connected with one or the other pillar or with the muscles composing them. The caudal portion of the deep layer of the pectoralis major (Fig. 65, l) may be connected with the inner pillar.

=M. brachialis= (Fig. 79, i; Fig. 75, i).--From the lateral surface of the humerus to the ulna.

Origin (Fig. 83, g, g′) from a long V-shaped line two to four millimeters wide on the lateral surface of the humerus. The apex of the V is just distad of the teres minor tubercle (d). Its dorsal limb (g′) extends along the lateral supracondyloid ridge to a point opposite the proximal margin of the supracondyloid foramen; its ventral limb (g) extends in the direction of the deltoid ridge to the middle of the bone. No muscle-fibres take origin between the two limbs. The fibres converge and end in a flat tendon which joins the tendon of the clavobrachial (Fig. 79, k).