Action.—Flexes the humerus and rotates it outward.
M. acromiodeltoideus ([Fig. 75], f; [Fig. 68], g).—A flat muscle which overlies the distal end of the spinodeltoideus ([Fig. 75], c). It connects the acromion with the humerus.
Origin ([Fig. 76], d).—From the glenoid border of the acromion, and sometimes the adjacent metacromion as far as the tip.
Insertion.—Mostly upon the outer surface of the spinodeltoideus ([Fig. 75], c). The outer fibres are continued to the bone, especially at the lateral border of the muscle, and are inserted along a line ventrad of the line of insertion of the spinodeltoideus, and extending farther distally ([Fig. 81], g). Some of the outer fibres pass into the brachialis ([Fig. 80], h).
Relations.—Outer surface with the integument and the clavobrachial ([Fig. 68], e). Inner surface with the infraspinatus ([Fig. 75], c), teres minor ([Fig. 80], c), spinodeltoid ([Fig. 75], e), and caput laterale of the triceps ([Fig. 75], h).
Action.—Like that of the spinodeltoid.
M. clavobrachialis ([Fig. 65], k; [Fig. 68], e).—A flat, triangular muscle on the cranial surface of the shoulder, forming a direct continuation of the clavotrapezius ([Fig. 68], d). These two are frequently described as constituting a single muscle, the cephalohumeral or cephalobrachial. (The clavobrachial is frequently given the name clavodeltoid; as its homology with the human clavodeltoid appears doubtful, it seems well to use the name clavobrachial, as proposed by Clasen.)
[Fig. 75].—Muscles on the Lateral Surface of the Arm.
![[Fig. 75]](#3418956513767812439_illo158lg.jpg.id-960289891847406759.wrap-0.html.html){kind=link}
a, M. supraspinatus; b, part of insertion of M. rhomboideus; c, M. infraspinatus; d, M. teres major; e, M. spinodeltoideus; f, M. acromiodeltoideus; g, caput longum of M. triceps brachii; h, caput laterale of M. triceps brachii; i, M. brachialis; j, M. biceps; k, M. brachioradialis; l, M. extensor carpi radialis longus; m, M. extensor communis digitorum (m′, tendon of same); n, M. extensor lateralis digitorum; (n′, tendon of same); o, M. extensor carpi ulnaris (o′, tendon of same); p, M. extensor indicis proprius; q, fifth head of M. flexor profundus digitorum; r, M. flexor carpi ulnaris. 1, vertebral border of the scapula; 2, spine of the scapula; 3, greater tuberosity of the humerus; 4, olecranon; 5, transverse ligament of the wrist.
