Action of the Triceps.—The entire triceps group forms a powerful extensor of the forearm. The short portion of the medial head tends also to rotate the arm outward, so as to supinate the hand.
M. anconeus ([Fig. 80], l).—A triangular muscle on the outside of the elbow-joint from the humerus to the ulna.
Origin ([Fig. 83], i).—An irregularly triangular area at the distal end of the dorsal surface of the humerus. The area of origin is limited laterally by the sharp lateral supracondyloid ridge. It sometimes extends onto the lateral epicondyle.
[Fig. 81].—Ventral Surface of Humerus, with the Areas of Attachment of Muscles.
![[Fig. 81]](#3418956513767812439_illo171alg.jpg.id-1226556237569565593.wrap-0.html.html){kind=link}
[Fig. 82].—Medial Side of Humerus, with the Areas of Attachment of Muscles.
![[Fig. 82]](#3418956513767812439_illo171blg.jpg.id-2868775378538744121.wrap-0.html.html){kind=link}
[Fig. 83].—Dorsal Surface of the Left Humerus, with the Areas of Attachment of Muscles.
![[Fig. 83]](#3418956513767812439_illo171clg.jpg.id-1019665360846536095.wrap-0.html.html){kind=link}
Fig. 81.—a, M. subscapularis; b, M. supraspinatus; c, Mm. teres major and latissimus dorsi; d, M. pectoralis minor; e, deep layer of M. pectoralis major; f, superficial layer of M. pectoralis major; g, M. acromiodeltoideus; h, M. spinodeltoideus; h′, caput laterale of M. triceps; i, M. brachialis; j, second portion of M. brachialis; k, M. extensor carpi radialis longus; l, M. extensor carpi radialis brevis; m. M. extensor communis digitorum; n, M. extensor lateralis digitorum; o, M. extensor carpi ulnaris; p, short portion of caput mediale of M. triceps; q, M. pronator teres; r, M. palmaris longus; s, third and fourth parts of M. flexor profundus digitorum; t, M. flexor carpi radialis; u, second head of M. flexor profundus digitorum.