This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The biceps and brachialis anticus form the muscular mass on the anterior surface of the arm.
The biceps has no attachment to the humerus. It spans the bone and is attached to the scapula above and to the radius and deep fascia of the forearm below. In the lower half of the arm it lies on the brachialis anticus. The long head runs up in the bicipital groove, and is covered by the tendon of the pectoralis major up to the tuberosities, above that by the transverse humeral ligament up to the capsule, which it perforates, and, crossing over the head of the humerus, is attached to the upper edge of the rim of the glenoid cavity (Fig. 280).
The bicipital branch of the anterior circumflex artery accompanies the tendon in the bicipital groove. This tendon is comparatively rarely luxated, because it is firmly held in place by the transverse humeral ligament. Pus, in finding an exit from the joint, follows the long tendon of the biceps and passes under the transverse humeral ligament, then beneath the tendon of the pectoralis major to appear on the anterior aspect of the arm at its lower border. Luxation of the tendon outwardly would be opposed by the insertion of the pectoralis major, therefore it is only displaced inwardly. Rupture of the long tendon may occur from violent muscular contraction; or, in rheumatoid arthritis of the shoulder, the tendon may become partly dissolved and break. When this occurs the belly of the muscle contracts and forms a large protuberance on the front of the arm (Fig. 281).
The short head of the biceps fuses with the coracobrachialis muscle, to be attached with it to the coracoid process on its outer portion. The pectoralis minor is the third muscle attached to this process. The biceps forms the large muscular swell on the front of the arm between the anterior fold of the axilla and elbow. At its lower end the biceps inserts by a strong tendon into the posterior border of the bicipital tubercle of the radius. An example of its rupture is shown in Fig. 282. Between it and the bone is a bursa, which does not communicate with the elbow-joint. The bicipital fascia is given off from the tendon and passes downward and inward to blend with the deep fascia covering the flexor group of muscles. The biceps not only flexes the radius on the arm but also acts as a powerful supinator.
The brachialis anticus covers the lower three-fifths of the humerus and begins with two slips, one on each side of the insertion of the deltoid tendon. It inserts into the inner and lower part of the anterior surface of the coro-noid process of the ulna. As the articulation of the ulna and trochlear surface of the humerus is a pure hinge-joint the muscle acts solely as a flexor.