252 DISSECTION OF THE ARM. 



MUSCLES ON THE FRONT OF THE ARM. There are only throe muscles 

 on the tore part of the arm. The one along the centre of the limb is the 

 biceps ; and that along its inner side, reaching about half way down, is 

 the coraco-brachialis. The brachialis anticus lies beneath the biceps. 

 Some muscles of the forearm are connected to the inner and outer condyles 

 of the humerus, and to the line above the outer condyle. 



The BICEPS MUSCLE (fig. 78, B ) forms the prominence observable on 

 the front of the arm. It is wider at the middle than at either end; and 

 the upper part consists of two tendinous pieces of different lengths, which 

 are attached to the scapula. The short head arises from the apex of the 

 coracoid process in common with the coraco-brachialis muscle (fig. 73) ; 

 and the long head is attached to the upper part of the glenoid cavity of 

 the scapula, within the capsule of the shoulder joint (fig. 89). Muscular 

 fibres spring from each tendinous head, and blend about the middle of the 

 arm in a fleshy belly, which is somewhat flattened from before back. In- 

 feriorly the biceps ends in a tendon, and is inserted into the tubercle of 

 the radius. 



The muscle is superficial except at the extremities. At the upper part 

 it is concealed by the pectoralis major and deltoid muscles; and at the 

 lower end the tendon dips into the hollow in front of the elbow, having 

 previously given an offset to the fascia of the arm. Beneath the biceps 

 are the brachialis anticus muscle, the musculo-cutaneous nerve, and the 

 upper part of the humerus. Its inner border is the guide to the brachial 

 artery below the middle of the humerus, but above that spot the coraco- 

 brachialis muscle intervenes between them. The connection of the long 

 head of the biceps with the shoulder joint, and the insertion of the muscle 

 into the radius, will be afterwards learnt. 



Action. It bends the elbow-joint, and acts powerfully in supinating 

 the radius. When the body is hanging by the hands it will apply the 

 scapula firmly to the humerus, and will assist in raising the trunk. 



With the arm hanging and the radius fixed, the long head w r ill assist 

 the abductors in removing the limb from the thorax ; and after the limb 

 is abducted, the short head will aid in restoring it to the pendent position. 



The CORACO-BRACHIALIS (fig. 73, H ) is roundish in form, and is named 

 from its attachments. Its origin is fleshy from the tip of the coracoid 

 process, and from the tendinous short head of the biceps. Its fibres be- 

 come tendinous, and are inserted, below the level of the deltoid muscle, 

 into the ridge on the inner side of the humerus : from the insertion an 

 aponeurotic slip is continued upwards to the head of the humerus, and is 

 joined by fleshy fibres. 



Part of the muscle is beneath the pectoralis major (fig. 78), and forms 

 a prominence in the axilla; but the rest is superficial, except at the inser- 

 tion where it is covered by the brachial vessels and the median nerve. 

 The coraco-brachialis conceals the subscapular muscle, the anterior cir- 

 cumflex artery, and the tendons of the latissimus and teres. Along the 

 inner border are the large artery and nerves of the limb. Perforating it 

 is the musculo-cutaneous nerve. 



Action. The hanging limb is adducted to the thorax by this muscle; 

 and the action is greater in proportion as the humerus is removed from 

 the trunk. 



The humerus being fixed, the muscle will bring down the scapula, and 

 assist in keeping the articular surfaces of the shoulder joint in apposition. 



