212 MUSCLES OF THE UPPER LIMB. 



Posteriorly this muscle is covered at its lower part by the latissimus dorsi, and at 

 its upper part it is crossed by the long head of the triceps. The outer side is sur- 

 rounded by the latissimus dorsi ; and the anterior surface is concealed in the upper 

 part of its extent by the tendon of that muscle. The inner border of the muscle 

 forms the other margin of a triangular space, of which the other sides are the upper 

 part of the humerus, and the axillary border of the scapula covered before and 

 behind by the subscapular and teres minor muscles; this triangle is divided by 

 the long head of the triceps into a superior or external quadrilateral, and an inferior 

 or internal triangular compartment. Through the quadrilateral space pass back- 

 wards the posterior circumflex vessels and the circumflex nerve ; and in the trian- 

 gular subdivision the dorsal branch of the subscapular artery passes round the margin 

 of the scapula into the infraspinous fossa. The scapular slip of the latissimus dorsi 

 arises in connection with the teres major. 



ACTIONS. The deltoid muscle raises the arm from the side as far as the structure 

 of the shoulder-joint permits : that is, till it is at right angles with the trunk. 

 Further elevation of the upper limb is effected chiefly by the trapezius ; and it 

 may be remarked, that the insertion of that muscle corresponds exactly in extent 

 to the origin of the deltoid, so that the two muscles may be considered continuous 

 in structure and in action. The anterior fibres of the deltoid combine with the pecto- 

 ralis major to draw the humerus forwards ; the posterior assist in drawing it back- 

 wards. The supraspinatus, infraspinatus, and subscapularis muscles being placed 

 more closely round the joint, when acting in concert with the deltoid probably 

 give steadiness and precision, while the deltoid gives the main elevating force to 

 the movement. The supraspinatus simply elevates : the infraspinatus and sub- 

 scapularis carry the arm backwards or forwards when it is raised, and rotate it 

 outwards or inwards when hanging by the side. The teres major rotates the 

 raised humerus inwards, the teres minor outwards : acting together, they assist in 

 depressing the arm. 



MUSCLES OF THE ARM. 



The coraco-brachialis muscle, elongated in form, arises from the tip of the 

 coracoid process of the scapula, between the pectoralis minor and the short 

 head of the biceps, with which latter it is for a short distance conjoined. 

 It is inserted into the inner border of the humerus near its middle, in a 

 linear impression of from two to three inches in length, between the origin 

 of the triceps and the brachialis anticus. From its insertion a tendinous 

 offset is prolonged upwards to the head of the humerus. 



This muscle is usually pierced by the musculo-cutaneous nerve ; its outer border is 

 in contact with the biceps muscle, and its inner with the brachial artery, by which it 

 is crossed obliquely near its insertion. It lies in front of the tendons of the subscapu- 

 laris, latissimus dorsi and teres major, and is covered by the deltoid and pectoralis 

 major muscles. 



The Uceps flexor cubiti muscle has two heads of origin of unequal length : 

 one of these, the internal or short head, arises conjointly with the coraco- 

 brachialis from the coracoid process of the scapula by a tendon which is 

 soon continued into muscle; the other, the long head, arises by a cylindrical 

 tendon from the upper border of the glenoid ligament, within the capsule 

 of the shoulder- joint, and this tendon, passing over the head of the humerus, 

 leaves the joint by the bicipital groove, and gradually enlarges into the fleshy 

 head as it descends. The muscular fibres from those two heads, lying side 

 by side, unite to form an elongated and thick belly, occupying the middle 

 and lower part of the arm : the muscle then suddenly becoming narrower 

 a little above the bend of the elbow, is continued into the flat rounded 



