480 BONES AND MUSCLES OF UPPER EXTREMITY. 



muscles which move it are for the most part attached to its upper 

 third ; and the chief of them are the pectoralis major (fig. 227, 

 2 , 3 ) which rises from the sternum and cartilages of the ribs, 

 and consequently draws the arm forwards, inwards, and down- 

 wards, the latissimus dorsi (fig. 226, 9 ), which rises from the 

 spinal column and hinder part of the ribs, and consequently 

 draws the arm backwards, inwards, and downwards, and the 

 deltoid (fig. 226, 5 ), which arises from the upper edge of the 

 clavicle, and from the ridge of the scapula, and is the chief 

 muscle concerned in raising the arm. The first of these forms 

 the principal part of the fleshy mass upon the front of the 

 chest, and is the muscle which is so remarkably developed in 

 Birds. It forms also the front boundary of the axillary space, 

 or hollow of the arm-pit, the hinder boundary of which is 

 formed by the second muscle. This space, of which we can 

 distinctly feel the front and back walls when we raise the 

 arm a little from the side, contains the large vessels and 

 nerves proceeding to the arm, and also a number of lymphatic 

 glands ( 219). The deltoid muscle forms the thick fleshy 

 mass on the top of the shoulder and on the upper part of the 

 outside of the arm. 



639. In the fore-arm of Man there are two long bones, 

 termed the Radius and the Ulna, which lie nearly parallel to 

 each other ; the radius being on the outer or thumb side of the 

 fore-arm, and the ulna on the inner. They are connected 

 with one another, not only by ligaments at their extremities, 

 but by a strong fibrous membrane that passes between their 

 adjacent edges, along their entire length. Nevertheless they 

 have considerable freedom of motion, not only upon the 

 humerus, but upon each other; so as to give to the fore -arm 

 the power of rotation on its own axis, by which either the 

 palm or the back of the hand may be turned upwards. The 

 ulna is connected with the humerus, at the elbow, by means 

 of a hinge-joint, into which the radius does not enter ; but it 

 is the radius with which the hand is connected at the wrist, 

 by a kind of ball-and-socket joint, the ulna having no direct 

 share in this articulation : hence, while both bones move 

 together in bending or straightening the elbow, we can make 

 the radius roll round the ulna, carrying the hand with it. 

 This movement is one of very great importance, in rendering 

 the hand capable of a great variety of uses to which it would 



