UPPER EXTREMITY AND THORAX, ANTERIOR. 257 



By raising the arm half way to a right angle from the 

 body, the anterior and posterior boundaries of the axillary 

 space will appear, the pectoralis major in front and the 

 latissimus dorsi behind. Between them is the cavity of the 

 axilla. By carrying the ringers high up in this cavity the 

 head of the humerus can be felt. 



The line of the axillary artery : Extend the arm until it 

 is at right angles with the trunk, then draw a line from the 

 middle of the clavicle to the depression at the inner border 

 of the coracobrachialis and biceps muscles. 



The pectoral border leads down to the fifth rib. 



To count the ribs, remember that the second rib joins 

 the sternum (through its cartilage) at the articulation be- 

 tween the first and second pieces of the sternum ; that the 

 seventh at the junction of the second and third parts of the 

 sternum ; that the fourth rib is just above, and the fifth 

 just below the nipple; that the tenth, eleventh, and 

 twelfth can be located by touch along the lower border 

 of the thorax. 



The arm presents a prominence in front due to the bi- 

 ceps muscle, and a slight depression at its outer and inner 

 margins ; in the outer lies the cephalic vein and in the inner 

 the brachial artery, and veins with the median nerve. The 

 inner margin of the muscle is the guide to the artery. A 

 similar prominence is upon the back of the arm, formed by 

 the triceps muscle. 



At the elbow recognize the two (epi) condyles of the 

 humerus, the olecranon process of the ulna, and the head 

 and tuberosity of the radius. The internal (epi) condyle, 

 being more prominent than the external, is more often 

 broken off than the external. It points in the direction to 

 which the head of the humerus faces. 



The prominent olecranon behind bears certain relations 

 17 



