28o HUMAN ANATOMY. 



the head of the bone and the under surface of the acromion and coraco-acromial 

 ligament. 



When suppuration occurs, pus may find its way out from the joint, (i) By 

 following the bicipital tendon and opening on the arm below the anterior border of 

 the axilla. (2) By following the subscapular tendon, getting between that muscle 

 and the body of the scapula, and opening beneath and behind the axilla. (3) By 

 penetrating the capsule beneath the deltoid, when the dense deltoid and infraspinous 

 fascia prevent it from going backward and direct it to the anterior aspect of the 

 arm. Treves mentions a case in which it followed the course of the musculo-spiral 

 nerve and appeared on the outer side of the elbow. 



Landmarks. — The edge of the acromion and the tip of the coracoid can 

 readily be felt, though the coraco-acromial ligament completing the important arch 

 above the joint is beneath the deltoid, and therefore cannot be so distinctly pal- 

 pated, but can usually be recognized by' touch. An incision through the centre 

 of this ligament would open the shoulder-joint where the bicipital tendon enters 

 its groove. The head of the bone, when pressed upward against this arch, com- 

 municates motion to the outer fragment in cases of fractured clavicle, and this is 

 often the easiest way in that lesion of eliciting crepitus and preternatural mobility. 

 In cases of paresis or paralysis of the deltoid, the resultant atrophy may leave the 

 whole arch palpable, or even visible, in some instances the bone dropping from one 

 to several inches. 



The lower margin of the glenoid cup and the head of the humerus may be felt 

 in the axilla when the arm is abducted (Fig. 293). 



The greater tuberosity may be felt through the deltoid, directly beneath the 

 acromion, the arm hanging at the side. It faces in the direction of the external 

 condyle. Together with the lesser tuberosity it produces the normal roundness of 

 the deltoid. 



The head of the bone cannot be felt externally. It faces in the general direction 

 of the internal condyle. Two-thirds of it, when the arm is by the side, is in front 

 of a vertical line drawn from the anterior border of the acromion process. It is also 

 altogether external to the coracoid process. 



The lesser tuberosity faces forward. Between it and the greater tuberosity, 

 when the arm is hanging loosely and is supine, the lower part of the bicipital groove 

 may be felt in thin subjects. This also faces directly forward, and is on a line drawn 

 through the middle of the biceps and its lower tendon. 



The upper part of the humeral shaft cannot be felt. The circumflex nerve winds 

 around it a little above the middle of the deltoid. The deltoid tubercle may be 

 recognized at the middle of the arm. From there downward the bone is more 

 superficial externally, and the outer supracondylar ridge may be traced down to the 

 condyle. The less prominent internal ridge can be felt only for a short distance 

 above the elbow. 



The middle of the humerus, indicated by the insertion of the deltoid on the 

 outer side, is also on a level with that of the coraco-brachialis on the inner and with 

 the upper portion of the brachialis anticus on the anterior surface, with the origin 

 of the nutrient and inferior profunda arteries, with the exit through the deep fascia 

 of the nerve of Wrisberg and the entrance of the basilic vein, with the passage of 

 the 'median nerve across the brachial artery, and with the departure of the ulnar 

 nerve from its proximity to the vessel. Posteriorly, the middle of the bone is covered 

 by the triceps. 



Just below the middle the musculo-spiral nerve and the superior profunda wind 

 around in the groove below the deltoid insertion, and the inner head of the triceps 

 arises from the bone. 



At the junction of the middle and lower thirds the brachial artery from the 

 inner side and the musculo-spiral nerve from the outer side tend to approach the 

 front of the bone. 



The landmarks at the lower extremity will be considered in relation to the 

 elbow-joint and the bones of the forearm. 



The surface anatomy and the relations of the soft parts to the humerus will be 

 recurred to after those structures have been described. 



