1414 



CLINICAL AND TOPOGRAPHICAL ANATOMY 



The shaft of the humerus is well covered by muscles in the greater part of its 

 extent, especially above. Below the insertion of the deltoid, the lateral border of 

 the bone can be traced downward into the lateral supracondyloid ridge. The 

 medial border and ridge are less prominent. 



Attached to these ridges and borders are the intermuscular septa, each lying between the 

 triceps and brachiahs (anterior), and the lateral one giving origin to the brachio-radialis (supi- 

 nator longus) and extensor carpi radialis longus as well. The medial extends up to the insertion 

 of the coraco-brachialis, the hiteral to that of the deltoid. The lateral septum is perforated by 

 the anterior part of the profunda vessels and the radial (musculo-spiral) nerve, the medial by the 

 superior and posterior branch of the inferior ulnar collateral (anastomotica magna) artery and 

 the ulnar nerve. 



The biceps has a two-fold attachment above and below. The former is of much importance 

 in steadj'ing the various movements, especially the upward one, and in harmonising the simul- 

 taneous flexion and extension of the shoulder- and elbow-joints. (Cleland.) The lacertus 

 fibrosus curving downward and medially with its semilunar edge upward, across the termina- 

 tion of the brachial artery, strengthens the deep fascia and the origin of the flexors of the fore- 

 arm. The two heads unite in the lower third of the arm. The tendon, before its insertion, 

 becomes twisted, the lateral border becoming anterior. 



Fig. 1132. — Cross-Section through the Middle of the Right Arm. (Heath.) 



Cephalic vein 



Musculo-cutaneous nerve 

 Brachialis 



Radial nerve 

 Profunda vessels 



Triceps, with fibrous intersection 



Biceps 



Brachial vessels 



Median nerve 

 Ulnar nerve 



Basilic vein, with internal 

 cutaneous nerves 



Superior ulnar collateral vessels 



On either side of the well-known prominence of the biceps is a furrow. Along 

 the lateral ascends the cephalic vein. The medial corresponds to the line of the 

 basilic vein which lies superficial to the deep fascia below the middle of the arm, 

 and superficial and medial to the brachial vessels and median nerve. 



The strength of such muscles as the deltoid, and their intimate connection with the peri- 

 osteum of tlie humerus, account for fracture of this bone by muscular action being more common 

 than elsevvher(!. The presence of muscular tissue between the fragments, together with de- 

 ficient immobilization, explains the fact that ununited fractures are also most common in the 

 liuriierus. The best incisions for exploring the humerus, e. g., in acute necrosis, etc., are (a) 

 for Ihc, i/{)/)er portion, the two already incut ioried .'iloug the anterior and posterior borders of the 

 deltoid. In the hitter case tlie presence of the radial (niusculo-sj)iral) nerve in the deeper part 

 of the wounrl must be remembered; (b) for the lower end one parallel with the lateralinter- 

 muscular .sei)tum, deepened between the brachialis and bracihio-radialis. 



A line drawn along the medial edge of the biceps from the insertion of the teres 

 major to the middle of the bend of the elbow corresponds to the brachial artery. 

 In the upper two-thirds, this artery can be compressed against the bone by pres- 

 sure laterally; in its low<!r third the humerus is behind it, and pressure should be 

 made backward. The jjresence of the median nerve will interfere with any pro- 

 longed digital pressure applied in the middle of the arm. 



