THE FOREARM 



1419 



THE FOREARM 



Bony landmarks. — The posterior border of the ulna can be easily traced down 

 from the olecranon to the back of the styloid process; the bone becomes somewhat 

 rounded below, and lies between the flexor and extensor carpi ulnaris. The tip of 

 the styloid process corresponds to the medial end of the line of the wrist-joint. The 

 radius is covered above by the brachio-radialis and radial extensors of the carpus, 

 and the outline of the bone is less easily followed. Its styloid process is readily 

 made out below a finger 's breadth above the thenar eminence. It is placed about 

 1.2 cm. (I in.) lower than that of the styloid process of the ulna. 



Thus, a line drawn straight between the two processes would fall a little below that of the 

 wrist-joint, this being shown by a line drawn between the two processes forming a slight curve, 

 with its concavity downward (corresponding to the concavity of the lower surface of the radius 

 and fibro-cartilage) about 1.2 cm. (5 in.) above the straight line given above. 



The radial styloid process is covered by the abductor longus and extensor brevis pollicis, 

 while farther out lies the extensor pollicis longus. Between the styloid process of the ulna and 



Fig. 1137. — The Brachial Artery at the Bend of the Elbow. 

 (From a mounted specimen in the Anatomical Department of Trinity College, Dublin.) 



Posterior branch of medial 



antibrachial cutaneous 



nerve 

 Anterior branch of medial 



antibrachial cutaneous 



nerve 



Brachial artery 



Branch to pronator teres 

 Lacertus fibrosus, cut 



Pronator teres muscle 



Median nerve 



Ulnar artery 



Biceps muscle 



Branch of radial nerve tc 

 supinator longus 



Superficial radial nerve 



Radial recurrent artery and 

 deep radial nerve 



•] Tendon of biceps 



Musculo-cutaneous nerve 



Brachio-radialis muscle 



Radial artery 



the rounded head is the groove for the extensor carpi ulnaris. The bones are nearest to each 

 other in complete pronation, and farthest apart in complete supination. On section, the bones 

 are found at every point nearer to the back than to the front of the limb, but increasingly so 

 above. 'The lower the section proceeds down the Umb, the less will the bones be covered at the 

 sides, and the more equally will the soft parts be distributed about the anterior and posterior 

 aspects of the limb. It will be noticed that where one bone is the more substantial, the other 

 is the more slender, as near the elbow and wrist; and that it is about the centre of the limb 

 that the two are most nearly of equal strength.' (Treves.) When the limb is pronated, the 

 interosseous space is narrowed; in supination and the mid-position it is widened out. In 

 pronation, both styloid processes can be distinctly made out; in supination, that of the radius 

 is the more distinct, as now the skin and soft parts are stretched and raised over that of the ulna. 



Joints. — The position of the superior radio-ulnar joint is marked by a dimple 

 about 12 mm. (| in.) below the lateral epicondyle. The inferior can just be felt, 



