3 io APPLIED ANATOMY. 



as to extend it, and, being attached to the humerus above the line of the elbow- 

 joint, it also aids in flexing the elbow. 



Extensor Carpi Radialis Brevier. The extensor carpi radialis brevior 

 arises from the common tendon of the lateral condyle and fascia, and, running 

 down parallel to the longior muscle, inserts into the base of the third metacarpal 

 bone. It is covered by the extensor carpi radialis longior muscle and lies on the 

 supinator (brevis). It acts as a pure extensor of the wrist (Fig. 325). 



Extensor Carpi Ulnaris. The extensor carpi ulnaris arises by two heads, 

 one from the lateral (external) condyle and the other from the posterior surface of 

 the ulna through the fascia common to it, to the flexor carpi ulnaris, and to the flexor 

 profundus digitorum. It inserts into the base of the fifth metacarpal bone. It extends 

 the wrist and tilts the hand toward the ulnar side. 



3. PRONATORS AND SUPINATORS OF THE HAND. 



The movements of pronation and supination have already been described 

 (page 304). They are performed by five muscles, two pronators and three supin- 

 ators. The pronators are the pronator radii teres and the pronator quadratus. 

 The supinators are the brachioradialis {supinator longus}, the supinator {brevis}, 

 and the biceps. 



PRONATORS OF THE HAND. 



Pronator Radii Teres (Round Pronator). The pronator radii teres arises 

 by two heads, one from the medial (internal) condyle and the other, much smaller, 

 from the inner surface of the coronoid process. The median nerve passes between 

 these two heads. The muscle crosses the forearm obliquely and inserts by a flat 

 tendon into the middle of the outer surface of the radius. It rotates the radius 

 inward and tends to draw it toward the ulna and flex it on the humerus. The 

 influence of this muscle is marked in displacing the radius when fractured. 



Pronator Quadratus (Square Pronator}. The pronator quadratus arises 

 from the volar (palmar) surface of the lower fourth of the ulna and inserts into the 

 lateral and anterior surface of the radius. By its contraction it rotates the radius 

 toward the ulna and in cases of fracture tends to draw the bones together and thus 

 endanger the integrity of the interosseous space (Fig. 326). 



SUPINATORS OF THE HAND. 



Brachioradialis (Supinator Longus}. The brachioradialis arises from the 

 upper two-thirds of the lateral (external) supracondylar ridge of the humerus and 

 inserts into the base of the styloid process of the radius. When the hand is in a state 

 of pronation contraction of the brachioradialis will tend to supinate it. It also acts 

 as a flexor of the elbow, as has already been pointed out. It is superficial and is an 

 important guide both to the radial (musculospiral) nerve and to the radial artery. 



Supinator (Brevis}. The supinator arises from the lateral condyle, the 

 external lateral and orbicular ligaments, and the triangular surface of the ulna 

 below the lesser sigmoid cavity. It winds around the posterior and external sur- 

 faces of the radius and inserts into the upper and outer portion, covering its head, 

 neck, and shaft as low down as the insertion of the pronator radii teres muscle. 

 It lies deep down beneath the mass of extensor muscles and supinates the radius. 

 It is pierced by the deep branch of the radial (posterior interosseous) nerve which 

 bears the same relation to it as does the external popliteal nerve to the peroneus 

 longus muscle in the leg. 



Biceps Muscle. The biceps muscle has already been described. Arising 

 by its long head from the upper edge of the glenoid cavity and by its short head 

 from the coracoid process it inserts into the posterior portion of the tubercle of 

 the radius. While its main function is that of flexion of the elbow, still, from the 

 manner in which it winds around the tubercle of the radius, it acts as a powerful 

 supinator when the hand is prone and it is a disturbing factor in the displacements 

 which occur in fractures of the bones of the forearm. 



