398 



THE MUSCLES AND FASCIAE. 



The Supinator brevis (Fig. 236) is a broad muscle, of hollow cylindrical form, 

 curved round the upper third of the radius. It consists of two distinct planes of 

 muscular fibres, between which lies 

 the posterior interosseous nerve. The 

 two planes arise in common : the 

 superficial one by tendinous, and the 

 deeper by muscular, fibres from the 

 external condyle of the humerus ; 

 from the external lateral ligament 

 of the elbow-joint and the orbicular 

 ligament of the radius ; from the 

 ridge on the ulna, which runs ob- 

 liquely downward from the posterior 

 extremity of the lesser sigmoid cav- 

 ity ; from the triangular depression 

 in front of it ; and from a tendinous 

 expansion which covers the sur- 

 face of the muscle. The superficial 

 fibres surround the upper part of 



Int. 

 Condyle. 



Olecranon. 



Coronoid" 



proc. 

 Head of 



radius. 



TENDON 

 BICEPS. 



FIG. 236. Supinator brevis. (From a prepara- 

 tion in the Museum of the Royal College of 

 Surgeons of England.) 



EXTENSOR 

 CARPI ULNARIS, 



FIG. 237. Posterior surface of the forearm. l>eep muscles. 



the radius, and are inserted into the outer edge of the bicipital tuberosity 

 and to the oblique line of the radius, as low down as the insertion of the 

 Pronator radii teres. The upper fibres of the deeper plane form a sling-like 

 fasciculus, which encircles the neck of the radius above the tuberosity and is 



