74 Anatomy Applied io Medicine and Swgery. 



surface of the humerus and inside bt the orbicular liga- 

 ment which binds it to the ulna. The tendon at its 

 insertion into the tuberosity is so twisted that its external 

 border is applied higher up on the bone than its in- 

 ternal border and its anterior surface is in contact with 

 the front part of the tuberosity. 2. Theptonator radii 

 teres, arising from the humerus above the internal con- 

 dyle by one head , and from the inner border of the coron- 

 oid process by the other, and inserted into the middle 

 of the outer surface of the shaft of the radius, flexes the 

 forearm, and, passing as it does from the inner aspect of 

 the forearm to the outer side of the radius, rolls the 

 radius inwards an action the direct opposite to that of 

 the biceps. Hence the biceps supi nates, and the pro- 

 nator radii teres pronates the forearm. 3. Supinator longus, 

 rom the upper two- thirds of the supracondyloid ridge of the 

 humerus, into the forepart of the outer side of the base of 

 the styloid process of the radius, supinates this bone and, 

 therefore, the forearm, when it has already been pronated, 

 or pronates it, when it has been supinated, i.e., it assists 

 in maintaining the forearm in a position midway between 

 pronation and supination, as when placed across the 

 chest. 4. The supinator brevis, from the external condyle 

 of the humerus, the external ligament of the joint and 

 from the ulna into the neck and oblique line of the radius, 

 is also a supinator of the radius. 5. The anconeus, from 

 the back part of the outer condyle, into the side of the 

 olecranon and upper one-fourth of the posterior surface of 

 the ulna, assists the triceps in extending the arm. The 

 pronator quad-tatus, from the lower one-fourth of the ante- 

 rior surface of one bone into the corresponding surface of the 

 other, tends to pull the bones together, but, since the ulna 

 is fixed by its interlocking with the humerus above, the 

 radius alone can move, which it does, in the form of rota- 



