404 JAMES CRAWFORD WATT 



Inserlioti. Runs directly parallel to radius and inserts at the 

 middle of the shaft of that bone, just medial (owing to pronation 

 apparently lateral) to the brachioradialis. 



This muscle probably represents the undifferentiated remainder 

 of the superficial extensor mass, except the extensor carpi ul- 

 naris which is separate. It will thus include the extensors carpi 

 radialis longus and brevis, digitorum communis and digiti quinti 

 proprius. In some reptilia and amphibia these muscles are in a 

 common supinato-extensor mass. 



Why none of this mass reaches the carpus or digit cannot 

 be explained, but the fact that none of it does so explains why 

 the hand is carried in a position of permanent flexion, because 

 there is a flexor muscle attached to the digit and it is thus 

 without an opponent to its pull. 



3. Supinator (figs. 8 and 10, A.) 



Origin. Covered by the common extensor mass it comes from 

 the anterior surface of the lateral condyle of the humerus. 

 This represents the superficial or humeral portion only of the 

 normal human muscle. 



Insertion. It courses parallel and deep to the common exten- 

 sor mass and is inserted into the capsule of the radio-humeral 

 joint, head, neck and upper third of the shaft of the radius, 

 right down to the insertion of the common extensor mass. 



This muscle, it seems to me, is quite evidently the supinator, 

 and so is the single representative here of the deep muscles of 

 the extensor series in the forearm. 



Extensor carpi ulnaris (figs. 7, 8, 9 and 10, E.C.U.) 



Origin. Below the preceding muscle from the lowest part of 

 the lateral epicondyle of the humerus. This is the last of the ex- 

 tensor group and lies in contact with the flexors. It is the 

 longest of the extensors, being over double the length of any of 

 the others. 



Insertion. By a long slender tendon which is one-third the 

 length of the muscle, into the middle of the dorsal surface at the 



