108 ANATOMY AND PHYSIOLOGY 



Extensor carpi radialis longus, or long radial extensor of the 

 wrist. Origin. Lateral border and epicondyle of humerus. 

 Insertion. The base of the second metacarpal bone. 



Nerve. Radial. 



Extensor carpi radialis brevis, or short radial extensor. Origin. 

 The lateral epicondyle. Insertion. The base of the third 

 metacarpal bone. 



Nerve. Deep branch of radial. 



Extensor carpi ulnaris, or ulnar extensor of the wrist. Origin. 

 -The lateral epicondyle and dorsal border of the ulna. Inser- 

 tion. The base of the fifth metacarpal bone. 

 Action of the three. They extend the wrist. 



Nerve. Deep branch of radial. 



Extensor digitorum communis, or common extensor of the 

 fingers. Origin. The lateral epicondyle. Insertion. By four 

 tendons, on the second and third rows of phalanges, in such a way 

 that it can extend the bones of either row separately or both at the 

 same time. 



The little finger has a special extensor for its tip (extensor minimi digiti). 

 The index finger also has a special extensor (extensor indicis), and the thumb 

 has three two for its phalanges, and one for its metacarpal bone. By forci- 

 bly extending the thumb these three tendons are brought into view, the one for 

 the tip of the thumb being at a little distance from the other two; thus they 

 bound a little hollow which has been called the "anatomic snuff box." 



Nerves of all. Deep branch of radial. 



THE Two SUPINATORS 



The supinator. Origin. The lateral epicondyle and upper 

 end of the shaft of the ulna. It winds around the head and neck 

 of the radius to the insertion on upper part of the shaft. This is 

 the chief supinator; it is entirely covered -by other muscles. 



Action. It rotates the radius and turns the dorsum of the 

 hand downward or backward. 



Nerve. Deep branch of radial. 



The branchio-radialis (Fig. 87). Origin. The lateral border 

 of the humerus. Insertion. The styloid process of the radius. 



