MYOLOGY. 67 



The muscles situated on the outer and back part of the forearm ai'e 

 supinators and extensors, and may, like the last set, be arranged in a super- 

 ficial and a deep layer. The superficial consists of seven : supinator radii 

 longus, extensor carpi radialis longus and hrevis^ extensor digitorum communis, 

 extensor minimi digiti, extensor carpi ulnaris, and anconceiis. The deep mus- 

 cles are five : the supinator radii brevis, three extensors of the thumb, and 

 the indicator. 



/Supinator radii longus, forming the prominence along the outer and ante- 

 rior part of the forearm, arises from the external ridge of the humerus, and 

 from the intermuscular ligament separating it from the outer head of the 

 triceps. It is inserted into a rough surface on the outside of the radius, near 

 its styloid process. It serves to roll the radius backwards and to bend the 

 elbow joint. 



Extensor carpi radialis longus arises from the ridge on the external side of 

 the humerus, and is inserted into the back part of the metacarpal bone of 

 the index finger. 



Eciensor carpi radialis brevis arises from the inferior and posterior part of 

 the external condyle, and from the external lateral ligament ; it is inserted 

 into the carpal extremity of the third metacarpal bone (that of the middle 

 finger). 



Extensor digitorum communis arises with the last and the extensor minimi 

 digiti, from the external condyle and from the ulna. About the middle 

 of the back of the forearm it ends in four muscles, each endino^ in tendon;^, 

 which pass under the annular ligament and are inserted into the phalanges 

 of the four fingers. It serves to extend all the joints of the fingers, as also 

 the carpus. 



Extensor carpi ulnaris arises from the external condyle, fascia, and inter- 

 muscular septa, and ends in a strong tendon, which is inserted into the 

 carpal end of the fifth metacarpal bone. It extends and bends back the 

 hand, and adducts or flexes it laterally towards the ulna. 



Anconceus is placed at the outer side of the olecranon, beneath the skin, 

 and arises from the posterior and inferior part of the external condyle and 

 lateral ligament, and is inserted into the external surface of the olecranon, 

 and the superior fifth of the posterior surface of the ulna. Its use is to 

 extend the forearm on the arm. 



Extensor minimi digiti vel auricidaris arises in common with the extensor 

 communis, and is inserted with the fourth tendon of this muscle into the 

 posterior part of the phalanges of the little finger. It assists the extensor 

 communis, and can extend and abduct the little finger independently of the 

 rest. 



Supinator radii brevis surrounds the upper part of the radius : it arises 

 from the external condyle, external, lateral, and coronar}^ ligaments, and 

 from the outer side of the ulna, and is inserted into the external and ante- 

 rior surface of the radius. It turns the radius outwards, so as to supinate 

 the hand. 



Extensor ossis metacarpi pollicis, or abductor pollicis longus, arises from 

 the middle of the posterior part of the ulna and 230sterior surface of the 



773 



