SUPERFICIAL MUSCLES. 85 



ligament, to be inserted into the base of the metacarpal bone of insertion ; 

 the index finger. Along its outer border lies the radial nerve. 



Action. The long extensor straightens the wrist and abducts the and use. 

 hand ; it can also bend the elbow-joint. 



If the hand is fixed in climbing, it will act on the hunierus like 

 the long supinator. 



The EXTENSOR CARPI RADIALIS BREVIOR (c) is attached to the Extensor 



outer condyle of the humerus by a tendon common to it and the ^diaiis 

 three following muscles, viz., common extensor of the fingers, brevier: 

 extensor of the little finger, and ulnar extensor of the wrist ; it 

 takes origin also deeply from the external lateral ligament of the origin ; 

 elbow-joint. The tendon of the muscle is closely applied to the 

 preceding, and after passing with it through the same compartment 

 of the annular ligament, is inserted into the base of the metacarpal insertion ; 

 bone of the middle finger. 



Concealed on the outer side by the two preceding muscles, this parts 

 extensor rests on the radius and two of the muscles attached to it, ar 

 viz., supinator brevis, and pronator teres. Along its inner side is 

 the common extensor of the fingers ; and the extensors of the thumb 

 issue between the two. Each radial extensor has usually a bursa 

 l.eneath the tendon, close to its insertion. 



Action. This muscle acts in the same way as its fellow. and use. 



The EXTENSOR COMMUNIS DIGITORUM (D) is Single at its Origin, Common 



but is divided below into four tendons. It arises from the common 



tendon, from the fascia, and from aponeurotic septa between it and 



the adjacent muscles. At the lower part of the forearm the muscle origin; 



ends in four tendons, which pass through a compartment of the 



annular ligament with the extensor indicis, and are directed along division into 



the back of the hand to their insertion into the second and third Sndons; 



phalanges of the fingers. 



On the fingers the tendons have the following arrangement. On insertion 

 the dorsum of the first phalanx each forms an expansion with the 

 tendons of the lurnbricalis and interosseous muscles (fig. 29, p. 75). 

 At the lower part of that phalanx the expansion divides into three 

 parts (fig. 35, x) ; the central one is fixed into the base of the 

 second phalanx, while the lateral pieces unite, and are inserted into 

 the base of the last phalanx. Opposite the first two articulations of 

 each finger the tendon sends down lateral bands to join the capsule 

 of the joint. On the fore and little fingers the expansion is joined 

 by the special extensor tendons of those digits. 



This muscle is placed between the extensors of the wrist and relations of 

 little finger, and conceals the deep layer. On the back of the hand 

 the tendons are joined by cross bands (L), thinnest between the 

 index finger tendon and its neighbour, and strongest between the 

 ring finger tendon and its collateral tendons, so that they prevent 

 the ring finger being raised if the others are closed. 



Action. The muscle straightens the fingers and separates them use, 

 from each other. It acts especially on the first phalanges, the two ger^ 6 

 interphalangeal joints being extended mainly by the interosseotis 

 and lumbricales muscles. 



