FOREARM AND HAND 145 



bone. It contains two tendons, viz. the tendons of the abductor 

 pollicis longus and the extensor pollicis brevis. The second 

 compartment corresponds with the most lateral groove on the 

 dorsal aspect of the radius. It is broad and shallow, and it 

 holds the tendons of the extensor carpi radialis longus, and 

 extensor carpi radialis brevis. The third compartment is formed 

 over the narrow, deep, oblique intermediate groove on the 

 dorsum of the distal end of the radius, and through it the 

 tendon of the extensor pollicis longus passes. The fourth 

 compartment is placed over the wide shallow groove which 

 marks the medial part of the dorsal aspect of the distal end of 

 the radius. It is traversed by five tendons, viz. the four 

 tendons of the extensor digitorum communis and the tendon 

 of the extensor indicis proprius. The fifth compartment is 

 situated over the interval between the distal ends of the 

 radius and ulna. It contains the slender tendon of the 

 extensor digiti quinti proprius. The sixth and most medial 

 compartment, which corresponds with the groove on the dorsum 

 of the distal end of the ulna, encloses the tendon of the 

 extensor carpi ulnaris. 



Extensor Tendons of the Fingers. The four tendons of 

 the extensor digitorum communis, when they emerge from their 

 compartment under the dorsal carpal ligament diverge on the 

 dorsum of the hand to reach the four fingers. The tendon of 

 the ring finger will be seen to be connected by a tendinous 

 slip with the tendon on either side of it. This explains the 

 small degree of independent movement in a backward direction 

 which the ring finger possesses. The arrangement of the 

 tendons on the fingers is the same in each case. Upon the 

 dorsal aspect of the first phalanx the tendon expands so as 

 to cover it completely. Into the margins of this "dorsal 

 expansion " the delicate tendons of the lumbrical and inter- 

 osseous muscles are inserted. Near the first interphalangeal 

 joint the expansion becomes marked off into three portions 

 a central and two lateral. The central part, which is the 

 weakest, is inserted into the dorsal aspect of the base of the 

 second phalanx. The stronger lateral portions unite into one 

 piece beyond this, and gain an insertion into the base of 

 the ungual phalanx. 



The tendon of the extensor indicis proprius joins the expan- 

 sion of the extensor tendon on the dorsal aspect of the first 

 phalanx of the index finger. 



VOL. i 10 



