230 SURGICAL APPLIED ANATOMY. [Chap. xiv. 



found mainly at the sides and in front. The lower the 

 section proceeds down the limb, the less will the bones 

 be covered at the sides, and the more equally will the 

 soft parts be found distributed about the anterior 

 and posterior aspects of the limb. It will be noticed 

 that where one bone is the most substantial the other 

 is the most slender, as near the elbow and wrist ; and 

 that it is about the centre of the limb that the twp 

 are most nearly of equal strength. The proximity 

 pf the two bones, and especially of the ulna, to the 

 posterior aspect of the limb permits them to be easily 

 examined from that surface, while it is from the 

 same aspect that resections and other operations upon 

 the bones are most readily performed. It will be 

 understood, moreover, that in compound fractures, 

 flue to penetration of fragments, the wound is more 

 usually on the posterior aspect of the limb. 



The important movements of pronation and supi- 

 nation take place between these bones, and round an 

 axis corresponding to a line drawn through the head 

 of the radius, the lower end of #ie ulna, and the 

 metacarpal bone of the ring-finger. Pronation is 

 mainly checked by the lower and middle parts of the 

 interosseous membrane, the posterior radio-ulnar liga- 

 ment, the inner part of the posterior ligament of the 

 wrist, and the opposition of the bones. Supina- 

 tion is chiefly limited by the lowest fibres of 

 the interosseous membrane, the anterior radio-ulnar 

 ligament, and the internal lateral ligament of the 

 wrist. "The chief influence in checking supination 

 is not to be found in ligament at all, but in the con- 

 tact of the posterior edge of the sigmoid cavity of the 

 radius with the tendon of the extensor carpi ulnaris, 

 as it lies in the groove between the styloid process and 

 the round head of the ulna " (H. Morris). Of the two 

 movements, supination is the more powerful. This 

 is illustrated in many ways. Jn using a screw-driver 



