220 SURGICAL APPLIED ANATOMY. [Chap. xm. 



slight effect upon the support the bones mutually 

 derive from one another. 



(b) Both bones of the fore-arm are more often 

 luxated together than is either the radius alone or the 

 ulna alone. This depends upon the powerful liga- 

 mentous connection between the radius and ulna on 

 the one hand, and the absence of such connection 

 between the humerus and the radius on the other. 

 In the dead subject it is not difficult to dislocate the 

 two bones of the fore-arm, but it is extremely difficult 

 to separate the radius from the ulna without great 

 breaking and tearing of parts. 



(c) The commonest dislocation of the two bones 

 together is backwards, the rarest is forwards. In 

 the former instance the movement is resisted by 

 the small coronoid process, in the latter by the 

 large and curved olecranon. For like reasons the 

 luxation outwards is less rare than is the displace- 

 ment inwards, since the articular surface of the 

 humerus inclines downwards and inwards on the 

 inner side, and thus affords a greater obstacle in 

 that quarter. 



(d) If a single bone be dislocated it will usually be 

 the radius. This follows from the absence of reliable 

 union between that bone and the humerus, from the 

 greater exposure of the radius ("the handle of the 

 hand") to indirect violence, and from its greater 

 mobility. The luxation is usually forwards, due 

 to the fact that the forms of violence that tend 

 most often to displace the bone tend also to draw 

 it forwards. Paulet asserts that the posterior part 

 of the annular ligament is " much more resistant " 

 than is the anterior part. The luxation of the ulna 

 alone occurs in the backward direction, for reasons 

 that will be obvious. 



Dislocations of the elbow of all kinds may be 

 partial or complete. More usually they are complete 



