244 SURGICAL APPLIED ANATOMY. [Chap. xm. 



while in extension the hold of the coronoid process 

 upon that bone is even less. In a lateral direction, 

 however, movement has but a very slight effect upon the 

 support the bones mutually derive from one another. 



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

 luxated together than is either the radius alone or the 

 ul.na 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 displacement 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 iisually forwards, due to 

 the fact that the forms of violence that tend most 

 often to displace the bone tend also to draw it for- 

 wards. Paulet asserts that the posterior part of the an- 

 7iular 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 



