Chap. XL] THE CLAVICLE. 171 



transverse, and may be at any part of the bone. 

 When about the middle third they present the 

 displacement just described. When the fracture is 

 between the conoid and trapezoid ligaments no dis- 

 placement is possible. When beyond these ligaments 

 the outer end of the outer fragment is carried forwards 

 by the pectorals and serratus, and its inner end is 

 a little drawn up by the trapezius. In this fracture 

 there is no general displacement downwards of the 

 outer fragment, since it cannot move in that direction 

 unless the scapula go with it, and the scapula remains 

 fixed by the coraco-clavicular ligaments to the inner 

 fragment of the clavicle. 



The clavicle may be broken by muscular violence 

 alone. Polaillon, from a careful analysis of the 

 reported cases, concludes that the muscles that break 

 the bone are the deltoid and clavicular part of the 

 great pectoral. In no case does the fracture appear 

 to have been produced by the sterno-mastoid muscle. 

 The commonest movements producing fracture appear 

 to be violent movements of the limb forwards and 

 inwards, or upwards. These fractures are usually 

 about the middle of the bone, and show no displacement 

 other than that of both fragments forwards, i.e., in the 

 direction of the fibres of the two muscles first named. 



The clavicle is more frequently the seat of 

 green -stick fracture than is any other bone in 

 the body. Indeed, one half of the cases of broken 

 collar bone occur before the age of five years. This 

 is explained by the fact that the bone is ossified 

 at a very early period, and is in a breakable condi- 

 tion at a time when most of the other long bones 

 still present much unossified cartilage in their parts. 

 Moreover, the periosteum of the clavicle is unduly 

 thick, and not very closely attached to the bone, cir- 

 cumstances that greatly favour subperiosteal fracture. 



A reference to the relations of the bone will 



