THE UPPER EXTREMITY. 105 



THE UPPER EXTREMITY. 

 THE SHOULDER. 



The shoulder is formed by the clavicle and the scap- 

 ula, and serves to connect the upper extremity with the 

 trunk. 



THE CLAVICLE 



is classed among the long bones, although it does not 

 possess a medullary cavity. It is shaped like the letter S, 

 and presents two curves, a sternal anterior convex and 

 a scapular anterior concave. It articulates with the 

 sternum and acromial process of the scapula, and forms 



nHtitl Ixt.9 



FIG. 48. THE LEFT CLAVICLE, UPPER SURFACE. 



the only osseous connection of the superior extremity 

 with the skeleton. 



It is placed horizontally; its articulations, arthrodial 

 in character, and with the extraordinary elasticity of the 

 bone, preserve the trunk from shock, the result of violence 

 to the shoulder or upper extremity. 



Owing to the peculiarities of its position and articu- 

 lation, it allows of great latitude of motion. It consists 

 of 39 per cent, organic and 61 per cent, inorganic matter. 

 It presents for examination two extremities and the shaft. 

 The outer extremity, including the outer one-third of the 

 shaft, is flattened from above downward, presenting an 

 upper and under surface, posterior and anterior borders, 

 which are marked for the insertion of the trapezius and 

 deltoid, respectively. The under surface presents the 



