CHAPTER XII. 

 THE UPPER EXTREMITIES. 



The upper extremities include the shoulders, arms, 

 forearms, wrists, and hands and contain each thirty- 

 two bones. The bones of the two shoulders taken to- 

 gether are called the shoulder girdle and consist of the 

 two clavicles or collar bones and the two scapulae or shoul- 

 der blades, which together make an almost complete 

 girdle of the shoulders. 



The clavicle is a long slender bone extending almost 

 horizontally from the sternum to the scapula and can 

 be felt for its whole length in the living. For the inner 

 two-thirds it is convex anteriorly, for the outer third 

 concave. In woman it is generally less curved, smoother, 

 and more slender than in man, and as bone is rough 

 when the muscles attached are powerful, the right clav- 

 icle, being used more, is generally rougher and thicker 

 than the left. Among the muscles attached are the 

 large neck muscle, the sterno-cleido-mastoid, whose 

 tendons form the presternal notch, the trapezius, the 

 pectoralis major, and the deltoid. 



Being slender and superficial the clavicle is most 

 frequently broken of any bone in the body, generally 

 by indirect violence, as by falling with the hand out, 

 though old people in such a case are apt to get Colles' 

 fracture at the wrist. The bone generally gives way 

 at the juncture of the outer and middle thirds, with 

 displacement of the parts inward, so that the fracture 

 is seldom compound. Since, however, the main ves- 

 sels of the upper arm, with their nerves, lie beneath the 

 clavicle, there is danger of their being punctured. Such 

 serious injury is guarded against by the presence of 



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