218 



APPLIED ANATOMY. 



hence they can raise the arm well out from the body and even higher than the 

 shoulder. In the rodents, as the squirrel, they are enabled to hold a nut firmly in 

 the paws while eating it. When, as in some of the lower orders, the function of 

 abduction is all important, we find not only the clavicles present and, as in the 

 common fowl, joined, forming the "wish-bone," but in addition, in birds, there is a 

 precoracoid bone formed by the coracoid process, which is enlarged and continued 

 forward to articulate with the sternum; thus in flying animals there are practically 

 two clavicles on each side. 



Affections of the Shoulder. The point of the shoulder projects well out 

 from the side of the thorax. Hence it is frequently injured. As the force is resisted 



Scapula 



Sternum 



FIG. 229. Shoulder-girdle in birds. Skeleton of an eagle, from the Wistar Institute: the clavicle, precoracoid, 

 and scapula form the shoulder-girdle; the two clavicles have fused in the median line, forming what is commonly 

 called the " wish-bone." 



by the bones, these receive the principal injuries and they are often broken. Frac- 

 tures of the clavicle dispute with those of the radius the distinction of being the 

 most numerous. Contusions produce more or less complete paralysis of the muscles, 

 not infrequently through lesions of the nerves. The laxity of the joint favors the 

 dislocations to which it is so frequently subject. It likewise becomes the seat of 

 tuberculous disease requiring resection. Crushes of the arm sometimes require its 

 removal at the shoulder-joint, and occasionally as the result of injury or disease opera- 

 tions may be required on the axillary lymph-nodes, nerves, or blood-vessels. 



In order to determine the character and extent of injuries to the shoulder, its 

 surface anatomy must be thoroughly known. In order to treat them, a knowledge 

 of the deeper structures and their relation to one another is essential. 



