THE HUMAN SKELETON. 



87 







Scapula, a, superior angle ; d, the glenoid cavity, or socket for the 

 round head of the arm bone ; m, the aeromion process : w, the coracoid 

 process, which serve to protect the joint ; /, the base ; g, the costa, or 

 inferior border, and 7i, the superior border of the triangle ; Z, the spine ; 

 o, the semi-lunar notch, for the passage of an artery, vein, and nerve. 



45. As a general rule, in the joints, strength and security 

 are sacrificed, in some degree, to obtain great freedom and 

 latitude of motion. Accordingly, we find that the shoulder 

 joint, which allows of more extensive motion than any other* 

 is also more frequently dislocated. In the hinge joints, such 

 as the knee and ankle, such an accident is comparatively 

 rare. Where a bone is dislocated, a regularly educated sur- 

 geon should, if possible, always be employed to reduce it, as 

 there is great danger in trusting to a natural bone-setter, so 

 called, who is entirely ignorant of the anatomy of the parts. 



46. The os humeri, or arm bone, is of a cylindrical shape, 

 and forms at the elbow a perfect hinge-joint with the two 



