24 



THE FRAMEWORK OF THE BODY 



and frequently is, quite as serious as the breaking of a bone. 

 (Read Note 6.) 



9. The ligament, then, secures firmness to the joint ; it must 

 also have flexibility and smoothness of motion. This is ac- 

 complished by a beautiful mechanism, the perfection of which 



FIG. 7. THE LIGAMENTS OF THE WRIST 



FIG. 8. -CELLS OF CARTILAGE 



is only feebly imitated by the most ingenious contrivance of 

 man. The ends of the bones are covered by a thin layer of 

 cartilage, which, being smooth and elastic, renders all the 



6. How Joints may be Injured. "All the joints are liable to disloca- 

 tion that is, being 'put out' of their place. Owing to the shallowness 

 of the cavity at the shoulder, this joint is frequently dislocated ; and this 

 sometimes happens with the thigh, but not so often, as the cup in which 

 the femur moves is much deeper. Joints which have been dislocated 

 should at once be ' set ; ' but now that you have seen how liable you are 

 to accident, I hope you will be careful not to indulge in too violent or 

 rough exercise, by which you might not only dislocate the joints, and so 

 in time weaken them, but might also break the bones, and perhaps become 

 crippled for life. Many children have the habit of pulling their fingers 

 so as to make them ' crack.' This is exceedingly wrong, for it is to a 

 certain extent pulling the joints out of their sockets, and this may so 

 loosen the parts as to cause permanent injury." Davidson's " Our 

 Bodies." 



9. Office of the ligament? What must it have? 

 Svnovia? 



How accomplished ? Describe it. 



