96 Articulation of Bones. [Book IX 



merous procefles of two bones, like the teeth of faws, 

 are mutually received into each other, as in the bones 

 of the head; and 2dly, by the growing together of 

 bones with the intervention of cartilage, as in the union 

 of the os facrum with the ofla innominata. 



The ends of bones which move on each other are 

 tipped with fmooth cartilage ; and the friction is flill 

 further diminifhed by a fluid, much more flippery than 

 oil itfelf, which is called the fynovia. The moveable 

 joints are alfo furnifhed with ftrong membranes, called 

 ligaments, which pafs from one bone to another, afford- 

 ing ftrength, and retaining the heads of the bones in 

 their cavities. For the purpofes of articulation, and 

 the connection of mufcles, bones are uneven on their 

 furface, and have numerous elevations and depref- 

 fions. 



