186 OSSEOUS SYSTEM. 



*#. v The ulna with the radius rotates only, the atlas 

 with the dentatus; in these, luxation is very difficult. 



Q. Where do you find the articulations with sliding 

 motion alone? 



<ft. They are very numerous; the vertebra? on each 

 other; the carpus and metacarpus; the tarsus and meta- 

 tarsus; the sternal end of the ribs. 



Q. What do you mean by the immoveable articulations? 



Ji. Those where surfaces of juxta-position are so 

 wedged in as to retain the part; as the malar bone con- 

 fined between several other bones of the face. There is 

 an order of indented articulations immoveable as by suture; 

 there is another with implanted surfaces, as the teeth. 



Q. What effect has age on the articulation by suture? 



./?. It obliterates the suture by bony union. 



Q. Why do not the teeth unite to their sockets by 

 age? 



#. Because there is an intervening mucous membrane 

 not disposed to ossify. The teeth constitute the only or- 

 der with implanted surfaces. 



Q. What preserves the union of the immoveable articu- 

 lations? 



.#. Cartilages and membranes. The cartilages are 

 most conspicuous in infancy. 



Q. How are the moveable articulations united? 



Jl. By ligaments and muscles; these bonds of union are 

 freer in youth than age. 



Q. How does the office of cartilage differ in the im- 

 moveable and moveable articulations ? 



Jl. It is a bond of union in the first, and facilitates mo- 

 tion in the second, 



