OSSEOUS SYSTEM. 183 



Articulations of the Osseous System. 



Q. How are the general classes of articulations divided? 



Jl. Into those with, and those without mobility. 



Q. To what purposes are the articulations with mobility 

 directed? 



Jl. They belong to the bones of locomotion. 



Q. Where are those without mobility found? 



*ft. In the bones whose union forms cavities to defend 

 the important organs. 



Q. What motions do the articulations with mobility 

 allow ? 



ft. There are four motions, viz. of opposition, circum- 

 duction, rotation and sliding. 



Q. What do you understand by the motion of opposi- 

 tion? 



#. It is simple flexion and extension abduction and 

 adduction. 



Q. What is the motion of circumduction? 



A. Circumduction is a movement in which the bone 

 describes a kind of cone, the apex of which is in the su- 

 perior articulation, and the base in the inferior. Circum- 

 duction comprises all the motions of opposition. 



Q. How does rotation differ from circumduction? 



#. In this, that in circumduction the bone has loco- 

 motion, in rotation there is none; in rotation the bone 

 turns on its own axis. 



Q. What is the sliding articulation? 



A. It is a motion appertaining to all the articulations, 

 and one described by the term. 



