LECTURE VI 

 ARTICULATIONS OR JOINTS 



Articulations are divided into several groups for the pur- 

 pose of study. These groups are: immovable, slightly movable, 

 and freely movable. 



Examples: Immovable, between the skull bones; slightly mov- 

 able, between vertebras; freely movable, between scapula and 

 humerus. 



Freely movable articulations. — The freely movable articula- 

 tions are subdivided according to shapes of the articular sur- 

 faces and varieties of movement that can be produced. These 

 subdivisions are: ball-and-socket, hinge, pivot, imperfect hinge, 

 and gliding. 



The ball-and-socket articulation, of which we find examples 

 at the shoulder and hip, is made by a rounded head of one bone 

 fitted into a rounded cavity of some other bone ; for instance, at 

 the shoulder we have a rounded head of the humerus fitted into 

 the glenoid cavity of the scapula. At the hip a rounded head on 

 the superior extremity of the femur fits perfectly into the coty- 

 loid cavity of the pelvic bone. It will be readily seen that the 

 ball-and-socket joint permits the greatest variety of movements. 



The hinge joint is made by two articular surfaces of such 

 shape and so fitted together that no lateral or rotary motion is 

 possible. Only two movements are allowed at joints of this 

 kind: flexion and extension. The articulation between the 

 humerus above and the ulna and radius below offers a good 

 example of this kind. 



Pivot joint is one where portions of two bones are in contact 

 in such a way as to permit of rotary motion; for example, be- 

 tween the atlas and axis, the rotation being around the odon- 

 toid or toothlike processes of the axis. Articulations of this 

 kind permit of rotation only. 



The imperfect hinge joint is one which permits of two prin- 

 cipal motions — flexion and extension, and to a limited extent 

 some other motion, as for instance rotary or lateral movement. 



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