86 ANATOMY FOR NURSES [Chap. VI 



admit of only a limited amount of gliding movement, as in the 

 joints between the articular processes of the vertebra?. 



(2) Hinge joint. — The articular surfaces are of such shape as 

 to permit of movement to and fro in one plane only, like a door 

 on its hinges. These movements are called flexion and extension, 

 and may be seen in the articulation of the arm with the forearm, 

 in the ankle joint, and in the articulations of the phalanges. 



(3) Ball and socket joint. — In this form of joint a more or 

 less rounded head is received into a cup-like cavity, as the head 

 of the femur into the acetabulum, and the head of the humerus 

 into the glenoid cavity of the scapula. Movement can take 

 place freely in any direction, but the shallower the cup, the 

 greater the extent of motion. The shoulder joint is the most 

 freely movable joint in the body. 



(4) Pivot joint. — In this form, one bone rotates around another 

 which remains stationary, as in the articulation of the atlas with 

 the axis (epistropheus) and in the articulation of the ulna and 

 radius. In the articulation of the ulna and radius the ulna re- 

 mains stationary, and the radius rotates freely around its upper 

 end. The hand is attached to the lower end of the radius, and 

 the radius, in rotating, carries the hand with it ; thus, the palm 

 of the hand is alternately turned forward and backward. When 

 the palm is turned forward, or upward, the attitude is called 

 supination ; when backward, or downward, pronation. 



(5) Condyloid joint. — When an oval-shaped head, or condyle, 

 of a bone is received into an elliptical cavity, it is said to form 

 a condyloid joint. An example of this kind of joint is found in 

 the metacarp()-])halangeal articulations. The rounded heads of 

 the metacarjial bones are rcrcjved in the elliptical-shaped bases 

 of the phalanges. 



(6) Saddle joint. — In this joint the articular surface of each 

 bone is concave in one direction, and convex in another, at right 

 angles to the former. A man seated in a saddle is " articu- 

 lated " with the saddle by such a joint. For the saddle is con- 

 cave from before backwards, and convex from side to side, while 

 the man presents to it the concavity of his legs astride, from 

 side to side, and the convexity of his seat, from before back- 

 wards. The metacarpal bone of the thumb is articulated with 

 the trapezius of the carpus by a saddle joint. Both the condy- 



