50 ANATOMY FOR NURSES. [CHAP. V. 



and admit of only a limited amount of gliding movement, 

 as in the joints between the articular processes of the ver- 

 tebrae. 



(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. 



(4) Pivot joints. In this form, one bone rotates around 

 another which remains stationary, as in the articulation of the 

 atlas with the axis, and in the articulation of the ulna and 

 radius. In the articulation of the ulna and radius, the ulna 

 remains 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 forwards and 

 backwards. 1 When the palm is turned forwards, the attitude 

 is called supination ; when backwards, pronation. 



(5) Condyloid joints. When an oval-shaped head, or con- 

 dyle, 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 wrist. 



(6) Saddle joints. 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 

 " articulated " with the saddle by such a joint. For the saddle 

 is concave 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 backwards. The metacarpal bone of the thumb is 

 articulated with the wrist by a saddle joint. Both the con- 



1 Anatomists always speak of the body as being in the erect position, with 

 the arms hanging, and the palms of the hands looking forwards. 



