LIGAMENTS. CARTILAGE. JOINTS 



37 



which glide over each other. In such cases the cartilaginous 

 surfaces are smooth, thus making the motion easier. The cartilage 

 which serves this purpose is called articular cartilage. 



Joints are distinguished as immovable and movable. 



Immovable joints are those in which the bones are in actual 

 contact, i.e. without any intervening cartilage ; and are incapable 

 of motion on each other. In some such joints, as in the skull, 



Fig. 41. The Joints of the Pelvis. 



i, ligament of the vertebrae ; ?, 3, 4, 5, 6, 7, and 8, other ligaments ; 9 and 10, ball and socket 

 joint of the hip in part dissected, to show the synovial cavity ; and also the ligament (liga- 

 mentum teres) which connects the ball of the lemur with the interior of the acetabulum. 



each bone has a very irregular sawlike edge, and the teeth or pro- 

 jections of the opposite edges are firmly dovetailed together. 

 Immovable joints are often called sutures (Lat. sutura, a seam). 



Movable joints are those in which the bones forming them 

 are capable of motion against each other. These joints are sub- 

 divided into perfect or complete, and imperfect or incomplete. 



The perfect joints are of four kinds, viz : (i) gliding joints, 

 consisting of bones which slide over each other, as those of the 

 ankle and wrist; (2) ball and socket joints, consisting of a 

 rounded head which rotates in a hollow socket, as the hip-joint and 

 shoulder-joint ; (3) hinge joints, like those of the elbow and the 



