OSTEOLOGY 45 



formed. The structures that enter into the formation of 

 a joint are bone, cartilage, fibrocartilage, ligament, and 

 sy no vial membrane. 



Bone constitutes the fundamental element of all the 

 joints. Cartilage is a firm, opaque, pearly-white, or bluish- 

 white in some varieties yellow highly elastic, flexible 

 tissue, possessed of considerable cohesive power. It 

 yields readily to pressure, and resumes its shape when the 

 force is removed. The synovial membrane will be con- 

 sidered when the membranes of the body are described. 



The movable joints of the human body are classified 

 according to their range of motion as follows : 



( i. Hinge joints. 

 Umaxial joints: \ _. . . L 

 ( 2. Pivot joints. 



f i. Condyloid joints. 

 Biaxial joints: < 



Saddle joints. 



[ i. Gliding joints. 

 Poly axial joints: -\ _ ., . . 



( 2. Ball-and-socket joints 



In the hinge joint the motion is about a transverse axis. 

 Examples the ankle-joint and part of the elbow- joint 

 (the articulation between the humerus and the ulna). In 

 the pivot joint the motion is about a longitudinal axis. 

 Examples the joint between the atlas and the axis and 

 part of the elbow- joint (the articulation between the 

 ulna and the head of the radius. 



In the condyloid joint the two axes of motion are placed 

 at right angles to one another, but both pass through the 

 same bone. Examples the wrist- joint and the articula- 

 tion between the atlas and the occiput. The saddle joint 

 is formed by the approximation of two saddle-shaped sur- 

 faces, the axes of motion being at right angles to each 

 other, but passing through different bones. Example 

 the carpometacarpal joint of the thumb. 



