CHAPTER VI 

 ARTICULATIONS OR JOINTS 



The General Structure of Joints. The bones of 

 the human body are held in movable, immovable, or 

 mixed relations with each other, depending upon the 

 degree of action required in the various movements, 

 functions, and positions assumed by the body. The 

 parts entering into the formation of these relations 

 taking place between bones, comprise a joint or artic- 

 ulation they are: bones, ligaments, cartilage, and a 

 synovial membrane. 



Bones. The articular portions of bones are enlarged 

 to form a joint of suitable size, so that muscles passing 

 over the joint can act at a greater angle. The layer 

 of bone beneath the cartilage entering into a joint is 

 a compact articular lamella. 



Cartilage. There are three varieties of cartilage- 

 hyaline, fibrocartilage, and yellow elastic (see page 

 51 for description of cartilage). The fibrocartilage 

 and hyalin are utilized in the structure of a joint; 

 the former where slight movement and great strength 

 are required as between vertebrae and the pubic bones 

 of the pelvis; the latter where freedom of movement 

 is essential, and a greater surface for general con- 

 venience of mutual connection is demanded, as in the 

 shoulder- and hip-joints, etc. 



Ligaments. The ligaments connecting the immov- 

 able joints, such as the bones of the skull, consist of 

 a thin layer of fibrous membrane called sutural liga- 

 ments, and have a layer of cartilage interposed as 

 the bones of the base of the skull. 



