AND PHYSIOLOGY. 



67 



151. Symphyses. — Of Amphiarthrosis there is but one 

 VotcI, the Symphyses, or the apposition of two bones with 

 simply cartilage between. Examples of this are the arti- 

 culations of the vertebrae, and the ossa pubis. 



152. Arthrodia, Ginglymus, Enartlirosis. — Of Diarthro- 

 bis there are three vcriaties : Arthrodia, Ginglymus, and En- 

 artlirosis. Arthrodia is a slightly movable joint, as of the 

 wrist and ancle bones, or the radius and ulna. Ginglymu3 

 is the common hinge joint, where the degree of movement 

 is very considerable, but only in two directions. The best 

 example of this is in the knee. Enarthrosis is the ball * and 

 socket joint, that admits of movement in all directions. The 

 only cases of this articulation are in the shoulder, hip, and 

 tnumb. 



153. Anatomy of the Articulations. — In synarthrosis 

 there is simply a membrane interposed between the two bones 

 which keeps them in their places. In amphiarthrosis the 

 two extremities are partly covered with cartilage, lined by 

 synovial membrane, and partly connected by the interosseous 

 ligaments, or by an elastic fibro-cartilage which adheres to 

 both edges of the bones. In diarthrosis especially, as it is 

 exhibited in ginglymus, the general outline of the bone is 

 quadrilateral, upon each edge of which is found a ligament. 

 The lateral ones, however, are the main supports of the joint, 

 while the anterior and posterior ones are thin and a part of 

 the time loose, which are only of service to determine the 

 amount of movement in the joint. An example of this is 

 seen in the fingers, since they can only be extended so as 

 to lie in the axis of the metacarpal bones. The reason 

 why they can not be bent back upon the dorsal surface of 

 the hand is that the anterior ligament does not admit of suffi- 



151. Describe the Symphyses. Give an example. 152. Give the three varieties of Diar- 

 throsis. Give an example of Arthrodia, Ginglymus, and Enarthrosis. 153. What are 

 the component parts of the different articulations? Give the mode of articulation ol 

 the fingers. Why can not the finger be bent upon the back of the hand? 



