SYNARTHROS1S 265 



The ginglymus, or hinge-joint, is that form of joint in which the articular surfaces 

 are moulded to each other in such a manner as to permit motion only in one plane, 

 forward and backward; the extent of motion at the same time being considerable. 

 The direction which the distal bone takes in this motion is never in the same 

 plane as that of the axis of the proximal bone, and there is always a certain amount 

 of alteration from the straight line during flexion. The articular surfaces are 

 connected together by strong lateral ligaments, which form their chief bond of 

 union. The most perfect forms of ginglymus are the interphalangeal joints, 

 and the joint between the humerus and the ulna; the knee and ankle-joints are 

 less perfect, as they allow a slight degree of rotation or lateral movement in certain 

 positions of the limb. 



A trochoid, or pivot-joint or rotary joint, is one in which the movement is 

 limited to rotation; the joint is formed by a pivot-like process turning within 

 a ring, or the ring on the pivot, the ring being formed partly of bone, partly of 

 ligament. In the superior radioulnar articulation the ring is formed partly by 

 the lesser sigmoid cavity of the ulna and in the rest of its extent by the orbicular 

 ligament; here the head of the radius rotates within the ring. In the articulation 

 of the odontoid process of the axis with the atlas the ring is formed in front by 

 the anterior arch of the atlas; behind, by the transverse ligament; here the ring 

 rotates around the odontoid process. 



Condyloid or biaxial articulation is that form of joint in which an ovoid artic- 

 ular head, or condyle, is received into an elliptical cavity in such a manner as 

 to permit of flexion and extension, adduction and abduction and circumduction, 

 but no axial rotation. The articular surfaces are connected together by anterior, 

 posterior, and lateral ligaments. An example of this form of joint is found in 

 the wrist. 



Articulation by reciprocal reception, or saddle-joint, is that variety in which the 

 articular surfaces are concavo-convex; that is to say, they are inversely convex 

 in one direction and concave in the other. The movements are the same as in 

 the preceding form; that is to say, there is flexion, extension, adduction, abduction, 

 and circumduction, but no axial rotation. The articular surfaces are connected 

 by a capsular ligament. The best example of this form of joint is the carpo- 

 metacarpal joint of the thumb. 



An enarthrosis, or ball-and-socket joint, is that form of joint in which the distal 

 bone is capable of motion around an indefinite number of axes which have one 

 common centre. It is formed by the reception of a globular head into a deep 

 cup-like cavity, the parts being kept in apposition by a capsular ligament strength- 

 ened by accessory ligamentous bands. Examples of this form of articulation are 

 found in the hip- and shoulder-joints. 



Arthrodia. Arthrodia is that form of joint which admits of a gliding move- 

 ment ; it is formed by the approximation of plane surfaces or of one slightly con- 

 cave to one slightly convex, the amount of motion between them being limited 

 by the ligaments, or osseous processes, surrounding the articulation; as in the 

 articular processes of the vertebrse, the carpal joints, except that of the os magnum 

 with the scaphoid and semilunar bones, and the tarsal joints with the exception 

 af the joint between the astragalus and the scaphoid. 



Below, in tabular form, are the names, distinctive characters, and examples 

 of the different kinds of articulations. 



