ARTICULATIONS MOVEMENTS. 101 



tion of an elastic fibre-cartilage which adheres to the ends of both 

 bones. Examples of this articulation are seen in the union between 

 the bodies of the vertebra?, of the sacrum with the coccyx, of the 

 two first pieces of the sternum, the sacro-iliac and pubic sym- 

 physes (tfuv, ytswto grow together), and according to some, of the 

 necks of the ribs, with the transverse processes. 



DIARTHROSIS (Sia, through, agtogutfis) is the movable articulation, 

 which constitutes by far the greater number of the joints of the 

 body. The degree of motion in this class has given rise to a sub- 

 division into three genera, Arthrodia, Ginglymus, and Enarthrosis. 



Arthrodia is the movable joint in which the extent of motion is 

 slight and limited, as in the articulation of the clavicle, of the ribs, 

 articular processes of the vertebra?, axis with the atlas, radius with 

 the ulna, fibula with the tibia, carpal and metacarpal, tarsal and 

 metatarsal bones. 



Ginglymus (yiyyXu/j-oj, a hinge) or hinge-joint, is the movement of 

 bones upon each other in two directions only, viz. forwards and 

 backwards ; but the degree of motion may be very considerable. 

 The instances of this form of joint are numerous ; they comprehend 

 the elbow, wrist, metacarpo-phalangeal and phalangeal joints in the 

 upper extremity; and the knee, ankle, metatarso-phalangeal and 

 phalangeal joints in the lower extremity. The lower jaw may also 

 be admitted into this category, as partaking more of the character 

 of the hinge-joint than of the less movable arthrodia. 



The form of the ginglymoid joint is somewhat quadrilateral and 

 each of its four sides is provided with a ligament, which is named 

 from its position, anterior, posterior, internal or external lateral. 

 The lateral ligaments are thick and strong, and are the chief bond 

 of union between the bones. The anterior and posterior are thin 

 and loose in order to permit the required extent of movement. 



Enarthrosis (sv in, a^wrfis) is the most extensive in its range of 

 motion of all movable joints. From the manner of connexion and 

 form of the bones in this articulation, it is called the ball and socket 

 joint. There are three instances in the body, viz. the hip, the 

 shoulder, and the articulation of the metacarpal bone of the thumb 

 with the trapezium. 



The ball and socket joint has a circular form ; and, in place of 

 the four distinct ligaments of the ginglymus, is enclosed in a bag of 

 ligamentous membrane, called a capsular ligament. 



The kinds of articulation may probably be conveyed in a more 

 satisfactory manner in the tabular form, thus, 



Examples. 

 f Sutura .... bones of the skull. 



Synarthrosis J Har . monia . ' ' * su P erior maxillary bones. 



| Schindylesis . . vomer with rostrum. 



^Gomphosis . . . teeth with alveoli. 

 Amphi-arthrosis . Bodies of the vertebra? . Symphyses. 



C Arthrodia . . . carpal and tarsal bones. 



Diarthrosis. < Ginglymus . . . elbow, wrist, knee, ankle. 



( Enarthrosis . . hip, shoulder. 



