152 ARTICULATION. 



being destitute of a synovial membrane, like the non- 

 articular. These are found in the interosseous spaces ; and 

 the sacro-sciatic ligaments belong to this class. Besides 

 ligament, there are other elements entering into the con- 

 stitution of joints, as bone, cartilage, fibro-cartilage, and 

 synovial membrane. Each of these will be noticed in its 

 proper place. 



The different forms of articulation are arranged in three 

 classes : 



1. Diarthrosis, 2. Synarthrosis, 3. Amphiarthrosis. 



Diarthrosis (&a, through, apfyoi', a joint,) is a movable 

 articulation, and constitutes the great number of the joints. 

 There are three varieties of this articulation, according to 

 the degree of motion enarthrosis, arthrodia, and ging- 

 lymus. 



Enarthrosis (sv, in, opflpov, a joint,) has the greatest range 

 of motion of all the joints; it is called the ball and socket- 

 joint, from the form of the bones, and the manner of their 

 connection, as the hip and shoulder. Arthrodia is an artic- 

 ulation having a more limited range of motion, as the 

 clavicle, ribs, articular processes of the vertebrae, radius and 

 ulna, carpus, tarsus, &c. Ginglymus (rtyy^oj, a hinge,) is a 

 hinge-like joint, where the motion is backwards and for- 

 wardS; flexion and extension, as seen at the elbow, knee, and 

 ankle. A variety of the hinge-joint, called the rotatory, is 

 fbund between the radius and ulna. The synarthrosis (ow, 

 together, apflpov, a joint,) is the articulation without motion, 

 where the bones are immovably connected together. There 

 are four varieties of this joint : 



1. TheSutura. 3. Schindylesis. 



2. Harmonia. 4. Gomphosis. 



The suture has several varieties; it is serrated when the 

 .bones come together and interlock, by processes at their 

 margins, resembling the teeth of a saw, as in the coronal, 

 .sagittal, and lambdoidal sutures of the cranium. It is called 

 -squamous (squama, a scale,) when the bones overlap, as 

 the temporal and parietal at the side of the head. Har- 

 monia, (op, to adapt,) is a species of suture, where the con- 



