MOVEMENTS OF JOINTS. Ill 



Examples. 



fSutura .... bones of the skull. 

 ., . ) Harmonia . . . superior maxillary bones. 

 Synarthrosis.. gchindylesis ^ ^ vomer with rostrum. 



(.Gomphosis . . . teeth with alveoli. 

 Amphi-arthrosis . Bodies of the vertebrae . Symphyses. 



C Arthrodia . . . carpal and tarsal bones. 

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



(_ Enarthrosis . . hip, shoulder. 



The motions permitted in joints may be referred to four heads, viz. 

 1. Gliding. 2. Angular movement. 3. Circumduction. 4. Rotation. 



1. Gliding is the simple movement of one articular surface upon 

 another, and exists to a greater or less extent in all the joints. In the 

 least movable joints as in the carpus and tarsus, this is the only mo- 

 tion which is permitted. 



2. Angular movement may be performed in four different directions, 

 either forwards and backwards, as in flexion and extension ; or inwards 

 and outwards, constituting adduction and abduction. Flexion and ex- 

 tension are illustrated in the ginglymoid joint, and exist in a large 

 proportion of the joints of the body. Adduction and abduction con- 

 joined with flexion and extension, are met with complete, only in the 

 most movable joints, as in the shoulder, the hip, and the thumb. In 

 the wrist and in the ankle adduction and abduction are only partial. 



3. Circumduction is most strikingly exhibited in the shoulder and 

 hip joints ; it consists in the slight degree of motion which takes place 

 in the head of a bone against its articular cavity, while the extremity 

 of the limb is made to describe a large circle upon a plane surface. It 

 is also seen, but in a less degree, in the carpo-metacarpal articulation 

 of the thumb, metacarpo-phalangeal articulations of the fingers and 

 toes, and in the elbow when that joint is flexed and the end of the 

 humerus fixed. 



4. Rotation is the movement of a bone upon its own axis, and is 

 illustrated in the hip and shoulder, or better in the rotation of the cup 

 of the radius, against the eminentia capitata of the humerus. Rota- 

 tion is also observed in the movements of the atlas upon the axis, 

 in which the odontoid process serves as a pivot around which the 

 atlas turns. 



The structures entering into the composition of a joint are bone, 

 cartilage, fibrous tissue, adipose tissue, and synovial membrane. Car- 

 tilage forms a thin coating to the articular extremities of bones, some- 

 times presenting a smooth surface which moves on a corresponding 

 smooth surface of the articulating bone ; sometimes forming a plate 

 smooth on both surfaces and interposed between the cartilaginous ends 

 of two bones, interarticular ; and sometimes acting as the connecting 

 medium between bones without any free surface, interosseous. Fibrous 

 tissue enters into the construction of joints under the form of ligament, 

 in one situation constituting bands of various breadth and thickness, 



