120 ARTICULATIONS IN GENERAL. 



cartilages completely encloses the joint cavity. The bones are further held 

 together by fibrous tissue in the various forms of ligaments, such as mem- 

 branous capsules, flat bauds, or rounded cords. These ligaments, it is true, 

 are not so tight as to maintain the bones in close contact in all positions of 

 the joint, but are rather tightened in some positions arid relaxed in others, 

 so that they may be looked upon chiefly as controllers of the motions. The 

 bones are likewise held together in diarthrodial joints, by atmospheric 

 pressure, and by the surrounding muscles. 



MOTIONS OF THE BONES IN THE JOINTS. 



The various movements of the bones on one another in the joints are dis- 

 tinguished by different terms according to their directions, viz., angular 

 movement, circumduction, rotation, and shifting ; but it is proper to remark 

 that although different kinds of motion, answering to these several terms, 

 may readily be recognised, yet there are few of the motions which occur in 

 the joints which are of one sort only, but rather several kinds of movement 

 are frequently combined in one, and they also run into one another in great 

 variety. 



Angular movement, or opposition, is movement in such a manner as to 

 increase or diminish the angle between two bones, so that they shall lie more 

 or less nearly in a straight line. The different kinds of angular movement 

 are designated by different terms according to the directions in which they 

 take place with reference to the limb or body : thus, flexion and extension 

 indicate angular movements, which have the effect of bending or straightening 

 parts upon one another or upon the trunk of the body : adduction and abduc- 

 tion indicate angular movement to and from the mesial plane of the body, 

 or, when fingers and toes are referred to, these terms may be used to denote 

 movement to and from the middle line of the hand or foot. 



Circumduction is the movement performed when the shaft of a long bone 

 or a part of a limb describes a cone, the apex of which is placed in the joint 

 at or near one extremity of the bone, while the sides and base of the cone 

 are described by the rest of the moving part. 



Rotation signifies movement of a bone round its axis without any great 

 change of situation. 



Shifting is a term which may be applied to that kind of movement in 

 which the surfaces of adjacent bones are displaced without any accompanying 

 angular or rotatory motion, as in the sliding of flat surfaces over each 

 other, such as in some of the carpal and tarsal articulations, or in the move- 

 ment of advance and retreat of the lower jaw. 



The term ginglymus is used to distinguish a hinge joint, or one which admits only 

 of flexion and extension. Enarihrosis (Cruveilhier) is the ball-and-socket form of 

 joint, like the shoulder and hip, allowing motion in every direction. Artkrodia 

 is employed by Winslow and Cruveilhier to signify a joint admitting of very little 

 movement. 



In the preceding paragraphs attention has been called only to the directions of the 

 movements of the parts united in the joints, but the movements of opposed articular 

 surfaces relatively one to another are likewise worthy of notice. 



In the movements of the joints, when occurring between separate opposed 

 surfaces, there is generally more or less of a gliding motion of one surface on the 

 other ; but it is to be observed that in some joints a small amount of motion may be 

 produced without gliding, by the alternate contact and separation of different parts 

 of the opposed surfaces, to which the name of coaptation (Goodsir) has been applied ; 

 and that in other joints the articular surface of one bone may travel over that of 

 another, so as to bring different parts of the surfaces successively into contact, in the 



