OF THE VERTEBRAL COLUMN. 265 



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THE KINDS OF MOVEMENT ADMITTED IN JOINTS. 



The movements admissible in joints may be divided into four kinds, gliding, 

 angular movement, circumduction, and rotation. 



Gliding movement is the most simple kind of motion that can take place in 

 a joint, one surface gliding over another. It is common to all movable joints; 

 but in some, as in the articulations of the carpus and tarsus, it is the only 

 motion permitted. This movement is not confined to plane surfaces, but may 

 exist between any two contiguous surfaces, of whatever form, limited by the 

 ligaments which inclose the articulation. 



Angular movement occurs only between the long bones, and may take place 

 in four directions, forwards and backwards, constituting flexion and extension, 

 or inwards and outwards, constituting adduction and abduction. The strictly 

 ginglymoid or hinge-joints admit of flexion and extension only. Abduction 

 and adduction, combined with flexion and extension, are met with in the more 

 movable joints ; as in the hip, shoulder, and metacarpal joint of the thumb, 

 and partially in the wrist and ankle. 



Circumduction is that limited degree of motion which takes place between 

 the head of a bone and its articular cavity, whilst the extremity and sides of 

 the limb are made to circumscribe a conical space, the base of which corres- 

 ponds with the inferior extremity of the limb, the apex with the articular 

 cavity; this kind of motion is best seen in the shoulder and hip-joints. 



Eotation is the movement of a bone upon its own axis, the bone retaining 

 the same relative situation with respect to the adjacent parts ; as in the articu- 

 lation between the atlas and axis, where the odontoid process serves as a pivot 

 around which the atlas turns ; or in the rotation of the radius upon the hurne- 

 rus, and also in the hip and shoulder. 



The articulations may be arranged into those of the trunk, those of the upper 

 extremity, and those of the lower extremity. 



ARTICULATIONS OF THE TRUNK. 



These may be divided into the following groups, viz : 

 I. Of the vertebral column. VII. Of the cartilages of the ribs with 



II. Of the atlas with the axis. the sternum, and with each 



III. Of the atlas with the occipital other. 



bone. VIII. Of the sternum. 



IV. Of the axis with the occipital bone. IX. Of the vertebral column with the 

 V. Of the lower jaw. pelvis. 



VI. Of the ribs with the vertebras. X. Of the pelvis. 



I. ARTICULATIONS OF THE VERTEBRAL COLUMN. 



The different segments of the spine are connected together by ligaments, 

 which admit of the same arrangement as the vertebras. They may be divided 

 into five sets. 1. Those connecting the bodies of the vertebras. 2. Those con- 

 necting the laminse. 3. Those connecting the articular processes, 4. Those 

 connecting the spinous processes. 5. Those of the transverse processes. 



The articulations of the bodies of the vertebras with each other form a series 

 of amphiarthrodial joints : those between the articular processes form a series of 

 arthrodial joints. 



