|Henry Gray (18251861). Anatomy of the Human Body. 1918.|
|the apex is in the articular cavity; this kind of motion is best seen in the shoulder and hip-joints.|
Rotation.Rotation is a form of movement in which a bone moves around a central axis without undergoing any displacement from this axis; the axis of rotation may lie in a separate bone, as in the case of the pivot formed by the odontoid process of the axis vertebræ around which the atlas turns; or a bone may rotate around its own longitudinal axis, as in the rotation of the humerus at the shoulder-joint; or the axis of rotation may not be quite parallel to the long axis of the bone, as in the movement of the radius on the ulna during pronation and supination of the hand, where it is represented by a line connecting the center of the head of the radius above with the center of the head of the ulna below.
Ligamentous Action of Muscles.The movements of the different joints of a limb are combined by means of the long muscles passing over more than one joint. These, when relaxed and stretched to their greatest extent, act as elastic ligaments in restraining certain movements of one joint, except when combined with corresponding movements of the otherthe latter movements being usually in the opposite direction. Thus the shortness of the hamstring muscles prevents complete flexion of the hip, unless the knee-joint is also flexed so as to bring their attachments nearer together. The uses of this arrangement are threefold: (1) It coördinates the kinds of movements which are the most habitual and necessary, and enables them to be performed with the least expenditure of power. (2) It enables the short muscles which pass over only one joint to act upon more than one. (3) It provides the joints with ligaments which, while they are of very great power in resisting movements to an extent incompatible with the mechanism of the joint, at the same time spontaneously yield when necessary.
| The articulations may be grouped into those of the trunk, and those of the upper and lower extremities.|
|5. Articulations of the Trunk. a. Articulations of the Vertebral Column|
| These may be divided into the following groups, viz.:|
| I. Of the Vertebral Column.
|| VI. Of the Cartilages of the Ribs with the
Sternum, and with Each Other.
| II. Of the Atlas with the Axis.
|III. Of the Vertebral Column with
|| VII. Of the Sternum.
|IV. Of the Mandible.
||VIII. Of the Vertebral Column with the Pelvis.
| V. Of the Ribs with the Vertebræ.
|| IX. Of the Pelvis.
Articulations of the Vertebral Column
The articulations of the vertebral column consist of (1) a series of amphiarthrodial joints between the vertebral bodies, and (2) a series of diathrodial joints between the vertebral arches.
| 1. Articulations of Vertebral Bodies (intercentral ligaments).The articulations between the bodies of the vertebræ are amphiarthrodial joints, and the individual vertebræ move only slightly on each other. When, however, this slight degree of movement between the pairs of bones takes place in all the joints of the vertebral column, the total range of movement is very considerable. The ligaments of these articulations are the following:|
|The Anterior Longitudinal.
||The Posterior Longitudinal.
|The Intervertebral Fibrocartilages.
The Anterior Longitudinal Ligament (ligamentum longitudinale anterius; anterior common ligament) (Figs. 301, 312).The anterior longitudinal ligament is a broad and strong band of fibers, which extends along the anterior surfaces of the bodies of the vertebræ, from the axis to the sacrum. It is broader below than above,