The costovertebral joints, articulations of the ribs with the vertebral column, may be divided into two sets, one connecting the heads of the ribs with the bodies of the vertebræ, another uniting the necks and tubercles of the ribs with the transverse processes.
1. Articulations of the Heads of the Ribs (articulationes capitulorum; costocentral articulations) —These constitute a series of gliding or arthrodial joints, and are formed by the articulation of the heads of the typical ribs with the facets on the contiguous margins of the bodies of the thoracic vertebræ and with the intervertebral fibrocartilages between them; the first, tenth, eleventh, and twelfth ribs each articulate with a single vertebra. The ligaments of the joints are:
2. Costotransverse Articulations (articulationes costotransversariæ) —The articular portion of the tubercle of the rib forms with the articular surface on the adjacent transverse process an arthrodial joint.
In the eleventh and twelfth ribs this articulation is wanting.
The ligaments of the joint are:
Movements.—The heads of the ribs are so closely connected to the bodies of the vertebræ by the radiate and interarticular ligaments that only slight gliding movements of the articular surfaces on one another can take place. Similarly, the strong ligaments binding the necks and tubercles of the ribs to the transverse processes limit the movements of the costotransverse joints to slight gliding, the nature of which is determined by the shape and direction of the articular surfaces. In the upper six ribs the articular surfaces on the tubercles are oval in shape and convex from above downward; they fit into corresponding concavities on the anterior surfaces of the transverse processes, so that upward and downward movements of the tubercles are associated with rotation of the rib neck on its long axis. In the seventh, eighth, ninth, and tenth ribs the articular surfaces on the tubercles are flat, and are directed obliquely downward, medialward, and backward. The surfaces with which they articulate are placed on the upper margins of the transverse processes; when, therefore, the tubercles are drawn up they are at the same time carried backward and medialward. The two joints, costocentral and costotransverse, move simultaneously and in the same directions, the total effect being that the neck of the rib moves as if on a single joint, of which the costocentral and costotransverse articulations form the ends. In the upper six ribs the neck of the rib moves but slightly upward and downward; its chief movement is one of rotation around its own long axis, rotation backward being associated with depression, rotation forward with elevation. In the seventh, eighth, ninth, and tenth ribs the neck of the rib moves upward, backward, and medialward, or downward, forward, and lateralward; very slight rotation accompanies these movements.