2. =Ginglymus=, or hinge-joint. In this class the joint surfaces consist usually of two condyles, or of a segment of a cylinder or cone, which are received by corresponding cavities. In typical cases the movements are flexion and extension, _i. e._, around a single transverse axis. Examples: occipito-atlantal and elbow joints. 3. =Trochoid=, or pivot joint. In these the movement is limited to rotation of one segment around the longitudinal axis of the other. Example: atlanto-axial joint. 4. =Enarthrosis=, or ball-and-socket joint. These are formed by a surface of approximately spherical curvature, received into a corresponding cavity. They are multiaxial, and allow of the greatest variety of movement, _e. g._, flexion, extension, rotation, abduction, adduction, circumduction. Examples: hip and shoulder joints.[29] AMPHIARTHROSES These joints, as the name indicates, share some characters with both of the preceding groups. In them the segments are directly united by a plate of fibro-cartilage, and usually by ligaments also. The amount and kind of movement are determined by the shape of the joint surfaces and the amount and pliability of the uniting medium.[30] These joints are all medial in position, and are best illustrated by the joints between the bodies of the vertebræ. There is usually no joint cavity, but in certain situations a rudimentary one exists. THE ARTICULATIONS OF THE HORSE JOINTS AND LIGAMENTS OF THE VERTEBRÆ The movable vertebræ form two sets of articulations, viz., those formed by the bodies, and those formed by the articular processes of adjacent vertebræ; the former are termed =intercentral=, and the latter, =interneural=. Associated with these are ligaments uniting the arches and processes; some of these are =special=, _i. e._, confined to a single joint, while others are =common=, _i. e._, extend along the entire vertebral column or a considerable part of it. The joints between the atlas and axis and between the former and the skull require separate consideration. INTERCENTRAL ARTICULATIONS These are =amphiarthroses=, formed by the junction of the extremities of the bodies of adjacent vertebræ. The =articular surfaces= in the cervical region consist of a cavity on the posterior end of the body of the anterior vertebra, and a corresponding convexity or head of the succeeding vertebra. In the other regions the surfaces are much flattened. The uniting media are: