=Vessels and Nerves.=—The =arteries= form anastomoses around the larger joints, and give off branches to the extremities of the bones and to the joint capsule. The synovial membrane has a close-meshed network of capillaries; the latter form loops around the margins of the articular cartilages, but do not usually enter them. The =veins= form plexuses. The synovial membrane is also well supplied with lymphatics. Nerve-fibers are especially numerous in and around the synovial membrane and there are special nerve-endings, _e. g._, Pacinian bodies and the articular end-bulbs described by Krause. =Movements.=—The movements of a joint are determined chiefly by the form and extent of the joint surfaces and the arrangement of the ligaments. They are usually classified as follows: 1. =Gliding.=—This refers to the sliding of one practically plane surface on another, as in the joints between the articular processes of the cervical vertebræ. 2. =Angular Movements.=—In these cases there is movement around one or more axes. Motion which diminishes the angle included by the segments forming the joint is termed =flexion=, while that which tends to bring the segments into line with each other is called =extension=. With reference to the joints of the lower parts of the limbs, it seems advisable to employ the terms =dorsal= and volar or =plantar flexion=, since these joints can be “overextended.” Similarly, the terms =dorsal= and =ventral flexion= should be applied to the corresponding movements of the spinal column. The meaning of the term =lateral flexion= is evident. These movements are all rotations around axes which are approximately either transverse or vertical. Depression, elevation, and lateral movement of the lower jaw fall in this category. 3. =Circumduction.=—This designates movements in which the distal part of the limb describes a circle or a segment of one. In man such movement is easily performed, but in quadrupeds it is possible to a limited degree only, and is to be regarded usually as an indication of disease. 4. =Rotation.=—As a matter of convenience, this term is reserved to indicate rotation of one segment around the longitudinal axis of the other segment forming the joint. It is seen typically in the atlanto-axial joint. 5. =Adduction= and =abduction= designate respectively movement of a limb toward and away from the median plane, or of a digit toward and away from the axis of the limb. =Classification.=—This is based on the form of the joint surfaces and the movements which occur. The following chief classes may be recognized: 1. =Arthrodia=, or gliding joint. In these the surfaces are practically flat, admitting of gliding movement. Examples: carpo-metacarpal joints; joints between the articular processes of the cervical and thoracic vertebræ.