_Comparative Anatomy._--The anterior fasciculus of the external lateral ligament of the ankle is only found in Man, and is probably an adaptation to the erect position. In animals with a long foot, such as the Ungulates and the Kangaroo, the lateral ligaments of the ankle are in the form of an X, to give greater protection against lateral movement. In certain marsupials a fibro-cartilage is developed between the external malleolus and the astragalus, and its origin from the deeper fibres of the external lateral ligament of the ankle can be traced. These animals have a rotatory movement of the fibula on its long axis, in addition to the hinge movement of the ankle. For further details of joints see R. Fick, _Handbuch der Gelenke_ (Jena, 1904); H. Morris, _Anatomy of the Joints_ (London, 1879); Quain's, Gray's and Cunningham's _Text-books of Anatomy_; J. Bland Sutton, _Ligaments, their Nature and Morphology_ (London, 1902); F. G. Parsons, "Hunterian Lectures on the Joints of Mammals," _Journ. Anat. & Phys._, xxxiv. 41 and 301. (F. G. P.) DISEASES AND INJURIES OF JOINTS The affection of the joints of the human body by specific diseases is dealt with under various headings (RHEUMATISM, &c.); in the present article the more direct forms of ailment are discussed. In most joint-diseases the trouble starts either in the synovial lining or in the bone--rarely in the articular cartilage or ligaments. As a rule, the disease begins after an injury. There are three principal types of injury: (1) sprain or strain, in which the ligamentous and tendinous structures are stretched or lacerated; (2) contusion, in which the opposing bones are driven forcibly together; (3) dislocation, in which the articular surfaces are separated from one another.