The carpo-metacarpal joints of the index, middle, and ring fingers permit of little movement, whereas that of the thumb possesses free movement, and that of the little finger a much less degree. The distal heads of the four inner metacarpal bones are bound together by the transverse metacarpal ligament. Flexion of the two distal phalanges, without flexing the first, is performed with the aid of the extensor tendon, which first fixes the proximal phalanx. In extensor paralysis, therefore, this movement is not possible. The power of flexion of the distal phalanx alone is not generally possessed, but sometimes from injury, where the extensor tendon has been ruptured from its attachment to the terminal phalanx, that phalanx becomes flexed and fixed, the condition being known as mallet finger. The middle finger, owing to its greater length, is most exposed to shocks received by the fingers, and is well adapted to resist these, as its metacarpal bone rests on the cs magnum, which again communicates with the semilunar, and so with the strongest portion of the radius. Fractures of the metacarpal bones are common, the first being most frequently and the third least often affected. Fracture at the base of the first metacarpal is called Bennett's fracture (' stave of the thumb '). Avulsion of one or more fingers may be caused by machinery tears or bites of certain animals. In such cases not only the fingers, but also the tendons, may be dragged out from the forearm. Where only a single tendon comes away, it is generally that of the flexor profundus, but all the tendons may be so torn. As the palmar, or glenoid, ligaments in front of the fingers are more firmly attached to the distal than the proximal bones, they are carried with the distal bones, when dislocated, backwards, and cause considerable difficulty when reduction is attempted. The palmar ligament consists of a plate of fibro-cartilage firmly attached to the base of the phalanx on its palmar aspect, and but loosely attached to the proximal bone. The two sesamoid bones of the thumb are developed in the metacarpo-phalangeal plate, and a single sesamoid bone is frequently developed in the metacarpo-phalangeal plate of the index finger on its radial side. In the case of the thumb the outer bone gives attachment to the abductor and outer head of the flexor brevis, while the inner gives attachment to the adductor and inner head of the flexor brevis.