For the purpose of determining the characteristic shape of the articular surface of the fetlock, coronary and coffine joint of the horse, the author has computed analytical-geometrically the curves of the sawed articular surfaces of these joints. The following results were obtained. (1) The locus of the centers of curvature and fluctuation of the radius of curvature show that the sagittal curve on the joint is nearly a circle, but strictly speaking, these curves are supposed to be elipse or parabola and deviated from the circle. (2) Through the observation of the curvature of the sagittal sawed curve, the type of these joint-movements are the sliding partly containing the rolling. (3) The anatomical extents of the movement of these joints show about 28° at the coronary joint and 80° at the coffine joint, so the author recognized that the extent of the coffine joint-movement is far greater than that of the coronary joint. (4) By analysing the locus of a fixed point on the moving bone which are calculated from the approximate circles, the author asserts that the locus of the movement is epi- or hypocycloid.
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