. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 452 MOTION. those of the posterior; this tends to throw the centre of gravity a little in advance of the middle of the quadrilateral figure described by the four legs of the quadruped on the plane of position. Although the bones of the posterior extre- mities are inclined to each other at a greater obliquity than those of the anterior, they have the calcaneum projecting considerably beyond the axis of the calcaneo-tibial articulation, so that, acting with the advantage of a powerful le- ver, the wasteof muscular force is
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 452 MOTION. those of the posterior; this tends to throw the centre of gravity a little in advance of the middle of the quadrilateral figure described by the four legs of the quadruped on the plane of position. Although the bones of the posterior extre- mities are inclined to each other at a greater obliquity than those of the anterior, they have the calcaneum projecting considerably beyond the axis of the calcaneo-tibial articulation, so that, acting with the advantage of a powerful le- ver, the wasteof muscular force is diminished,and the disadvantage arising from their obliquity is partially compensated. The time and order in which the legs of quadrupeds succeed each other in motion determine the paces deno- minated the walk, the trot, the gallop, the amble, and the leap, or bound. In order to illustrate many of the general principles on which the progression of qua- drupeds is effected, we shall select the horse as an example. In standing, the animal rests its trunk on the legs which form the four columns of support. Let us suppose the legs to be placed on the ground at A B E D (fig. 245): if these points be joined, they form a rectangular parallelogram. When the animal walks slowly with his right side in advance, the left hind leg moves first; the right fore leg second ; the right hind leg third ; and the left fore leg fourth. During these four successive motions, the centre of gravity is propelled forwards over a space equal to the length of one step. Let us now investi- gate what takes place during these successive motions. The hind foot having been pre- viously extended, and having urged the centre of gravity forward, is first moved; it is then flexed, lifted from the ground, and advanced from E to e. Whilst the leg E is in the act of advancing to e, the trunk is supported on three legs, A B D, thus having the base of support transferred from the plane of a rec- tangular parallellogram
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