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For other uses, see Leg (disambiguation). In general, a leg is any of the parts of an animal's body that support the rest of the body above the ground, and are used for locomotion. Legs mostly come in even-numbered quantities that are characteristic of some taxonomic groups: * in vertebrates, 2 (the bipeds) or 4 (the quadrupeds); * in many familiar arthropods, 6, 8, or 12; * in some arthropods, more than a dozen and sometimes over 100 -- but despite what their names might suggest, ** centipedes seldom have exactly a hundred, and ** millipedes apparently never even approach a thousand. The human leg of course shares all the properties that are common to all non-human animals, and in particular, shares the more extensive properties that are common to all other mammals. Conversely, (nearly all) humans are legged animals and thus have several kinds of specialized resources available for studying and understanding non-human legs: * an accumulation of experience with the functioning (and occasional malfunctioning) of one type of animal leg; * the immediate opportunity to physically inspect a leg, and in fact to conduct experiments that have as results the collecting of some of the information transmitted in the leg's neurological system; * information about the anatomy and dynamics of the human leg that is socially transmitted for purposes related to health or to practical exploitation of one's own legs. [[zh:]]
It arises from the lateral condyle and upper half or two-thirds of the lateral surface of the body of the tibia; from the adjoining part of the interosseous membrane; from the deep surface of the fascia; and from the intermuscular septum between it and the Extensor digitorum longus.
It ends in a long tendon, which runs behind the lateral malleolus, in a groove common to it and the tendon of the Peronæus brevis, behind which it lies; the groove is converted into a canal by the superior peroneal retinaculum, and the tendons in it are contained in a common mucous sheath.
This is especially the case in standing upon one leg, when the tendency of the superincumbent weight is to throw the leg medialward; the Peronæus longus overcomes this tendency by drawing on the lateral side of the leg.
Clearly, the long lower leg sections, the leverage afforded by the powerful tendons, the low degree of weight in the legs, and the huge muscles located in the upper legs and torso all contribute to the speed and power of the horse.
Because the upper leg sections are relatively short, the major muscle groups (and weight) are all located close in to the body, improving the angular acceleration of the legs for speed, while the elongation of the lower leg segments greatly increases the stride.
All legs, be they front or back, have a joint which bends like a knee [rear knee, front pastern, human wrist] and another which bends like an elbow [rear hock, rear ankle, front elbow]; the net effect is the legs more or less "scissor" up and down in multiple segments.
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