. Animal physiology. Physiology, Comparative; Physiology, Comparative. 478 ATTITUDES OP ANIMALS. Of the Attitudes of the Body, and the various kinds of Locomotion. 650. A small number of Vertebrated animals,—Serpents, for instance,—bear habitually on the whole length of their bodies, which rest entirely on the ground; and their only movements are effected by undulations of the spinal column. But the rest are supported upon their extremities ; and we give the name of standing to that position, in which the animal rests supported by its limbs, upon the ground or any firm horizontal basis. In mai
. Animal physiology. Physiology, Comparative; Physiology, Comparative. 478 ATTITUDES OP ANIMALS. Of the Attitudes of the Body, and the various kinds of Locomotion. 650. A small number of Vertebrated animals,—Serpents, for instance,—bear habitually on the whole length of their bodies, which rest entirely on the ground; and their only movements are effected by undulations of the spinal column. But the rest are supported upon their extremities ; and we give the name of standing to that position, in which the animal rests supported by its limbs, upon the ground or any firm horizontal basis. In main- taining this position, the extensor muscles, by which the joints are straightened, must be in continual action, since the limbs would otherwise bend beneath the weight of the body. Now as the sense of fatigue, in a set of muscles, depends in great degree upon the length of time during which they have been in action, the maintenance of the standing posture for a long period is, in most animals, more fatiguing than walking; since in the latter exercise, the action of the flexors alternates with that of the extensors. 651. But this condition is not the only one essential to stea- diness in the standing posture ; for in order that the body may rest firmly upon the members, it must be in equilibrium. It has been shown (Mechan. Philos. Chap, iv.) that equilibrium ex- ists,—or in other words, that a body remains at rest in its position, —not only when it bears upon the whole of a broad surface, but also when it is so placed, that the tendencies of its different parts to descend or gravitate towards the earth, counterbalance each other. This is the case when its centre of gravity is supported,— that is, when a line drawn perpendicularly from it falls within the base. In order, then, that an animal may rest in equilibrium on its legs, it is necessary that the vertical line from its centre of gravity (or line of direction) should fall within the space which its feet cover an
Size: 2114px × 1182px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorcarpenterwilliambenja, bookcentury1800, bookdecade1840
