. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. MOTION. 447 scuta (which take a variable number of fixed points in the surface of motion), and enable them to propel the body forwards and supply the place of so many legs. Their muscular sys- tem, though capable of exerting great power, acts at a mechanical disadvantage, and is quickly exhausted. Serpents move by diffe- rent methods, and upon different principles of progression. First, in a straight line, with the whole ventral aspect of the trunk in contact with the plane of motion. Secondly, in a curved line, with the
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. MOTION. 447 scuta (which take a variable number of fixed points in the surface of motion), and enable them to propel the body forwards and supply the place of so many legs. Their muscular sys- tem, though capable of exerting great power, acts at a mechanical disadvantage, and is quickly exhausted. Serpents move by diffe- rent methods, and upon different principles of progression. First, in a straight line, with the whole ventral aspect of the trunk in contact with the plane of motion. Secondly, in a curved line, with the trunk arched laterally, and the ventral aspect also in contact with the ground. Thirdly, in a curved line, with the body moving by an undulatory alternate elon- gation and contraction of small segments of the body. Fourthly, in a straight or curved line, with the trunk arched vertically in two or more curves. Fifthly, in a straight or curved line, with the trunk arched vertically in a single curve, consisting of the greater part of the trunk. Serpents possess also the power of climbing, swimming, and springing. In the first order of locomotion, or that of a straight line, with the whole of the ventral aspect resting immediately on the ground, the serpent is urged onwards by the oscillation of the ribs acting on the abdominal scuta, at successive points of its length. The scuta of a segment or seg- ments having secured a fulcrum in the plane of motion, the ribs connected with the fixed scuta, acting in turns, rotate backwards; the next segments in advance perform a similar action, until the whole series have completed the step. The length of the complete step depends on the arc through which the ribs oscillate, and the distances of the scuta from the axes of motion; and, as these are both small, and the motion has to be transmitted through the whole length of the reptile, this method of progression is, in consequence, very slow, presenting to the eye a tardy gliding movement.
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