Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . In that of the elephant, which is aboutan inch and a half in diameter, these radiatingfibres are very conspicuous, even to the nakedeye : and they are also visible in the membraneof the human ear, when viewed with a goodmicros(^ope.* At other times, the muscular fibres run in a * Home Phil. Trans, for 1800, p. 1. , tm THE MECHANICAL FUNCTIONS. circular direction, forming what is called anorbicular, or sphincter muscle, of which an exampleoccurs in that which surrounds and closes theeye. (Fi
Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . In that of the elephant, which is aboutan inch and a half in diameter, these radiatingfibres are very conspicuous, even to the nakedeye : and they are also visible in the membraneof the human ear, when viewed with a goodmicros(^ope.* At other times, the muscular fibres run in a * Home Phil. Trans, for 1800, p. 1. , tm THE MECHANICAL FUNCTIONS. circular direction, forming what is called anorbicular, or sphincter muscle, of which an exampleoccurs in that which surrounds and closes theeye. (Fig. 46.) Very frequently these two lastmodes of arrangement are united in some part,as appears to be the case in the membrane ofthe eye, called the Iris. (Fig. 47.) The circularfibres of the iris surround the central aperture,or pupil, the size of which they diminish whenthey contract; while on the contrary, the radi-ating fibres, acting on the inner circle, anddrawing it nearer to the outer circumference,which is fixed, lessen the breadth of the ring,and consequently enlarge the circular A similar combination of radiating and cir-cular fibres is employed in the construction offlat, or slightly concave muscular disks, whichare thus rendered capable of exerting a strongforce of adhesion to the surfaces on which theyare applied. In these organs the circular fibresare placed at the circumference, and the radi-ating fibres in the interior of the sucker, (seeFig. 48); so that, while the margin of the diskis closely applied to the object, the force result- MUSCULAR POWER. 137 ing from the contraction of the circular fibresis exerted to remove the central portions fromthe surface of attachment, and thereby tendsto create a vacuum underneath the disk ; thetwo surfaces remain, therefore, strongly attachedby the atmospheric pressure, which acts on theirouter sides. An apparatus of this kind, as weshall afterwards find, is met with very frequentlyamong the lower orders of the an
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