Elements of animal physiology, chiefly human . ber of very minute wavy tubes (thedental tuhuU), which anastomose with each other. (See fig. 31.) 140. The Crusta Petrosa—cementum or cortical sub-stance—is the layer or crust of true bone, which,surrounds or covers the hidden portion of the toothfrom the neck to the end oi the faiig. (See fig. 31.) 141. Muscular Fibre.—The peculiar property of mus-cular fibre is its contractility, or power of sliortening,under the influence of the will or of nervous stimulus,or under that of chemical, mechanical, or electrical irri-tation. There are two kinds of
Elements of animal physiology, chiefly human . ber of very minute wavy tubes (thedental tuhuU), which anastomose with each other. (See fig. 31.) 140. The Crusta Petrosa—cementum or cortical sub-stance—is the layer or crust of true bone, which,surrounds or covers the hidden portion of the toothfrom the neck to the end oi the faiig. (See fig. 31.) 141. Muscular Fibre.—The peculiar property of mus-cular fibre is its contractility, or power of sliortening,under the influence of the will or of nervous stimulus,or under that of chemical, mechanical, or electrical irri-tation. There are two kinds of muscular fibre—smoothand striated. (See Animal Mechanics.) 142. Non-Striated (Organic) Muscular Fibre, alsotermed smooth unstriped muscular fibre, forms the chiefconstituent of the involuntary and of the hollow muscles,as those of the alimentary canal, the bladder, the gall-bladder, the coats of the arteries and of the excretoryducts and larger lymphatics. It is also found in thetrachea, the iris, the skin, and elsewhere. Its contrac-. la natui-al state. Treated with Acetio Acid to show the Nucleus, Plain Muscular Fibro:^>i from the Bladdei. Fig. 32. Smooth (Involuntary) Muscular in the hair-sacs, from cold or fright, causes the hairto rise—thus making the hair stand on end; italso produces goose-skin. VOLUNTARY MUSCLE. Ultimate FibriUs, A Striated MuscularFibre. Organic muscular fibre consists of minute elongatedfusiform (spindle-sliaped), flattish, nucleated, contractile^hre-cells of a pale yellowish colour, about -j^Vs *^ srVoof an inch in diameter, and q^ to -gj^ of an inch inlength. By their union, they form minute ribbon-likefilaments or fibres, which do not contain any sheath orsarcolemma. The primi-tive nucleated cells ofwhich they are composedreadily separate whentreated with nitric acid. 143. A VoluntaryMuscle; that is, amuscle which acts accord-ing to, or is controlledby, the impulses of thewill—consists of a bundleof bundles of striatedmusc
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