. The microscope and its revelations. \> MUSCLE 1049 the one hand from the connective tissue that binds the fibres intofasciculi, and equally distinct from the internal substance of thefibre. This membranous tube, which is termed the sarcoleinma, isnot perforated by capillary vessels, which therefore lie outside theultimate elements of the muscular substance ; whether it is pene-trated by the ultimatefibres of nerves is a pointnot yet certainly ascer-tained. The diameter ofthe fibres varies greatlyin different kinds of verte-brated animals. Its ave-rage is greater in reptilesand fishes than
. The microscope and its revelations. \> MUSCLE 1049 the one hand from the connective tissue that binds the fibres intofasciculi, and equally distinct from the internal substance of thefibre. This membranous tube, which is termed the sarcoleinma, isnot perforated by capillary vessels, which therefore lie outside theultimate elements of the muscular substance ; whether it is pene-trated by the ultimatefibres of nerves is a pointnot yet certainly ascer-tained. The diameter ofthe fibres varies greatlyin different kinds of verte-brated animals. Its ave-rage is greater in reptilesand fishes than in birdsand mammals, and its ex-. PIG. 785. Striated muscular fibre, separatinginto fibril !;!•. of an whilst ininch, and teasing the the with tremesalso are wider; thus its dimensions vary in the frog from y^-oth to j^^th of an inch, and in the skate from ^th to human subject the average is about ^^jtl: extremes about ^-^th and ^-^th. The substance of the fibre, when broken up byneedles, is found to consist of very minute fibrilla3. which, whenexamined under a magnifying power of from 250 to 400 diameters,are seen to present a slightly beaded form, and to show the samealternation of light and dark spaces as whenthe fibrilla? are united into fibres or intosmall bundles (fig. 785). The dark and lightspaces are usually of nearly equal length;each light space is divided by a transverseline, called Dobies line, while each darkspace is crossed by a lighter band, known as* Hensens stripe. It has been generallysupposed that these markings indicate dif-ferences in the <v///y<ox///o// of the fibre ; butProfessor J. B.
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