The microscope and its revelations . n with the centralcavity, and are filled, like it, with marrow: in the shafts oflong bones, these canals usually run in the direction of theirlength, but are connected here and there by cross branches;whilst in the fiat bones, they form an irregular network.—Onapplying a higher magnifying power to a thin transverse sec-tion of a long bone, we observe that each of the canals whoseorifices present themselves in the field of view (Eig. 299), isthe centre of a rod of bony tissue (i), usually more or lesscircular in its form, which is arranged around it in conce
The microscope and its revelations . n with the centralcavity, and are filled, like it, with marrow: in the shafts oflong bones, these canals usually run in the direction of theirlength, but are connected here and there by cross branches;whilst in the fiat bones, they form an irregular network.—Onapplying a higher magnifying power to a thin transverse sec-tion of a long bone, we observe that each of the canals whoseorifices present themselves in the field of view (Eig. 299), isthe centre of a rod of bony tissue (i), usually more or lesscircular in its form, which is arranged around it in concentricrings, resembhng those of an Exogenous Stem. These ringsare marked-out and divided by circles of little dark spots ;which, when closely examined (2), are seen to be minuteflattened cavities excavated in the solid substance of thebone, from the two flattened sides of which pass-forth a VERTEBRATED ANIMALS. number of extremely minute tubules, one set extendinginwards, or in the direction of the centre of the system of Fig. Minute structure of Sone, as seen in transverse section:—1, anossicle surrounding an Haversian canal, 3, showing the concentricarrangement of the lamellae; 2, the same, with the lacuna andcanalicuh; 4, portions of the lamellae parallel with the externalsurface. rings, and the other outwards, or in the direction of itscircumference; and by the inosculation of the tubules (whichare termed canalictdi) of the different rings with each other,a continuous communication is estabhshed between thecentral Haversian canal and the outermost part of the bonyrod that surrounds it, which doubtless ministers to the nutri-tion of the texture. Bloodvessels are traceable into theHaversian canals; but the canaliculi, being far too minuteto carry blood-corpuscles, can only convey a nutrient fluid that is separatedFig. 300. from the blood for the special serviceof the bone. 404. The minutecavities, or lacuna(sometimes, but er-roneously termedbone-corpuscles, asif they
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