. The principles and practice of dental surgery. una; g Canals. Dentine is harder than bone or cementum, but less dense thanenamel. It is, apparently, disposed in concentric layers, arrangedone Avithin the other, parallel to the surface ofthe tooth—the last internal layer forming theboundary of the pulp-cavity. But in additionto this peculiar structural arrangement, it is,according to the microscopic observations ofPurkinje, Retzius, and Miiller, composed ofminute tubes or hollow fibres, radiating fromthe pulp-cavity to the periphery of the tooth,giving off, in their course, numerous branches,
. The principles and practice of dental surgery. una; g Canals. Dentine is harder than bone or cementum, but less dense thanenamel. It is, apparently, disposed in concentric layers, arrangedone Avithin the other, parallel to the surface ofthe tooth—the last internal layer forming theboundary of the pulp-cavity. But in additionto this peculiar structural arrangement, it is,according to the microscopic observations ofPurkinje, Retzius, and Miiller, composed ofminute tubes or hollow fibres, radiating fromthe pulp-cavity to the periphery of the tooth,giving off, in their course, numerous branches,as seen in Fig. 19, sometimes terminating insmall cells or corpuscles; and an amorphous p,„ o,,. Transversesec-or structureless intertubular substance. The l!: LVu^e^roo;o^CLaudoctrine of the tubularity of dentine is also lers,si?owiDgTheirnuir- , • T 1 ,1 , , 1 p ous anastomoses. sustained by the subsequent researches oi Professor Owen, Mr. Tomes, Kolliker and several other micro- scopists; while on the other hand, Mr. Alexander Nasmyth,. 46 ORGANS OF MASTICATION. FiCx. 21. equally distinguished as an odontologist, has seemingly demon-strated, by a series of beautiful and highly interesting experi-ments, that the canaliculi or tubes of these authors, are solidfibres composed of a series of little masses, succeeding eachother in a linear direction, like so many beads collected on astring. See Fig. 21. This appearance, however, which is not always conspicuous inthe human dentine, but is more remarkable in that of monkeys,ought not to mislead the observer: for the tubular character ofthe so-called dentine fibres, whether simple or baccated, maybe demonstrated in their microscopic sections, which, when dry orproperly mounted in Canada Balsam, exhibit the canaliculi filledwith air as black lines; or when moistened with turpentine orthin balsam allow the fluid to be seen to penetrate int© the tubules,,expel the air, and render the whole section extremely tubes
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