The microscope and its revelations . Fig. 302. Perpendicular section of tooth of Lamna, moderatelyenlarged, showing network of medullary canals. Fig. 303. Transverse section of portion of tooth of Prisiis, morehighly magnified, showing orifices of medullary eanals, vnth systemsof radiating and inosculating tubuli. suiTounded by a system of tubuli (Fig, 303), which radiate into the surrounding solid substance. These tubuli, however, YT 2 692 YERTEBEATED ANIMALS. Fi&. do not enter lacunae, nor is there any concentric annulararrangement around the medullary canals; but each systemof tubuli
The microscope and its revelations . Fig. 302. Perpendicular section of tooth of Lamna, moderatelyenlarged, showing network of medullary canals. Fig. 303. Transverse section of portion of tooth of Prisiis, morehighly magnified, showing orifices of medullary eanals, vnth systemsof radiating and inosculating tubuli. suiTounded by a system of tubuli (Fig, 303), which radiate into the surrounding solid substance. These tubuli, however, YT 2 692 YERTEBEATED ANIMALS. Fi&. do not enter lacunae, nor is there any concentric annulararrangement around the medullary canals; but each systemof tubuli is continued onwards through its own division of thetooth, the individual tubes sometimes giving-off lateral branches, whilstin other instancestheir trunks bi-furcate. This ar-rangement is pe-culiarly well dis-played, when sec-tions of teethconstructed uponthis type areviewed as opaqueobjects (Fig. 304).—In the teeth ofthe higher Verte-brata, however, weusually find thecentre excavatedinto a single ca-vity (Fig. 305),and the remaiuderdestitute of vascular canals; but there are intermediatecases (as in the teeth of the great fossil Sloths) in whichthe inner portion of the dentine is traversed by prolonga-tions of this cavity, conveying blood-vessels, which do notpass iato the exterior layers. The tubuli of the non-vascular dentine, which exists by itself in the teeth ofnearly all MammaHa, and which in the Elephant is knownas ivory, all radiate from the central ca
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Keywords: ., bookcentury1800, booksubjectmicroscopes, booksubjectmicroscopy
