DENTAL SYSTEM OF FISHES. 



22o 



The true teeth of all Vertebrates consist, like bone, of an animal 

 gelatinous basis, hardened by salts of lime, magnesia, and soda ; the 

 phosphates of lime predominating. Analyses of the teeth of the Pike, 

 Car}), and Shark, will be found in V. pp. Ixiv. and 9. ; and in Lxxxv. 



The tubes which convey the capillary vessels through the substance 

 of the osteo- and vaso-dentine of the teeth of fishes * were early re- 

 cognised, on account of their comparatively large size ; as by Andre 

 e. g., in the teeth of Acanthurus, and by Cuvier and Von Born in the 

 teeth of the Wolf-fish and other species, f Leeuwenhoek had, 

 also, detected the much finer tubes of the peripheral dentine of the 

 teeth of the Haddock. These ' dentinal tubuli ' are given off from 

 the parietes of the vascular canals, and bend, divide, and subdivide 

 rapidly in the hard basis-tissue of the interspaces of those canals in 

 osteo-dentine (V. pi. 7.) ; the dentinal tubuli alone are found in true 

 dentine, and they have a straighter and more parallel course, usually 

 at right angles to the outer surfiice of the dentine (V. pi. 7. and pi. 52. b). 



I give the name ' vaso-dentine ' to that modification of the tissue in 

 which the vascular canals run nearly parallel with, and equidistant 

 from, each other, through the major part of the extent of such modified 

 dentine ; it is exemplified in the rostral teeth of the Saw-fish, the 

 maxillary dental plates of the ChimcErce, Psammodonts, andMi/liobates: 

 in the latter each medullary canal and its system of dentinal tubes 

 represents a slender subcylindrical denticle, being separated from the 

 contiguous denticles by a thin coat of bone or ' cement.' The dense 

 covering of the jaws of the Scari consists of a stratum of quite distinct 

 prismatic denticles, standing vertically to the surface of the bone. 



' Osteo-dentine' is that tissue in which the medullary canals are 

 wavy, irregular, and anastomotic ; in Mammalia it contains the 

 Purkingian cells ; in fishes it usually is covered more or less thickly 

 by hard dentine. Those conical teeth which, when fully formed, 

 consist wholly or in great part of osteodentine or vasodentine, always 

 first appear with an apex of true dentine. In some fishes the 

 simple_^central basal pulp-cavity of such teeth, instead of breaking up 

 into ii'regular or parallel canals, sends out a series of vertical plates 

 from its periphery, which, when calcified, give a fluted character to 

 the base of the tooth ; (Lepidosteus oxyurus, lxxxvi. pi. v. fig. 1.) 

 Sometimes such radiating vertical basal plates of dentine are wavy 

 in their course, and send off narrow processes from their sides ; and, 

 as a thin layer of the outer capsule interdigitates Avith the outstanding 



* The vaso-dentine of Pristis and Myliohates is like tliat of the teeth of the Cape 

 Anteater ( Ori/ctcropus') : the vaso-dentine of the Psammodonts resembles that 

 which forms the base of the tooth of the Sloth and Megatherium : the vaso-dentine 

 of Mammals differs from the osteo-dentine in the absence of the radiated ' I'urkin- 

 gian' cells. 



f See V. ]). 10. 



VOL. IL Q 



