TEETH OF FISHES. 377 



teeth of most of the Chretodonts are flexible, elastic, and composed 

 of a yellowish subtransparent albuminous tissue ; such, likewise, 

 are the labial teeth of the Helostome, the premaxillary and 

 mandibular teeth of the Goniodonts, and of the percoid genus 

 Tricliodon. In the Cyclostomes the teeth consist of a denser 

 albuminous substance. The upper pharyngeal molar of the Carp 

 consists of a peculiar brown and semitransparent tissue, hardened 

 by salts of lime and magnesia. The teeth of the Flying-fish 

 (Exocatus) and Sucking-fish (fiemora) consist of osteo-dentine. 

 In many Fishes, e. g. the Acanthurus, Sphyrcena, and certain 

 Sharks (Lamna, fig. 241), a base, or body of osteo-dentine, is 

 coated by a layer of true dentine, d, but of unusual hardness, like 

 enamel : in Prionodon this hard tissue predominates. In the 

 Labrus the pharyngeal crushing teeth consist wholly of hard or 

 imvascular dentine, fig. 240. In most Pycnodonts and Cestra- 

 cionts, and many other Fishes, the body of the tooth consists of 

 ordinary unvascular dentine, covered by a modification of gano- 

 dentine. In Sargus and BaUstes the body of the tooth consists 

 of true dentine, and the crown is covered by a thick layer of a 

 denser tissue, differing from the ' enamel ' of Mammalia only in 

 the more complicated and organised mode of deposition of the 

 earthy salts. The ossification of the capsule of the complex 

 matrix of these teeth covers the enamel with a thin coating of 

 ' cement.' In the pharyngeal teeth of the Scarus a fourth sub- 

 stance is added by the ossification of the base of the pulp after 

 its summit and periphery have been converted into hard dentine ; 

 and the teeth, fig. 262, thus composed of cement, c, enamel, e, 

 dentine, d, and osteo-dentine, are the most complex in regard to 

 their substance that have yet been discovered in the animal 

 kingdom. 



The tubes which convey the capillary vessels through the 

 substance of the osteo- and vaso-dentine of the teeth of Fishes 

 were early recognised, on account of their comparatively large 

 size ; as by Andre, e. g. in the teeth of Acanthurus, v and by 

 Cuvier and Von Born in the teeth of the wolf-fish and other 

 species. Lceuwenhoek had also detected the much finer tubes 

 of the peripheral dentine of the teeth of the haddock. 2 These 

 1 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 ; the 

 dentinal tubuli alone are found in true dentine, and they have a 



1 ccxlvii. 2 ccxlviii., p. 1003. 



