TEETH. 125 



egress of prey. Mr. C. S. Tomes has shown that the means 

 by wliich this mechanism is worked are different in different 

 fishes ; for whilst, in the Pediculati and Gadoids (Hake) the 

 elasticity resides solely in tlie tissue of the hinge (the tooth 

 being as resilient as ever after everything else is severed), in 

 the Pike the hinge is not in the least endowed with elasticity, 

 but the bundles of fibres proceeding from the interior of the 

 dentine cap are exceedingly elastic. 



As regards texture the teeth of fishes show considerable 

 variation. The conical teeth of the Cyclostomes and the 

 setiform teeth of many Teleosteans consist of a horny albumi- 

 nous substance. The principal substance of the teeth of other 

 fishes consists of dentine, with numerous dividing and anasto- 

 mosing tubercles, sometimes covered by a stratum of unvas- 

 cular dentine. An enamel-like substance has been observed 

 on the crown of the teeth of Sargus and Balistes, and an ossi- 

 fication of the capsule of their matrix covers the enamel with 

 a thin coating of cement. The teeth either possess a cavity 

 in which the matrix is received, or, more frequently, they are 

 solid, in which case vascular canals of the underlying bone 

 are continued into the substance of the tooth. In the teeth 

 of some fishes numerous sets of canals and tubes are so 

 arranged that they do not anastomose with one another, each 

 set being surrounded by a layer of dentine and cement. 

 These apparently simple teeth are evidently composed of 

 numerous small teeth, and called compound teeth. 



The teeth may be, and generally are, very different as 

 regards size or form in the different parts of the mouth ; they 

 may be also different according to the age or sex of the fish 

 (Raja). The teeth may be few in number and isolated, or 

 placed in a single, double, or triple series, distant from one 

 another or closely set ; they may form narrow or broad hands, 

 or patches of various forms. As regards form, they may be 

 cylindrical or conical, pointed, straight, or curved, with or 



