i8g6. 



THE TEETH OF FISHES. 383 



The commonest method of attachment of teeth to the jaw in 

 bony fishes is by anchylosis. The calcified tooth-substance and the 

 bone are in actual continuity, so that it is often difficult to distinguish 

 the line of junction. The connection is effected by a cement-like 

 substance, which is called by Tomes ' bone of attachment,' because 

 it develops from the periosteum of the jaw rather than from the 

 dental capsule. It is very coarse in texture, and full of irregular 

 lacunae : it is absorbed when the tooth falls, and is developed afresh 

 for the next tooth that occupies the same position. Instances of 

 anchylosed teeth are found in the pike, eel, haddock, and mackerel. 



Implantation of teeth in sockets is somewhat rare among fishes, 

 but examples occur of lodgment of teeth in complete alveoli, and of 

 numerous approximations towards this condition. The tooth and 

 bone are in organic continuity by means of a periosteal layer common 

 to the tooth and the jaw; and this layer may remain uncalcified, so 

 that the teeth can be pulled out of their sockets, as in some 

 Characinoid fishes ; or ' bone of attachment ' may, except in young 

 teeth, anchylose the tooth to the wall of its socket, e.g., Sphyrana. 



Form. — The greatest diversity of form is observable in the teeth 

 of fishes; in fact, as Owen points out (3, p. 1), "the teeth of fishes 

 offer more various and striking modifications than do those of any 

 other class of animals." In the aberrant ocean shark, Rhinodon, the 

 teeth have the form of small, closely set, slender pillars, standing out 

 at right angles to the surface of the jaw ; but in most sharks the 

 teeth are far larger in proportion, and are more important as organs 

 of prehension. They may have the form of pointed spines, circular 

 in section as in Scyllium, or compressed parallel to the axis of the jaw, 

 as in Carckarias. The edges of such trenchant compressed teeth may 

 be smooth and keen, as in Lamm, or finely serrated as in Carckarias 

 (Fig. 4), Galeocerdo, and Hemipristis. An accessory cusp or denticle 

 may be present on either side of the base of the main spine, as in 

 Odontaspis (Fig. 5) ; in the three-pronged teeth of Chlamydoselache these 

 lateral cusps are nearly as long as the median spine, and in the extinct 

 Diplodus considerably longer. Among extinct sharks, teeth with 

 multiple denticles are not uncommon, as, for instance, in Cladodus 

 (Fig. 6) and Hybodus. The lower teeth of Notidanus (Fig. 3), two 

 species of which still survive, have several such denticles on the 

 posterior side of the main cusp. No hard and fast line, however, can 

 be drawn between serrations and accessory cusps, the difference being 

 one of size only. 



While, in the compressed teeth of recent sharks, the portion 

 embedded in the gum lies nearly in the same plane as the part 

 exposed, in mesozoic fishes, e.g., Hybodus, the base is bent inwards, 

 and forms an obtuse angle with the crown, and in sharks of palaeozoic 

 times, e.g., Cladodus, the teeth are characterised by a broad horizon- 

 tally-expanded base, set nearly at right angles to the crown (Woodward, 

 10). In the archaic shark, Chlamydoselache, of the Japan seas, the base 



