978 



PISCES. 



teeth in both jaws would project forwards in- 

 stead of being opposed to one another, and 

 such, in fact, must have been their position 

 were it not that, as in Pimelepterus, the teeth 

 are bent at nearly a right angle with their 

 base. In the Scarus, and likewise in the mar- 

 ginal teeth of the Diadon, where these organs 

 are straight and attached horizontally to the 

 margin of the jaws, their sides instead of their 

 crowns are actually opposed to each other. 



In the Cod-fish, Wolf-fish, and some other 

 species, in proportion as the ossification of the 

 tooth advances towards its base and along 

 the connecting ligamentous substance, the 

 subjacent portion of the jaw-bone receives 



Fig. 512. 



Portion of the. jaw of Lophhis piscatorius, showing the 

 ligamenfous attachment of the teeth. 



a, a, a, anterior teeth; b, b, b, posterior teeth in their 

 erect position ; cyone of these teeth laid flat towards 

 the interior of the mouth, the dotted lines indicating 

 its condition when erect. (After Owen.) 



a stimulus and developes a process cor- 

 responding in size and form with the so- 

 lidified basis of the tooth. In this case the 

 inequalities of the opposed surfaces of the 

 tooth and maxillary dental process fit into each 

 other, and for some time they are firmly at- 

 tached together by a thin layer of ligamentous 

 substance ; but, in general, anchylosis takes 

 place to a greater or less extent before the tooth 

 is shed. The small anterior maxillary teeth of 

 the Angler ( Lophius ) are thus attached to the 

 jaw, but the large posterior ones remain always 

 moveably connected by highly elastic glisten- 

 ing ligaments, which pass from the inner side 

 of the base of the tooth to the jaw-bone 

 (fig. 512, f/). These ligaments do not permit 

 the tooth to be bent outwards beyond the ver- 

 tical position, when the hollow base of the 

 tooth rests upon a circular ridge growing from 

 the alveolar margin of the jaw; but the liga- 

 ments yield to pressure upon the tooth in the 

 contrary direction, and its point may thus be 

 directed towards the back of the mouth ; the 

 instant, however, that the pressure is remitted, 

 the tooth flies back, as by the action of a 

 spring, into its former position. The deglu- 

 tition of the prey of this voracious fish is thus 

 facilitated and its escape prevented. 



The teeth of the Wolf-fish, Anarrhicus, are 



extremely remarkable. They do not adhere 

 immediately to the jaw or to the palate bone, 

 but are attached to conical or hemispherical 

 osseous epiphyses, which are fixed to these bones 

 by a kind of suture, and are easily detached at 

 certain periods. The base of each of these 

 epiphyses is surrounded with a row of small 

 foramina, doubtless intended for the admission 

 of vessels, and mark the line of separation. 

 On the summit of these cones the true teeth, 

 formed as usual of dentine and enamel, are at- 

 tached, 



" If," says Professor Owen, in the valuable 

 treatise from which we have extracted the pre- 

 ceding paragraphs, " the engineer would study 

 the model of a dome of unusual strength and 

 so supported as to relieve from its pressure 

 the floor of a vaulted chamber beneath, let 

 him make a vertical section of one of the 

 pharyngeal teetli of the Wrasse (Jig. 513). 

 The base of this tooth is slightly contracted 

 and is implanted in a shallow circular cavity, 

 the rounded margin of which is adapted to a 

 circular groove in the contracted part of the 

 base. The margin of the tooth which thus 

 immediately transmits the pressure to the 

 bone is strengthened by an inwardly project- 

 ing convex ridge. The masonry of this inter- 

 nal buttress and of the dome itself is composed 

 of hollow columns, every one of which is 

 placed so as best to resist or to transmit in 

 a due direction the superincumbent pres- 

 sure." The use of this beautiful piece of 

 animal mechanics is to keep the delicate 

 successional pulp which is lodged beneath 

 the vault of the arched tooth, from being 

 injured by pressure during the action of these 

 powerful crushing teeth. 



Fig. 513. 





Teeth of the Wrasse ( Crenilabrus). 

 Portion of the pharyngeal bone of the Wrasse, 

 a, structure of arched teeth ; b, successional teeth ; 

 c, bone. 



la Rhizodus, a large extinct species of 

 Sauroid fish, the broad base of the tooth is 

 divided into a number of long and slender 

 cylindrical processes, which are implanted like 

 piles in the coarse osseous substance of the 

 jaw. They diverge as they descend, and their 

 extremities bend and subdivide like the roots 

 of a tree and are ultimately lost in the bony 

 tissue. This mode of attachment of a tooth is 

 perhaps the most complicated met with in the 

 animal kingdom. 



In order to complete our remarks concerning 

 the teeth of Fishes it only remains to notice a 

 few examples in which the dentition is peculiar, 

 namely, in the Cyprinidae, the Scari, the Dio- 

 dons, and the Tetradons. 



