DENTAL SYSTE.M OF FISHES. Hi 



It is interesting to observe in this class the process arrested at 

 each of the well-marked stages through which the development of a 

 mammalian tooth passes. In all fishes the first step is the simi)le 

 production of a soft vascular papilla from the free surface of the 

 buccal membrane : in Sharks and Rays these papillas do not proceed 

 to sink into the substance of the gum, but are covered by caps of an 

 opposite fi'ee fold of the buccal membrane ; these caps do not contract 

 any organic connection with the papilliform matrix, but, as this is 

 converted into dental tissue, the tooth is gradually withdrawn from 

 the extraneous protecting cap, to take its place and assume the erect 

 position on the margin of the jaAv (v. pi. 5.^^. 1.) Here, therefore, 

 is represented the first and transitory 'papillary' stage of dental de- 

 velopment in mammals ; and the simple crescentic cartilaginous 

 maxillary plate, with the open groove behind containing the germinal 

 papillae of the teeth, oiFers in the Shark a magnified representation of 

 the earliest condition of the jaws and teeth in the human embryo. 



In many Fishes, e. g., Lophius, Esox, the dental papilla? become 

 buried in the membrane from which they rise, and the surface to 

 which their basis is attached becomes the bottom of a closed sac : 

 but this sac does not become inclosed in the substance of the jaw ; so 

 that teeth at different stages of growth are brought away with the 

 thick and soft gum, when it is stripped from the jaw-bone. The final 

 fixation of teeth, so formed, is effected by the development of liga- 

 mentous fibres in the submucous tissue between the jaw and the base 

 of the tooth, which fibres become the medium of connection between 

 those parts, either as elastic ligaments, or by continuous ossification. 

 Here, therefore, is represented the 'follicular' stage of the develop- 

 ment of a mammalian tooth; but the 'eruptive' stage takes place 

 without previous inclosure of the follicle and matrix in the substance 

 of the jaw-bone. 



In Balistes, Scams, Sphyrcena, the Sparoids, and many other 

 Fishes, the formation of the teeth presents all the usual stages which 

 have been observed to succeed each other in the dentition of tlie 

 higher vertebrata : the papilla sinks into a follicle, becomes sur- 

 rounded by a capsule, and is then included within a closed alveolus of 

 the growing jaw, where the development of the tooth takes place and 

 is followed by the usual eruptive stages. A distinct enamel-pulp is 

 developed from the inner surface of the capsule in Balistes, Scams, 

 Sargus, and Chrysophrys. 



In all" Fishes the teeth are shed and renewed, not once only, as in 

 IVIammals, but frequently, during the whole course of their lives. 

 The maxillai-y dental plates of Lepidosiren, and the rostral teeth of 

 Priotis (if these modified dermal spines may be so called) are, per- 



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