TEETH OF FISHES. 



3G9 



247 



d- 



fig. 250, c, opposed to two dentigerous pharyngeal jaws, d, d, 

 below. In the Lepidosiren a single maxillary dental plate, 

 fig. 251, a, is opposed to a single mandibular one, b, and there are 

 two small denticles on the nasal bone, c. In the extinct Sharks 

 with crushing teeth, called Ceratodus and Ctenodus, the jaws were 

 armed with four teeth, two above and 

 two below. 1 In the Chimaerae two 

 mandibular teeth are opposed to four 

 maxillary teeth. 2 From this low point 

 the number in different Fishes is pro- 

 gressively multiplied until, in the 

 Pike, the Siluroids, fig. 252, and many 

 other fishes, the mouth becomes 

 crowded with innumerable teeth. 



With respect to form, I may pre- 

 mise that as organised beings with- 

 draw themselves more and more, in 

 their ascent in the scale of life, from 

 the influence of common physical 

 agents, so their parts progressively 

 deviate from geometrical figures : it 

 is. only, therefore, in the lowest ver- 

 tebrated class that we find teeth in the 

 form of perfect cubes, and of prisms 

 or plates with three sides (Myletes), four sides ( Scarus), five, or six 

 sides (Myliobates, fig. 249). The cone is the most common form in 

 Fishes : such teeth may be slender, sharp- 

 pointed, and so minute, numerous, and closely 

 aggregated, as to resemble the plush or pile 

 of velvet ; these are called ' villiform teeth ' 

 (denies villiformes, dents en velours*^); all the 

 teeth of the Perch are of this kind : when the 

 teeth are equally fine and numerous, but 

 longer, they are called ( ciliiform ' (denies 

 ciliiformes) : when the teeth are similar to, but 

 rather stronger than these, they are called ( setiform ' (denies seti- 

 formes, dents en brosse) : conical teeth, as close set and sharp 

 pointed as the villiform teeth, but of larger size, are called ' rasp- 

 teeth ' (denies raduliformes, dents en rape or en cardes, fio\ 252) ; 

 the Pike presents such teeth on the back part of the vomer : the 

 teeth of the Sheat-fish (Silurus glanis) present all the gradations 



1 v. pi. 22. 2 v. pi. 28. 



3 The French terms are those used by Cuvier in xxni. passim. 



VOL. I. BE 



Transverse section of tooth of 

 nmgn. v. 



248 



Teeth of Myxine. xxx. 



