TEETH OF FISHES. 



3G9 



2-17 



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 Chimserse 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- 

 es o 



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 (JMi/letes), four sides ( Scaras), 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 ' 

 {dentes villiformes, dents en velours 3 ); all the 

 teeth of the Perch are of this kind : when the 

 teeth are equally fine and numerous, but 

 longer, they are called ' ciliiform ' {dentes 

 eiliiformes) : when the teeth are similar to, but Tcetb of Myxme. xxi. 

 rather stronger than these, they are called ' setiform ' {dentes 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 ' (dentes raduli formes, dents en rape or en cardes, fig. 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 



Transverse section of tooth of Oryeleropus, 

 magn. v. 



l 



pi. 22. 



" v. pi. 28. 



VOL, 



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



B B 



