DENTAL SYSTEM OF FISHES. 219 



a branch of the anterior division of the fifth nerve enters each fol- 

 licle, makes a coil there, and quits it to join another filament, or to 

 i-eturn to its own stem.* 



LECTURE IX. 



DIGESTIVE SYSTEM OF FISHES. 



Dentition. 



The teeth of fishes, whether we study them in regard to their num- 

 ber, form, substance, structure, situation, or mode of attachment, offer 

 a greater and more striking series of varieties than do those of any 

 other class of animals. 



As to number, they range from zero to countless quantities. The 

 Lancelet, the Ammocete, the Sturgeon, the Paddle-fish {Jig. 61. o. b.), 

 and the whole order of Lophobranchii, are edentulous. The Myxinoids 

 have a single pointed tooth on the roof of the mouth, and two serrated 

 dental plates on the tongue. The Carp has a single grinding tooth 

 on the occiput, opposed to two dentigerous pharyngeal jaws below. 

 In the Lepidosiren a single maxillary dental plate is opposed to a 

 single mandibular one, and there are two small denticles on the nasal 

 bone. In the extinct Sharks with crusliing teeth, called Ceratodus 

 and Ctenodus, the jaws were armed with four teeth, two above and 

 two below. In the Chimcerge two mandibular teeth are opposed to 

 four maxillary teeth. From this low point the number in different 

 fishes is progressively multiplied until, in the Pike, the Silurus, and 

 many other fishes, tlie mouth becomes crowded with innumerable 

 teeth. 



With respect to form, I may first observe, that as organised beings 

 withdraw themselves more and more, in their ascent in the scale of 

 life, from the influence of common physical agents, so tlieir parts pro- 

 gressively deviate from geometrical figures : it is only, therefore, in 

 tlie lowest vertebi'ated class that we find teeth in the form of perfect 

 cubes, and of prisms or plates with three {Myletes), four {Scants), 



* Lxxvi. p. 332. pi. ill. figs. 10. 12. 



