3G8 



ANATOMY OF VERTEBRATES. 



instances, as with certain dermal appendages, the reproduction of 

 the tooth is uninterrupted, or continuous. A tooth, when fully 

 formed, is subject to decay, but has no inherent power of 

 reparation. 



246 



Portion of transverse section of tooth of a Dendrodus, niagn. V. 



Thus teeth are analogous to epidermal and horny parts in their 

 mode of developement, in their shedding and reproduction, and 

 in their exposure to outward influences ; but the antlers of deer 

 are similarly exposed, and are likewise shed and renewed, yet, 

 like the teeth and horn-cores of the ox, they are classed with 

 the osseous tissues. 



§ 70. Teeth of Fishes. — In tins class of Vertebrates the teeth, 

 whether we study them in regard to their number, 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, fig. 125, 22, 32, the 

 Paddle- fish, and the whole order of Lopliohranchii, are edentulous. 

 The Myxinoids, fig. 248, have a single pointed tooth, a, on the 

 roof of the mouth, and two serrated dental plates, h, on the 

 tongue. The Tench has a single grinding-tooth on the occiput, 



