COMPARATIVE ANATOMY OF THE TEETH. 293 



The osseous teeth, fixed in alveoli, are, after their full 

 development, described as being "closely soldered to the 

 circumference of the cavity in which they are placed." 



Those fish whose teeth are sharp, with a strong incli- 

 nation backwards as in the pike, or tooth-like and cutting 

 as in the shark, are regarded as the most carnivorous and 

 voracious. Those on the other hand whose teeth are flat- 

 tened, or only pharyngeal, are viewed as the least carnivor- 

 ous and most peaceable in their dispositions. 



SECOND DIVISION OP THE ANIMAL KINGDOM. 



THE INVERTEBRATA OR ANIMALS DESTITUTE OF A SPINE. 

 The teeth of this division have an analogy of function 

 with those of the vertebrata, being situated, many of 

 them, at or near the mouth of the alimentary tube, and 

 laying hold of, retaining, and dividing the food thus 

 performing the functions of prehension and mastication, 

 though in structure they are considered by some as farther 

 removed from true teeth than the hair. 



The teeth of the invertebrated division are mostly found 

 in the stomach a very singular and striking fact; and Mr. 

 Blandin remarks, " The higher the animal is elevated in 

 the scale, the higher are the dental organs elevated in the 

 alimentary canal. 



"In the Crustacea andmollusca they are placed principally 

 in the stomach. In fishes they reach the pharynx. In rep- 

 tiles the posterior part of the mouth whilst in the mam- 

 malia they are confined to the anterior and lateral parts of 

 the mouth." 



In the Crustacea the dental organs found in the stomach 

 consist of calcareous matter placed on a kind of skeleton. 

 This so-called skeleton of the stomach is composed of 

 transverse and lateral ribs, to which these teeth are at- 

 tached. Upon the lateral ridges the two larger teeth are 

 placed and have flat crowns, with depressions. The crown 

 in the crab is striated, and has on its inferior border large 

 " denticulations." 



The great lobster is described as having nine of the rib- 



