228 STRUCTURE AND ADAPTATION OF TEETH 



Crustacea, as in the lobster, might claim our atten- 

 tion ; or the formidable apparatus of lancet and 

 saw-like teeth with which the Annelides, especially 

 the marine genera, are furnished. But, perhaps, 

 we should find still greater cause for admiration, 

 in the multitudinous lingual teeth of the Mollusca, 

 whether adapted for rasping vegetable food, as in 

 the periwinkle, or for drilling holes in the hardest 

 shells, as in the whelk and other carnivorous 

 molluscs. 



In this great division — the animals destitute of 

 either skull or vertebral column, — the arrange- 

 ment of the teeth is as strange as their forms. 

 The organs supplying the place of jaws are 

 arranged circularly, as in the sea-urchin ; vertically, 

 as in the insects ; triangularly, as in the leech ; or 

 forming a long flexible riband, as in the mollusc, 

 with many other variations to which we cannot 

 make even a passiag reference. But when we 

 turn to the higher or vartebrate division, we per- 

 ceive that the jaws of fishes, reptiles, and mammals, 

 and the bills of birds, are invariably arranged in 

 the horizontal plane, and never exceed two in 

 number. 



It was originally my intention to take a cursory 

 view of the teeth in the several orders of mammals, 

 passing in the ascending series, fi:*om the horny 

 teeth of that strange paradox, the ornithorhyn- 

 chus, with its duck-like mandibles and webbed 

 feet, to the more perfect teeth of the higher orders ; 



