TEETH OF CETACEA. 127 



the Cetarea, where similar forms and arrange- 

 ments of teeth prevail. All the Dolphin tribe, such 

 as the Porpus, the Grampus, and the Dolphin, are 

 furnished with a uniform row of conical teeth, set 

 round both jaws, in number amounting frequently 

 to two hundred. Fig. 273, which represents the 

 jaws of the Porpus, shows the form of these simply 



prehensile teeth. The Cachalot has a similar row 

 of teeth, which are, however, confined to the lower 

 jaw. All these animals subsist upon fish, and their 

 teeth are therefore constructed very much on the 

 model of those of fish ; while those Cetacea, on the 

 other hand, which are herbivorous, as the Manalus 

 and the Dugorig, or Indian Walrus, have teeth very 

 differently formed. The tusks of animals must 

 necessarily, as respects their shape, be classed 

 among the conical teeth. 



The sharp-edged teeth perform the office of 

 cutting and dividing the yielding textures pre- 

 sented to them : they act individually as wedges or 

 chisels ; but when co-operating with similar teeth 

 in the opposite jaw, they have the power of cutting- 

 like shears or scissors. The flat teeth, of which the 

 surfaces are generally rough, are used, in conjunc- 

 tion with those meeting them in the oppsite jaw, 

 for grinding down the food by a lateral motion ; in 

 a manner analogous to tlie operation of mill-stones 



