HOW ANIMALS EAT. 



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ture, and method of attachment. They are almost entirely used for 

 prehension, as nearly all fishes, like reptiles and birds, do not masticate 

 but gulp down their food as quickly as possible. The exceptions, how- 

 ever, are interesting. Some rays and the cestracion of Australia have 

 the jaws filled with teeth, flattened and joined together like blocks in 

 a pavement, or like mosaic. These are used to crush sea- weed and 

 mollusks. In a former geological age, this was the prevailing form 

 of teeth in the whole order of sharks. The common carp has its teeth 

 on the bones of the pharynx, and hence masticates its food in its 

 throat. For this purpose the food is sent back after being swallowed. 

 Some fishes are toothless, but most fishes have hundreds of teeth, fre- 

 quently covering all parts of the mouth. The teeth of fishes and of 

 reptiles are shed and replaced indefinitely. 



Fib. 7. Skui-ls and Teeth of Muskrat (Fiber zibetMcus). Size reduced. 1, cranium with 

 upper incisors overgrown, due to loss of lower incisors ; 2 a, skull and jaw with normal teeth ; 

 2 b y lower incisor removed, to show its great length. 



Reptilian teeth present no great variety. Toads, tortoises, turtles, 

 and some lizards are entirely destitute of teeth. Frogs have teeth in 

 the upper jaw. Those of serpents assist in swallowing the huge prey. 

 The poison-fangs of venomous species present a peculiar and complex 

 modification. They are fastened to movable bones which are worked 



