278 AMERICAN TESTUDINATA. Part II. 



SECTION X. 



EATING, DRINKING, AND DIGESTIVE APPARATUS. 



In describing the skin, we have already mentioned the characteristic horny 

 sheath of the jaws, which fomis a bill such as we find only in Birds besides. 

 The upper jaw always includes the lower, as it reaches beyond this. Generally, the 

 horny sheath which covers the jaws runs more or less inwards into the mouth; 

 in the Chelonioidae, it forms even several ridges parallel to the margin of the jaw, 

 evidently for crushing and breaking the thick sea-weeds, upon which they feed. 

 As all other Reptiles have true teeth and no horny cover whatsoever on the 

 maxillar bones, this sheath is peculiar to the order of Testudinata ; ^ and while aU 

 other Reptiles use their jaws merely for seizing their food. Turtles, on the contrary, 

 chew it. This is particularly the case with the herbivorous families, Chelonia and 

 Testudo. A much more extensive use of the tongue is connected with the act of 

 chewing, as long as the food is in the mouth, than we observe in other Reptiles. 

 Thus the ileshy tongue of the Turtles serves three different purposes: first, in 

 tasting, (see p. 277,) then in the act of respiration, (see p. 281,) and thirdly, in 

 managing the food as long as it is in the mouth; that is, for bringing it into 

 the right position between the sharp scissors formed by the bill, and for moving 

 it into the pharynx and oesophagus when it is sufficiently divided. The last two 

 uses of the tongue are the more interesting, as we do not meet them again, 

 to this extent, except in Mammalia. The tractus intestinalis has generally thick 

 walls. The oesophagus of the family of Chelonidoe is provided with long, hard 

 papilla\ The stomach lies always transversely, crossing the body from the left to 

 the right. The length of the whole intestine, in comparison with the length of the 

 trunk of the animal, varies very much in different families, being longer in the 

 herbivorous, and shorter in the carnivorous Turtles, just as among Mammalia and 

 Birds. The relative length of the different parts of the intestine, compared with 

 each other, varies still more ; the rectum being verj' short in EmydoidiB, Cinoster- 



^ Yet the order of Turtles is not tlie first among after removing the horny slieath, we find, along the 



Vertebrates, in which we find the jaws transformed dental ridges of the jaws, in the young Trionyx and 



into a bill. We find already something similar Chelydra, a regular series of holes for nerves, which 



among the Fishes, in the so-called Parrot Fishes, are evidently homologous to the alveolas of the teeth 



(Scarus,) and again among Amphibia, in the larvae in other Reptiles. These holes contain, however, no 



of the Batrachia anura. I may add, however, that rudimentary teeth, as are found in the jaws of Whales. 



