32 



STRUCTURE OF TORTOISES. 



Sea Tortoise, are remarkably beautiful, and are employed in the 

 arts under the name of Tortoise shell. 



13. The eyes of Tortoises are protected by three lids like those 

 of birds. The tympanum is large, but ordinarily concealed be- 

 neath the skin, and the nostrils are pierced through the extremity 

 of the muzzle. 



14. As we have already stated, these animals are unprovided 

 with teeth, and their jaws are furnished with a horny envelope, 

 with cutting edges, like those of birds. Some live on marine 

 plants, and others on small animals as well as vegetables. They 

 require little nourishment, and they have been known to pass 

 months, and even years without eating. 



15. The elevator muscles of the jaw are very powerful, and 

 when a Tortoise has seized hold of any thing in the mouth, it is 

 almost impossible to get it away. The tongue is more compli- 

 cated in its structure than that of most Reptiles : it is thick, and 

 studded with tiliform papilla?. The stomach does not seem to 

 differ from the neighbouring parts of the digestive tube, except 

 that it is rather larger ; the intestine is of moderate length, and 

 has no ccecum ; the liver is voluminous. 



16. The lungs are very large, and lodged in the same cavity 



with the other viscera,* (Fig. 7.) The 

 mechanism by which the air enters them 

 is entirely different from that of other 

 animals in which the thorax is dilatable. 

 The parietes of this cavity being im move- 

 able in most Tortoises, the air is forced 

 into these organs by the action of the 

 mouth. The jaws being closed, the animal 

 lowers the hyoid bone, which enlarges the 



Fig. 7. 



cavity of the mouth, and the air having 

 entered through the nostrils, the posterior 

 nares are closed, and then raising the hyoid 

 bone, as if to swallow, the air thus in- 

 closed, is forced to descend through the 

 trachea. Therefore, the animal breathes 

 by a sort of deglutition. 



* Explanation of the Figure. Viscera of a Tortoise m, the jaws, A, 

 the hyoid bone, o, the oesophagus, t, the trachea, />, p, the lungs, c, the 

 heart and principal vessels, /, the liver, i, the intestines, cl, the cloaca, 

 ov, the ovaries, ca, c, the carapax. 



13. Have Tortoises any eye-lids ? What is the character of the ear ? 

 Where are the nostrils situate ? 



14. Upon what do Tortoises feed ? 



15. What is peculiar in the tongue of Tortoises ? What is the character 

 of the stomach and intestines ? 



16. How do Tortoises breathe ? 



