336 REPTILES. CHELOKIA. 



ORDER I. CHELONIA. 



Heart with two auricles; body enveloped in two plates or shields, 

 formed of the ribs and sternum ; four feet. 



In the Chelonian reptiles (so named from ^t\d>t),, a tortoise,) the heart consists of 

 two auricles, and a ventricle with two unequal chambers which communicate together. 

 ' The blood of the body enters the right auricle, that of the lungs into the left, but 

 both kinds of blood are partially mixed in passing through the ventricle. These 

 animals are distinguished externally by the double shield in which all their body 

 is inclosed, except their head, neck, tail, and feet. The upper shield or plate is 

 formed by their ribs, consisting of eight pairs, widened and united together, and at the 

 annular portion of the dorsal vertebrae by dentated sutures, in such a manner that all 

 these parts are deprived of mobility. The lower shield, or breast-plate, is formed of 

 pieces which are a substitute for the sternum, and which are generally to the num- 

 ber of nine. A circle of bony pieces, which appear analogous to the cartilaginous 

 part of the ribs in the mammalia, generally surrounds the upper shell, uniting all 

 the ribs which comprise it. The vertebrae of the neck and tail are alone moveable. 



These two bony cases being covered by the skin or by scales, the scapula, and 

 all the muscles of the arm and neck, in place of being attached to the ribs and spine, 

 are below, wlflch has made the tortoise be termed in this respect a retroverted ani- 

 mal. The vertebral extremity of the scapula is articulated with the shield, and the 

 opposite extremity of the clavicle with the breast- plate, in such a manner that the 

 shoulders form a ring for the passage of the trachea and oesophagus. A third bone, 

 larger than the other two, and directed backwards and downwards, represents, as in 

 birds, the coracoid apophysis. 



The lungs are extensive, and in the same cavity with the other viscera. The 

 thorax being immoveable in the greater number, it is by the action of the mouth 

 that the tortoise respires. Keeping the jaw shut, it alternately lowers and raises the 

 hyoid bone. The first movement allows the air to enter by the nostrils, and the 

 tongue afterwards closing the interior opening, the second movement forces the air 

 to penetrate into the lungs. 



Tortoises have no teeth ; their jaws are covered with horn, as the mandibles of birds, 

 except in the Chelides, where they are simply covered with skin. Their chest and 

 palatine arch are fixed to the cranium, and immoveable. Their tongue is short, and 

 rough with fleshy threads ; their stomach simple and strong ; and their intestines 

 of medium length, and deprived of coscum. 



Tortoises lay numerous eggs, covered with a hard shell. These eggs, deposited 

 in the warm sand, under a southern sun, and in summer, are hatched without the 

 parents' care by the influence of the atmosphere. The under shell or breast- plate of 

 the male is concave, that of the female cenvex. 



Tortoises are very tenacious of life, and they have been known to move without 

 the head for many weeks. They subsist on little food, and they are able to pass 

 months and even years without eating. 



* Land Tortoises. 

 Gen. 1. TESTUDO, Brogniart. 



Upper shell gibbous, supported by a solid bony frame, and 

 joined through the greater portion of its sides to the under 

 shell ; feet with short toes, united nearly to the nails, and 

 capable, as well as the head, of being withdrawn within the 

 shell ; fore feet with five nails, these behind with four, all 

 thick and conical. 



T. Grceca, Lin. The Common Tortoise. Shell hemispherical, mar- 

 bled with black and yellow, gibbous behind ; disc composed of 13 

 convex pieces, of an oblong square form, and 25 marginal ones ; 

 under shell pale yellow, of twelve pieces, with a broad blackish 



