C H E L O N I A. 



plants, and all grow freely in any <oil. They are 

 easily propagated by cuttings, placed under a hand- 

 glass. 



CHELONIA. The first order of reptiles in 

 Cuvier's arrangement. Some of them are land animals, 

 and others aquatic ; the former being known by the 

 general name of tortoises, and the latter by that of 

 turtles. They are all four-footed animals, or quad- 

 rupeds ; and they are encased in a coat of armour, 

 usually called a shell, and which adheres to the ster- 

 num and the ribs. 



They have the heart with two auricles, but only 

 one ventricle, though the latter is divided into two 

 chambers or cells, by an incomplete partition, which 

 admits of a communication between the one and the 

 other. The blood, which returns from the circulation 

 over the body, is received into the right auricles of 

 the heart, and that from the lungs into the left ; but 

 owing to the imperfect division of the ventricle, the 

 circulation is incomplete, as the blood which has 

 undergone the action of the air in passing through 

 the lungs, is in part mingled with that which comes 

 from the body, and the mixture is returned to the 

 system, so that only a portion of even that which 

 passes through the heart is subjected to the renova- 

 ting influence of the air in the lungs. 



In all animals, even those which have the double 

 heart most perfect, only a limited portion of the blood 

 passes through the heart at each pulsation ; and the 

 inferior vertebrated animals, which have a slow cir- 

 culation and low temperature, have only a portion of 

 that which passes through the heart sent to the lungs ; 

 this portion being less and less in proportion as the 

 general action of the system is more languid. 



The structure of a chelonian reptile can be per- 

 haps best explained by first attending to the most 

 striking part of its external appearance, the double 

 buckler in which its body is encased. This princi- 

 pally consists of two parts, a spinal and a sternal 

 one ; the first the shield on the buck, and the second 

 the breast-plate on the under part of the body. Both 

 of these consist of a number of pieces, which varies 

 in different species ; and the forms of the plates, and 

 the modes of their junction with each other, are the 

 foundations of some of the trivial characters. 



A row of these plates ranges down the back of the 

 animal, and there are others ranged along the sides 

 of these which, with them, form the disc of the shield. 

 Of these there are sometimes as many as eight pairs ; 

 and towards the margins of the breast-plates they 

 are surrounded by others, usually about from twenty- 

 one to twenty-five, which form the margin of the 

 shield. They are more irregular in their forms than 

 the plates which compose the disc, and are generally 

 oblong ; the lateral plates are united by sutures to 

 each other, and also to the dorsal plates, which last 

 are fastened, but not soldered, to the vertebra. When 

 the different plates or pieces which form the shield, 

 rise in a sort of ridge in the middle, they are said to 

 be cariuated, or keeled ; when they are depressed in 

 the middle, they are said to be fun-aired ; when they 

 rise uniformly to the middle, they are called convex 

 or sub-convex, according to the degree of elevation ; 

 when they lie over each other like slates on a roof, 

 they are imbricated ; and when they have the mar- 

 gins toothed or jagged, they are serrate d. The piece 

 which form the breast-plate or estcrnal buckler, are 

 usually about nine in number. They are more or 

 less firmly attached to the marginal plates of the 



shield along the side<. : ; and in general none of the 

 larts which form these two bucklers, or are attached 

 ;o them, have any motion. 



There is one opening between the shield and 

 jreast-plate anteriorly, through which the head and 

 'ore extremities of the animal are projected ; and 

 another at the opposite end, for the posterior extre- 

 mities and the tail. 



The anterior extremity of the blade-bone is arti- 

 culated with the shield , and there is a connexion 

 with the opposite extremity, and the breast-plate is 

 united by a connexion which bears some slight 

 resemblance to a clavicle. Thus the extremities, 

 which bear the weight of these animals, are not arti- 

 culated directly on the spinal column, any more than 

 they are in the higher orders of vertebraied animals. 

 In some species the terminal plates, or pieces of the 

 breast-plate, are capable of a slight motion, so as 

 completely to shut in the head and extremities, and 

 protect them from the attacks of every enemy except 

 man. Those which have this structure and motion 

 of the shell are called " box tortoises." 



In the greater number of the species, the motion 

 of the extremities is exceedingly slow ; but the power 

 of moving other bodies is great in proportion to the 

 slowness of the rate, for one of the larger land tortoises 

 can get along at its sluggish pace, with the weight of 

 two or three men standing upon its back. The vertebra 1 

 of the neck are beautifully articulated ; and although 

 the range of space over which it is capable of moving 

 is very limited, there is perhaps no animal which 

 commands with so much certainty and steadiness 

 the space over which it can move. 



There is a sort of frame-work of osseous pieces, 

 which bears some resemblance to the sternal or carti- 

 laginous portion of the ribs ; but this has no motion, 

 nor indeed is there motion in any part of the ani- 

 mals, except in the head and neck, the tail and the 

 extremities. 



The osseous portion of the chelonia is immediately 

 covered by the integuments, the scaly plates on the 

 skin, without any intervening muscles, which are all 

 placed on the inside, so that in some respects these 

 appear to be animals turned inside out, or at all 

 events with the substantial part of the skeleton without 

 side the organs of motion ; and they are thus in some 

 respects intermediate between the vertebrated and 

 articulated animals. There is even a resemblance to 

 birds, though a very slight one, in the articulation of 

 the anterior extremity : there is a large bony haunch 

 which extends backwards, from the articulation of 

 what may be termed the humeral joint, and which, 

 in form and position, bears some resemblance to the 

 coracoid bone in the feathered tribes, only it does not 

 abut on any solid support at its posterior extremity, 

 either on the breast-plate, or on the bony frame-work 

 above alluded to. It appears merely to afford the 

 shoulder a more firm imbedment than it could other- 

 wise have. 



The lungs of the chelonia are contained in the same 

 cavity with the rest of the viscera ; as is the case in 

 all reptiles, they extend into the abdomen, but they 

 are separated from the abdominal viscera, properly so 

 called, by a duplicature of the peritoneum. In con- 

 sequence of the structure of the shelly covering, 

 which precludes the possibility of breathing in the 

 ordinary manner, by the action of an elastic thorax 

 and a diaphragm, the breathing of the chelonia is very 

 peculiar, and has more resemblance to a sort o*" 



