12 



HER FETOLOGY. 



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ceiver of an air-pump. Frogs and water-lizards have 

 livt-d.and moved with agility, many hours after having 

 been deprived of their hearts ; ana Redi, by a curious 

 but cruel experiment, proved that a land- tortoise, after 

 having the cavity ot the skull laid open, and the brain 

 dissected out, walked away with apparent unconcern ; 

 and, except that its eyes closed, and never afterwards 

 opened, it appeared for several months to enjoy life, 

 and exercise its functions nearly as before the loss of 

 the bruin. Frogs, winch were subjected to a similar 

 experiment by SpalUinzani, lived for five days. Nay, 

 a turtle has been known to live and move its limbs for 

 thirteen days after its head had been cut off. 



Not only is the body in general of reptiles thus te- 

 nacious of life, but the parts and organs that have been 

 cut off shew signs of vitality and irritability, for hours 

 and even days together. The tails of water newts 

 have exhibited very lively motions for more than ten 

 hours ; the heart of a frog has continued to palpitate, 

 when irritaU-d, for several hours after being taken from 

 the body : the head of a turtle has not only opened and 

 closed its jaws, but h:n closed upon a stick with con- 

 siderable force, two days after having been ampu- 

 tated. 



The absorbent system of reptiles has been very little 

 examined, and the investigation has scarcely extended 

 b'-yond the Chelonian order. We find that the thoracic 

 duct of turtles is double, and that the mesentery in 

 these animals abounds with lacteal*. Numerous lym- 

 phatics are seen running in a longitudinal direction, 

 both on the superficial and central coats of the intes- 

 tines ; but it is not certain that these animals possess 

 lymphatic glands. 



If we may judge from the little waste that takes 

 place in the body of reptiles during a long abstinence, 

 and wliile in the torpid state, it would seem that their 

 absorbent system possesses less activity than that of 

 most other auimals. 



CHAP. V. 



Of Respiration and Voice in Reptiles. 



THE lungs of reptiles are proportionally much larger 

 than those of quadrupeds and birds, and they are also of 

 a much looser texture ; their structure is most compli- 

 cated in the Chelonian order, in which they are of a 

 uniform texture, but the air vesicles are very large. In 

 the Saurian order, the lungs form two large vesicular 

 bags, one on each side tle heart, and have their inter- 

 nal substance divided by membranous plates into nu- 

 merous polygonal cells, which are again subdivided in. 

 to smaller. All the Batracian order have lungs, which 

 resemble those of most of the Saurians in largeness and 

 simplicity; but in the tadpole state, they have also gills, 

 which disappear in the perfect animal, except in two 

 tribes, in which they are permanent. 



I-ungs. I" H, the lungs float loose with the other viscera in 



the same cavity, and appear to have no innate contrac- 

 tile power. 



The windpipe, except in one or two instances, di- 

 vides into branches or bronchi, before it reaches the 

 lungs ; but this division takes place nearer the head 

 in some tribes than in others. In the Chelonians, it 

 commences very early, while in the crocodile the tra- 

 chea continues undivided for a considerable extent. In 

 general, however, the bronchi are very short, and in 

 t instances they terminate abruptly jjj the lungs. 



The extent of the lungs is greatest in the Chelonians, Anatomy 

 in whom they reach along the whole length of the an <{ 

 back. The lungs of reptiles are supplied with blood 

 by the pulmonary arteries, there being in general no 

 bronchial vessels. 



The gills or branchiae of tadpoles, and of the pro- Branchiae. 

 teus and siren, resemble the gills of fishes in their ge- 

 neral structure, but are not, like them, inclosed within 

 a particular covering, but hang loose and floating on 

 each side of the neck. They form three or four rows 

 of small tufts or fringes, supported by small cartilagi- 

 nous arches ; and these arches are articulated on one 

 side behind the cranium, while on the other they are 

 united to a bone re-.embling the os hyoides. They have 

 between the rows intervals, by which the water in 

 which the animal floats is freely admitted to the 

 mouth. The branchiae of the siren consists of three 

 tutts. 



The spongy texture and little vascularity of the lungs Respiration. 

 in reptiles, enable them to take in a greater quan- 

 tity of air than other animals at a single inspiration, 

 and this capacity appears to be increased by the expan- 

 sive power of the air cells. It is remarkable, that rep- 

 tiles not only receive air into the lungs in the ordinary 

 way of inspiration, but swallow it by the mouth, in 

 which action they are assisted by the muscles of the 

 throat. In fact, it is only by deglutition that the Che. 

 lonians inspire, and in expiration the animals of this 

 order employ chiefly two pairs of muscles, situated in 

 two layers near the tail, between the shield and breast- 

 plate. In the Saurians, the mechanism of respiration is 

 executed chiefly by the abdominal muscles, and by those 

 which move the ribs. 



From the large quantity of air which reptiles can 

 inspire at once, there is the less occasion for frequent 

 respiration ; and, accordingly, in these animals, the 

 breathing 'is remarkably slow. It is least slow in the 

 Chelonian tribes, and it appears to be slowest when the 

 animals are asleep. What is most remarkable, how- 

 ever, in the respiration of reptiles, is the power they 

 possess of suspending respiration. Tortoises have been 

 known to live more than a month with their jaws close- 

 ly tied, and their nostrils stopped with wax ; and there 

 seems little reason to doubt the remarkable instances 

 that are on record, of toads being found alive in the 

 trunks of trees and blocks of solid stone, where the 

 function of respiration must have been suspended for 

 years together. It also appears that reptiles can live 

 for a longer time uninjured in deoxygenatecl or impure 

 air than other animals ; a circumstance that is explain- 

 ed on similar principles. This continued vitality in vi- 

 tiated air, has its limits however ; for it is found, that 

 when these animals are confined in atmospheric air, 

 they cease to exist when the oxygenous portion is ex- 

 pended. 



The changes produced on atmospheric air by the res- 

 piration of reptiles, are similar to those produced by 

 the breathing of other animals, viz. the consumption 

 of oxygen and formation of carbonic acid. On this 

 subject we may refer our readers to Mr Ellis's Inquiry 

 into the change* produced on Atmospheric Air, published 

 in 1807, and Further Inquiry in 1811, in which the 

 experiments and observations made by the ingenious 

 author, and collected by him from former writers, are 

 fully and satisfactorily detailed. 



Intimately connected with the function of respira- Vital lict. 

 tion, is the vital heat of animals. We have already 

 seen that this in reptiles is very low. It appears, how- 



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