IIEPTII.KS. 



is a point, in which ihcy exceed thol> of the human fubject, 

 and of lliL- other mamiiiaUa ; namely, a particular kind ot 

 tone, or energy, by virtue of which, even when the chell is 

 opened, and they are expofed to the external air, they are 

 Hill diltended and fuppurt themfelves, while thole of tlie 

 mammalia, when the llernum is removed, and the thoracic 

 cavities expofed, uUuw the air to rufh out, and coUapfe. 

 (See Morgagni Adverfar. Anat. 5, 29, and tiie elegant ex- 

 periments on the tortoife by the Parifian academicians ; 

 Hift, des Animaux, part ii. p. 194.) It is even alferted, 

 that when the lung is comprell'ed in a tortoife opened ahve, 

 it has the power of dillending itfelf again. (Coiter Obi. 

 Anat. Chir. p. 127.) A tortoife, from whom the lower 

 ihell had been removed, the thorax conlequently being 

 opened, and the lungs expofed to the air, furvived for feven 

 days. (Hill, dco Animaux, jull quoted.) The caufe of 

 thefe phenomena can only be found in the peculiar vital pro- 

 perties of the lungs ; as it cannot be referred to contractihty, 

 irritability, or nervous influence. 1 have never been able 

 to deleft, in the lungs of amphibia, any more appearance 

 of truly mufcular texture, than in thofe of the mammalia, 

 to which a modern author has too liberally afligned irrita- 

 bility. (Varnier in Hill, de la Soc. de Medeciue, 1779.) 

 The defign of this peculiar vitality in the lungs of amphi- 

 bia will appear very obvious, when wcconfider that it exills 

 in animals who have a very impcrfeft bony thorax, or none 

 at all, or one m gre.it meafure incapable of motion. Such is 

 the cafe with frogs and toads, who are entirely dellitute of 

 ribs ; with nearly all the tortoifes and turtles (excepting, 

 perliaps, a few of the foft fpecics), in whom the whole co- 

 verings of the trunk are immoveable, fo that neither the 

 thorax, nor the abdominal mufcles, can execute thofe mo- 

 tions in refpiration, which they perform in warm-blooded 

 animals." 



Mecbanifm of Rffpirattoh. — In this, as well as in other 

 points, the feveral orders of reptiles differ from each other. 

 The chelonians, whofe ribs are in the form of large odeous 

 plates, confolidated to each other, and motionlefs, are, in 

 effeft, like the batracians, fome of which have no ribs at all, 

 while in others thefe bones are too fliort, and too little luf- 

 ceptible of motion, to be capable of afiilting in the procefs 

 of refpiration. In all thefe animals, then, we can no longer 

 regard thefe bones as the principal agents ot the refpiratory 

 funftion. They alfo want the diaphragm, like all other rep- 

 tiles. Confequently the mechanifm of refpiration differs 

 in them, in its ellential points, from that delcribed in the 

 article Lungs, which belongs to the whole clafs of mam- 

 malia, where the refpiratory organs, inclofed in a peculiar 

 cavity, follow all the motions of that cavity. 



In faft, it is now well afcertained, that tlie batracian re-p- 

 u\e% f-walloiu air into their lungs. They clofe the mouth, and 

 dilate the throat, when the external air, rufhing through the 

 nollrils, fills the empty fpace. The fterno-hyoidei, carry- 

 ing the OS hyoides downwards and backwards, are the great 

 agents in this dilatation of the throat : the coraco-hyoidei 

 aflill them. When the former mufcles are cut, refpiration 

 eeafes. The elevation of the os hyoides, pi-incip.illy by the 

 ftylo-hyoidei, contraAs the cavity of the throat, and drives 

 the air into the lungs. The efcape of this air from the 

 throat by the nofe is, no doubt, fays Cuvier, prevented by a 

 talve ; but no fuch ilrufture has been demonilrated. The 

 aftion of the abdominal mufcles, and perhaps a contraftile 

 power of the lungs themfelves, expel the air from thefe 

 vifcera in expiration. Tow-nfon, who has inveif igated this 

 fubjeft moft attentively ( fee his Obfervatione s Phyfiologicse de 

 Refpiratione Amphibiorum, 8vo. Vienna, 1 798, with figures ; 

 alfo tranflated into Englifti in his " Trads,") obferves, that 



he docs not know wliether the mufcles extending fronv 

 tlie glottis to the pubea (liould be called oblique or uol 

 They furround the lungs in their whole extent, and have a 

 coldiderable comprefiTive force. Tiiey probably confill oi 

 different mufcles ; tiicir fibres extend more or lofs tranfverfely, 

 and are therefore well calculated to produce the effect he has 

 aliigned to them. He ilates that he has always feen the 

 frog's lungs coUapfe when the glottis was opened, whether 

 the -luimal was dead or alive. 



If the mufcles and the membrane of the throat are re- 

 moved, leaving only the fterno-hyoidei, the motions of the 

 OS hyoides, whicli take place in refpiration, are continued, 

 although refpiration itfelf is deltroyed. The latter effect is 

 a confequence of the deftruftion of the throat ; no cavity 

 can now be formed to receive the air, which the animal fwal- 

 lows in breathing. The os hyoides, however, is alternately 

 deprelled and elev.-ited, and the glottis continues to open and 

 ihut, but the lungs are permanently coUapfed. If all the 

 mufcles employed in moving the os hyoides are cut, the 

 glottis, whofe mufcles are entire, is opened and clofed. In 

 the fame way, when warm-blooded animals have received a 

 large wound in the chell, they make vain efforts to breathe, 

 and to get rid of the painful fenfation of fuffocation. 



It will appear, from the preceding defcription, that the 

 frog's mouth muff be fliut w hen he breathes ; and this is fo 

 llriclly neceffary, that the animal perifhes from fuffocation, 

 if his mouth be kept open. Herholdt and Rafn aflerted 

 this in a communication to the Academy of Sciences at Co- 

 penhagen, and the point has been verified by Cuvier and Du- 

 meril. See Bulletin de la Societe Philomatique, N^ 30, 

 an. 7. p. 43. 



Tiie fame mechanifm is employed in the chelonians. De- 

 glutition is the only means they can employ for introducing 

 air into their lungs. Having the mouth clofed, they alter- 

 nately contradl and dilate the throat, like- the batracians, 

 and by the fame powers. The air is expelled from the lungs 

 by two pairs of mufcles, analogous to the abdominal 

 mufcles. Thefe fill the pollerior interval between the iter- 

 num and the back fliell, in which the pofterior extremities 

 are folded when at reft. We perceive, at this part, in the 

 chelonians, thofe motions of contraftion and dilatation, 

 which are obferved over the whole abdomen in the mam- 

 malia. 



The firft, or outer pair, correfpond to the external oblique 

 mufcles : it is attached to the whole anterior edge of the 

 pelvis, to the back and front fhell, and is extended in the 

 whole pofterior interval of thefe parts. The internal mufcle 

 conS.fts of tranfverfe fibres, attached above to the pofterior 

 half of the back fhell, near the vertebrae, defcending on the 

 outfide of the vifcera, inclofing them, and terminating be- 

 low in a middle aponeurofis. The latter palles partly under 

 the bladder, and will ferve to evacuate that organ when the 

 mufcles contraft. They cotnprefs immediately only a 

 fmall portion of the lungs ; but they prcfs ftrongly on the 

 abdominal vifcera, and through the latter on the lungs, fo 

 as to expel the air. Perhaps, too, the lungs may contraft 

 by fome powers of their own. 



The mechanifm of refpiration, in the faurians and ophi- 

 dians, is very analogous to that of birds, inafmuch as this 

 funftion is particularly executed by the motions of the ribs 

 and of the abdominal mufcles. In moft of the faurians, the 

 ribs are perfedlly fimilar to thofe of birds, confilling of two 

 portions, united by a moveable articulation, and forming an 

 angle, which is opened in infpiration, and clofed in expira- 

 tion. The mufcles which put them in motion are analogous 

 to thofe employed for the fame purpofe in birds. 



The ribs of ferpents, forming fimple arcs, compofed 



merelj 



