IlEPTILES. 



furprifed at the occurrence, becaufe all tlie funftions are 

 cither entirely fufpendeJ, or moil languidly performed." 

 Specimen, p. lO. 



Organs of Rcfpiration. — After defcribing the heart, and 

 viewing the phenomena of the circulation, we proceed to 

 the lungs, which are not only moft important parts in the 

 economy of all animals that poii'efs blood, but conftitute, 

 in the peculiarity of their Urufture and funftions, the moil 

 ftriking marks of dillinftion between reptiles and warm- 

 blooded animals. 



All reptiles breathe by means of lungs, which in their 

 bulk confiderably exceed thofe of the manunalia, while the 

 latter are as far fuperior in the abundance of their vaicular 

 ramiiications, and the wonderful minutenefs of their internal 

 fubdivifions. Thefe large, but loofe and rare veficular 

 lungs, are contained, not in a particular cavity, feparated 

 from the abdomen by a diaphragm, but, with the other 

 vifcera, in a general cavity of the body. Hence the mode 

 of refpiration is as different from that of the mammalia, as 

 the texture of the organ. 



To the general pofition, that reptiles breathe by means of 

 lungs, there is an exception in the batracian order ; in fome 

 of which (the proteus and firen) there are branchial ap- 

 pendages or gills, as well as lungs ; while in the full ftate 

 (the tadpole) of others, there is a fimilar conjunftion of 

 thefe two modifications of refpiratory apparatus. See the 

 anatomy of the tadpole, in the account of the generative 

 organs, and that of the firen and proteus, at the end of this 

 article. 



The jlir-tvles. — The trachea is not divided into bronchi in 

 the ophidian order, which have a fingle lung ; neither does 

 this divifion take place in the green lizard (lacerta agilis), 

 whofe trachea, having reached the united anterior extre- 

 mities of the two lungs, opens into each by a large orifice : 

 but it is found in almoll all the other animals of this clafs. 

 The divifion is effefted very early in the chelonians, which 

 have confequently a very (hort trachea, and long bronchi ; 

 more particularly bccaufe the latter, inftead of entering the 

 lungs direftly, firit make a turn in the cheft.. The trachea 

 is divided much later in the crocodile, where the tube is 

 bent from behind forwards, divided into bronchi, which 

 alfo run forwards, and then turn from before backwards, 

 remaining for fome time joined to each other. The bronchi 

 are extremely fhort in mod other reptiles : they begin, in 

 the batracians, immediately below the larynx. 



Reaching the lungs, the bronchi generally terminate ab- 

 ruptly by one or more large orifices, which open into the 

 cavities of thefe vifcera. This is what occurs in the ophi- 

 dians ; but in the chelonians and the crocodile, each bron- 

 chus is continued into the interior of its lung, before it ter- 

 minates. They are continued, in the teftudo grseca, into 

 the moft remote part of the lung, without undergoing any 

 fenfible change of diameter ; and they communicate with 

 the large cells compofing thefe vifcera, by ten or twelve wide 

 orifices, of which the outHnes are circular, like the com- 

 mencement of canals. In the turtles, each bronchus pene- 

 trates in like manner to the fartheft p^rt of the lung, but 

 gradually diminifhing in diameter. Their fides are pierced 

 with numerous holes, opening into the pulmonary cells. 



The relative fize of the trachea and bronchi does not ex- 

 ceed what we obferve in the mamraaha and birds, except in 

 the ophidians, where the diameter of the former is very con- 

 fiderable. Thefe air-tubes never exhibit any inequalities, 

 fuch as are feen in birds. 



They are generally compofed of complete cartilaginous 

 rings, and confequently are little fufceptible of changes in 

 fize. We mud, however, except the crocodile, in which 



animal the front end of the trachea prefents, on its upper 

 furface, a membranous interval, which is wider the nearer 

 we come to the larynx; (fee Humboldt Recueil d'Ob- 

 fervations, &c. torn. i. p. ii. of the crocodile of the 

 Orinoco ; and Geoffroy in Annales du Mufeum, tom. ii. of 

 the Nilotic fpecies) ; the cameleon, where the annuli are 

 incomplete in the lad portion of the trachea, and at its bi- 

 furcation ; and the ophidians, m whom the trachea poffeiles 

 cartilages only in one third of its circumference. Thefe car- 

 tilages are alfo viCble for a (hort fpace along the front end 

 of the lung, in a groove of its inferior furface, containing 

 alfo the pulmonary vein. The trachea, however, ceafes 

 fuddenly on touching the lung, and dilates immediately to 

 form its fac. 



In thofe reptiles which have bronchi running throughout 

 the length of the lungs, the portion of the tube, contained 

 in thefe vifcera, has only imperfeft and irregular pieces of 

 cartilage, whicli neverthelefs furround its circumference. 

 They are more thinly fcattered in the turtles, in proportion 

 as we obferve them farther back in the lung. 



This cartilaginous ftrudture of the air-tubes (the trachea 

 and bronchi) of reptiles, renders them very incapable of 

 changing their diameter. They feem entirely deftitute of 

 traiifverfe mufcular fibres ; nor do we perceive aiiy longi- 

 tudinal ones to diminifh their length. The membranous 

 trachea of the ophidians, pofleffing cartilages only in the in- 

 ferior third of its circumference, feems equally deftitute of 

 mufcular fibres. On this membrane we difcover a fine 

 white and opaque net- work, which is continued into the in- 

 terior of the lung, where its mefhes, as we (hall fee, border 

 the cells, and are formed of ftronger threads, apparently of 

 a tendinous ftrudlure, and perhaps capable of contraftion. 



Veficular StruBure of the Lungs. — We have mentioned 

 that the lungs of reptiles are very large : they are immeiife 

 in the teftudines and cameleon, and are even confiderable in 

 the native amphibia of thefe climates, if you compare their 

 relative bulk to that which they poflefs in warm-blooded 

 animals. We have juft feen that the bronchi do not divide, 

 that they do not ufually enter the lungs, but terminate ab- 

 ruptly by one or more large orifices, as foon as they have 

 reached thefe vifcera. In the batracians and faurians, the 

 lungs form two facs, varying confiderably in their form and 

 relative fize, and having their internal furface divided by 

 membranous plates into polygonal cells, in which other 

 fmaUer plates form more minute divifions. They have been 

 juftly enough compared by Blumenbach to the reticulated 

 ftrufture, in the fecond ftomach of ruminating animals. 

 Thefe cells are more numerous, fmaller, and deeper in the 

 anterior part of the fac : they become more open towards 

 the pofterior part ; and when the latter terminates in one or 

 more appendages, we fee only a net-work, with loofe and 

 extremely fine melhes. Afterwards the parietes of the pul- 

 monary fac are quite fimple, and without any divifion. 

 Such is the ftrufture in the appendices which terminate pof- 

 teriorly the lungs of the cameleon, and the agame or lacerta 

 marmorata ; and of the great bladder in which the fingle 

 lung of the ophidian order ends. 



The lungs of the falamander, the proteus, and firen, form 

 alfo fimple facs without any divifion. 



" In frogs and toads," fays- Blumenbach, " the lungs 

 are made up of polyhedric and large cells : the fame ftruc- 

 ture is obferved in the lacerta agilis and falamander. They 

 form an oblong bladder in the aquatic laceita (water 

 newts). The lung of the coluber natris forms a fingle bag 

 of large fize, hollow throughout ; and the fame ftrufture 

 feems, from the reports of anatomifts, to exift in other fer- 

 pents. (See Coiter Obf. Anat. Chir. p. 126. Charaa 



Nouvelles 



