REPTILES. 



by a very flexible tail, often compofcd of articulated rings. 

 In the very elongated form of then- body, the chakides re- 

 femble ferpents, though, in other refpetts, they are true 

 faurians. The (kin is quite naked in all the batracians ; 

 they have four feet ; fome have no tail, a llout, thick 

 body, and the hind legs longer than the front ; others have 

 the fliape of a lizard, being fnrniflied with a tail, and having 

 feet of equal length. LalUy, ferpents have a very long, 

 cylindrical body, covered with fcales, and without limbs. 

 Tliefe variations of figure niuft necedarily be attended with 

 modifications in the form and pofition of organs; the in- 

 ternal arrangements will correfpond with thefe outward 

 figns. 



Although the animals of this clafs differ very confiderably 

 in outward form, as well as in tlie general bulk of their 

 bodies, tliey agree very nearly in the eilential points of their 

 organization, and more particularly in the funftions of their 

 animal economy. We may inflancc the mode of taking their 

 food ; the long abilinence of which they are capable ; their 

 oviparous generation ; the length of time, for which they can 

 bear an interruption of refpiratiou ; their tenacity of life 

 and extraordinary power of reprodnftion ; and the low tem- 

 perature of their bodies. The laft points, of animal heat 

 and reprodudtion, two exceedingly interefting fubjedls of 

 inquiry, which have been invefligated of late years with 

 great indullry, form the moll linking differences between 

 cold and warm-blooded animals ; the latter alone pofl'efling 

 that remarkable property of maintaining in themfelves a 

 temperature confiderably exceeding that of the medium in 

 which they live, while the former are diftinguifhed by the 

 wonderful extent of their power of extending or reproduc- 

 ing injured or loit prrts. 



An accurate knowledge of the flruflure of reptiles is not 

 only important from its fubferviency to the claffilic arrange- 

 ments of natural hiftory, and highly interefting from ex- 

 pofing to us new and rich fcenes in the vaft domains of 

 nature, new forms of life, and frefli modifications of organiza- 

 tion, accompanied with fingular changes of funftions already 

 famihar to us in other fhapes ; but it acquires additional in- 

 tereil from the great ufe which phyfiologilts have made of 

 different reptiles in their experimental elucidations of the hu- 

 man economy. We muft furvey in a general view the flruc- 

 ture and economy of thefe animals, and compare them with 

 thofe of ths warm-blooded dalles, before we can determine 

 how far the cunclufions, drawn from experiments on reptiles, 

 concerning the heart's motion, irritability, the aftion of the 

 nerves, the effeds of opium, &c. &c. can be transferred to 

 the human body. 



Organs concerned in the Vital FunBions. — The mouth is fitu- 

 ated at the extremity of the fnout, and direded tranfverfely. 

 If we fancy the head to be divided by a horizontal cut, ex- 

 tending from before backwards, to its very poi-terior part, 

 we (hall have a juft idea of the mouth of a reptile. The 

 cranium is very fmall in this clafs, and the head confifts almofl 

 entirely of the two jaws. The lower is articulated towards 

 the back of the head, and thus allows the opening between 

 the two mandibles, conllituting the mouth, to be very con- 

 fiderable. Alniolt all reptiles fwallow entire animals, and 

 thus require this cxtenflve opening. The margins of the 

 aperture coiifiil fimply of the maxillary arches, which are 

 not covered or enclofed by any thing deferving the name 

 of lips. In no cafe is there any maftication ; and the food 

 or prey is taken by the teeth or tongue, fo that a move- 

 able covering of the jaws, fimilar to the lips and cheeks of 

 the mammalia, is not necellary either for confining fub- 

 ftances lubjefled to the aftion of teeth as organs of maftica- 

 tion, 01 for the purpofe of reaching or feizing food. 



The horny coverings of the mandibles, completely naked, 

 and not concealed even by the Imalleft fold of (kin, form tlie 

 fides of the entrance into the mouth in the clielonian reptiles. 

 Their food confifts of marine vegetable productions, tcftacta, 

 infedts, &c. and does not require fo large an opening for 

 its introduftion, as when confiderable animals are fwallowed 

 whole. The mouth is confequently fmaller in this than in 

 either of the other orders ; and does not extend completely 

 to tiie back of the head. 



The family of tortoifes, which Geoffroy has called trio- 

 nyx, offers a remarkable exception to what we have itated 

 about the abfence of lips : they have thefe folds, and 

 a moveable probofcis at the end of the fnout. " The 

 cxillence of lips in thefe tortoifes is an anomaly, the more 

 likely to furprife u^, inafmuch as the affinity of thefe reptiles 

 to birds feems to affign a motive for the abfence of lips, and 

 alfo for the exiftence of the horny coverings of the mandi- 

 bles." Geoffroy St. Hilaire, Mem. fur les Tortues moUes ; 

 Annales du Mufeum, v. 14. pi. i. p. 9. 



In the faurians, the flit of the mouth goes to the very 

 back of the head, far behind the ear. Its appearance is very 

 formidable in the crocodile, where the hard Itrong jaw? 

 projeft into a large fnout, and are armed with (harp power- 

 ful teeth, dellitute even of gums : thefe jaws open to the 

 very back of the head, and difclofe a tremendous throat. 

 The mouth is as large proportionally in the other faurians ; 

 but their fize is too infignificant and their habits too harm- 

 lefs to allow of their infpiring that terror, which the formi- 

 dable weapons of the crocodile fo juftly caiife. The ophi- 

 dians have not only a mouth equal in its tranfverfe mea- 

 furement to the diameter of their body ; but they pofTefs alfo 

 tiie means cf enlarging this aperture, fo that they can fwal- 

 low creatures whole diameter exceeds their own. The ba- 

 tracians have an opening as large as the fize of the head will 

 allow. In the latter, as well as in the ophidian, and iroft 

 of the faurian reptiles, the integuments make a fmall fold at 

 the edge of each jaw ; thefe folds meet when ihe mouth is 

 clofcd, fo as to hide the edge of the jaws, but they pofi'efs 

 no power of motion. 



In the tadpole, in the proteus and firen, the mouth is 

 much fmaller than in the other reptiles ; and they pofTefs 

 folds more deferving the name of lips. In the former there 

 is a kind of horny apparatus within thefe lips, forming fome- 

 thing like a beak. In the fmallnefs of its mouth, and in 

 thefe hornyjaws, the tadpole is remarkably diffimilar to the 

 perfcft animal. 



The Ja-ws. — In confidering' the jaws and their mufcles, 

 the teeth, and the tongue, we muft bear in mind that thefe 

 organs are calculated merely for feizing their food, and 

 conveying it to the throat ; in no cafe does the food undergo 

 any mallication, as in the mammaha. 



No reptiles have an upper jaw moveable on the head, like 

 that of birds : the fuperior maxillary bones are in truth ar- 

 ticulated moveably with the head in ferpents, and may be 

 extended and retrained, or moved laterally, as we (hall de- 

 fcribe prefently ; but, in general, the cranium and upper 

 jaw are united into one piece, fo far as their motions are con- 

 cerned. 



Tlie moil; oppofite opinions have prevailed refpeiling the 

 crocodile, even down to the prefent time. Herodotus firft 

 obferved, that it is the only animal poflefling an upper jaw 

 moveable on the lower, which remains fixed. The fame 

 opinion was generally held by the ancients, as Ariftotle, 

 Pliny, &c. ; and feveral moderns fpeak in the fame way, as 

 Marcgrave, Marmol, Jacob=;us, Vefaliue, and the Jefuit 

 Miffionaries at Siam, who had opportunities of obferving 

 the hving animal. But the anatomifts of the Academy 'of 



Sciences 



