REPTILES. 



common lizard : but they are very different in tliofc whofe 

 lower jaw coiififts of two dilUnft pieces : we fliall defcribe 

 them in the rattlefnake. 



Here the niufcles of the lower jaw are concealed in the 

 lips, and go round the mouth on each fide. That which 

 forms the anterior edge of the commiirure of the lips is the 

 ftrongell, and feems to hold the place of the mafleter. It 

 arifes by firm aponeurofes from the tendinous flicath, which 

 contains the venomous gland. Its fibres form a confiderable 

 cord, which conftitutes the whole thicknefs of the lower lip, 

 and are inferted in the upper edge of the inferior maxillary 

 branch for almoft two-tiiirds of its length. 



The mufcle immediately behind is analogous to the tem- 

 poral, and is much flenderer than the preceding. It is a 

 mufcular fafciculus, of which the fuperior extremity is fixed 

 to the temporal excavation behind the orbit, and the in- 

 ferior, after going backwards beliind the commifTure, is 

 confounded with the infertion of the lall mufcle. It is 

 obvious that the contraclion of thefe two mufcles muft 

 approximate the jaws, and thus clofe the mouth. 



In the commiiTure of the lips, and behind the two laft 

 mufcles, we fee another refembhng them in form, but much 

 (horter. It occupies the inferior part of the os quadratum, 

 and about the pofterior third of the javif, at tlie outer edge 

 of the denta! canal. It is an acceffory mufcle to the tem- 

 poral and mafleter. 



The mufcle correfponding to the digaftricus occupies the 

 whole length of the back of the os quadratum, and ter- 

 minates at the poilerior apophyiis of the maxillary branch 

 beyond and behind its articulation. 



The mufcles moving the upper jaw are more numerous. 

 One arifes, by aponeurotic fibres, from the capfule of the 

 joint, between the maxillary branch and the os quadratum, 

 and pailes forwards and upwards towards the flieath of the 

 venomous teeth, being partly expended on that fhcath, and 

 on the pofterior apophyfis of the fuperior maxillary bone. 

 Its ufe is evidently to draw down the venomous teeth, when 

 they have been elevated. 



Two other mufcles aft on the pterygoid and palatine 

 branches. Both are fi uated between the middle line of the 

 bafis cranii and the palatine arches. The lovver, lituated 

 immediately under the (kin in the palatine foffa, is a plane 

 of elongated fibres, occupying the whole middle line of the 

 cranium, and going backwards to the internal furface of 

 the bony pterygoid plate, which it will carry inwards and 

 forwards, fo as to protrude the fuperior maxillary bone, 

 and elevate the venomous fangs, at the fame time contraft- 

 ing the mouth by the approximation of the two internal 

 arches. 



The other mufcle, flenderer, and placed above the pre- 

 ceding, towards the bafis of the fliull, extends from the 

 anterior portion of the palatine arch, and the whole length 

 of this arch, to the middle of the bafis 'cranii, crofling the 

 direction of the laft mufcle, on which it is placed. When 

 it contrafts, it carries backwards the whole mafs of the 

 upper jaw, at the fame time approximating its two branches. 



By means of this mechanifm, ferpents can twill their 

 mouths in feizing objefts, and dilate them extraordinarily, 

 fo as to fwallow animals larger than themfelves. Their 

 teeth ferve merely for holding their prey ; and the mufcles 

 moving the bones, in which thefe teeth are implanted, can- 

 not move them in fuch a way as would be neceffary for 

 maftication, but merely deprefs, elevate, approximate, fepa- 

 rate, protraft, and retraft them. 



Lac^pede thus defcribes the motions of the jaws in fer- 

 pents. " While the teeth of one fide are fixed in the prey 

 which the animal has feized, and are therefore motionlefs, 



thofe of the other fide are carried forwards penetrate ilie 

 animal, drag it tov/ards the throat, and there fix it in 

 their turn ; when the oppofite ones arc again advanced to 

 repeat the fame procefs on their fide. By thefe repeated 

 alternate motions of the two fides of the jaws, combined 

 with their lateral expanfion, ferpents are enabled gradually 

 to fwallow animals of a diameter exceeding their own." 

 Hift. Nat. des Serpens. 



T/je Teeth. —Their ftrufture has nothing peculiar in rep- 

 tiles. The bone is compact and hard ; the enamel thin ; 

 and, as they are always thin, there is none of the third fub- 

 ftance called by Cuvierthe cement. We are not acquainted 

 with any fafts concerning the fucceflion of the teeth in 

 reptiles ; — w^hcther they have two ftts, or that the firft 

 grow conftantly, or that the jaws are elongated ante- 

 riorly, &c. The crocodile forms an exception to this re- 

 mark ; we are indebted to Cuvier for a very interelting ac- 

 count of the fucceflion of their teeth, wliich we (hall fl.ate 

 prefently. 



The chelonian reptiles, like birds, have no teeth, pro- 

 perly fo called: the horny fubftance encafing their jaws, and 

 fupplying the place of teeth, will be defcribed at the end of 

 this account of the teeth of reptiles. 



The faurian, ophidian, and batracian reptiles may be 

 compared to the cetacea ; as they do not mafticate their 

 prey, the teeth are calculated merely to hold, and not to 

 divide it : hence they have much lefs influence on their 

 economy than thofe of viviparous quadrupeds. They ac- 

 cord, however, tolerably with the natural genera and fub- 

 genera. 



Tiiey are almoft always the fame in all parts of the jaw, 

 fo that they admit of divifion into different dalles, ac- 

 cording to their configuration, only in very few fpecies. 



Sometimes they are attached to the two jaws only, as in 

 the mammalia : this is the cafe with the faurians (excepting 

 only the iguana, which has palatine as well as maxillary 

 teeth) ; lometimes they are implanted alfo in the palate, as 

 in the ophidians, with the fiugle exception of the amphil- 

 baena. Their number is of lefs importance ; firft, becaufe 

 it is confiderable, and > ot accurately determined ; fecondly, 

 becaufe they fall out without any hitherto afcertained re- 

 gularity, either in fituation or time. 



Teet/} of the Saurians. — In the crocodile the enamel is more 

 or lels ihiated longitudinally. The upper and lower teeth 

 crofs when the jaws are fliut. They are all conical, hollow, 

 generally a little curved, and marked with two longitudinal 

 projecting lines ; an anterior and a pofterior one. The five 

 or (\\ pofterior teeth on each fide are more obtufe and com- 

 prelled than the others. 



In a living crocodile, which Perrault obferved at Ver- 

 failles in 1681, he found that all tlie teeth were flightly 

 bent towards the throat, and that this curvature was the 

 moft confpicuous in thofe near the end of the fnout. When 

 the jaws were drawn together, the teeth of each jaw pafled 

 into the intervals between thofe of the other, fo that an 

 uninterrupted feries was vifible, as there are no lips to hide 

 them. He fays further, that the points of the upper teeth 

 entered into excavations of the lower jaw. 



The following account is derived from Cuvier's Obf. fur 

 I'Ofteologie des Crocodiles vivans, in the icth volume of 

 the Ann. du Muf. " Tke number of the teeth does not 

 chnnge with the age of the animal : a crocodile quitting the 

 egg has the fame number as one twenty feet long. I have 

 afcertained this faft in a feries of heads from an inch to 

 two feet long. The back teeth may be a little concealed 

 by the fltin of the gums. The interior is always hollow, 



although 



