REPTILES. 



mals : it is very tranfparcnt ; it has on ■ mufclc fituated 

 tranlvcritly, bcliiiicl the globe, which forms a tliiu tendon 

 on each fiJc of the eye, to be inferted into the free edge of 

 the third eyi'-hd. 



The fabiiiaiidcrs liave only two eye-lids, which are hori- 

 zontal, flelhy, and little moveable ; it appears that they 

 may entirely cover the eye. 



Reptiles vary as much with refpeft to their lachrymal 

 glands as to their eye-lids. 



The fea tortoifes have a very confiderable gland at the 

 pofterior angle ; it is reddilli, granulated, divided into lobes, 

 and extends under the arch which covers the temple. 



In the freth-water tortoifes we find two fmall blackifli 

 glands, which alfo exill in toads and frogs ; but their ex- 

 cretory dufts have not yet been accurately obferved. 



SL-rpents, like firties, have no gland in the eye ; they 

 have, however, a peculiar ftrutture near the eye, the office 

 of which ii not very obvious ; the following account of it 

 is given by fir Everard Hume. 



" An oval cavity is plactd at the inner angle of the eye 

 in fome ferpents, tlie opening into which is within the inner 

 angle of the eye-lid, and direfted towards the cornea. In 

 this opening there are two rows of projections, which appear 

 to form an orifice capable of dilatation and contraction. 

 Thefe cavities are lined with cuticle, which is flicd with the 

 reft of tliat integument. From the lituation of thefe oval 

 cavities, they muft be confidered as refervoirs for a fluid, 

 whicli is occalionally to be fpread over the cornea ; and 

 they may be filled by tiic falling of the dew, or the moifture 

 fhakcn off from the grafs, through which the fnake paffes." 

 Phil. Tranf. 1804, p. 75. with a figure. 



Organ of Hearing, — iiach an organ h pofTefTed by all rep- 

 tiles. Its conitruftion varies confiderably in the different 

 orders and genera : thefe varieties affecting the external or 

 accelTory parts, as the tympanum, ofTicula, &c. more than 

 the eiTential portion of the organ, its membranous labyrinth, 

 on which the auditory nerve is expanded. No reptile has 

 any external ear ; and the crocodile affords the only example 

 of a kind of external meatus. Frogs, teftudines, and moft 

 of the lizard kind, have a tympanum and Euftachian tube ; 

 but thefe parts are wanting in the falamander, and moft of 

 the ferpents. The ear of the turtle, tortoife, frog, lizards, 

 and (erpents, are defcribcd and delineated by Brunelli in 

 the Comment. Inftit. Bonon. v. 7. Comparetti has exhi- 

 bited figures of the fame fubjeft s in his Obfervationes Ana- 

 tomicx de aurc interna comparata, Patav. 1789, 4to. 

 Scarpa has given moft beautiful engravings of the ear in the 

 turtle, crocodile, green lizard, falamander, viper, and blind- 

 worm, in his Difquifitiones de Auditu et Olfaftu. 



Tie Labyrinth. — The membranous labyrinth of the ear, 

 in reptiles, is, in general, compofed, as in fifhes, of three 

 canals and a fac ; but there are fome fpecies which have an 

 additional part. 



In the falamanders, whofe ear, like that of fifhes, con- 

 fifts of the labyrinth only, the three canals are fituated above 

 the fac ; they are deprefTed fuperiorly, and form together a 

 triangle wtiicn is almoft equilateral ; each has its ampulla, 

 and the fac contains a body of the confiftence of ftarch, as 

 in the rays and {harks. 



Frogs and toads differ very little from falamanders, with 

 refpeiS; to the membranous labyrinth ; they have the fame 

 parts in the fame pofition, and their fac alfo contains one 

 amylaceous fubftance : their three canals form nearly a 

 complete circle, by their junftion with the fac. 



Crocodiles and lizards have alfo three canals, but they 

 ire larger, and each approaches nearer to a perfeft circular 

 form : the fac is fituated proportionally more within the 



head ; its membranous parietes are furniflied with feveral 

 blood-velii-ls, which are ])articularly confpicuous in the cro- 

 codile. 1 he folid parts it contains are three in number, 

 and tliey are fmaller, and even lofter, than thofe of the 

 choiidropterygious lilhes. Laftly, their labyrinth is ren- 

 dered remarkable by having an additional part to thofe we 

 liave already dclcribed : this is the firll veitige of the 

 coclilea ; it is the produdtion of the fac, in the form of a 

 cone (lightly arched ; it is diredted, under tlie cranium, to- 

 wards the middle line, and is divided into compartments, or 

 ratliL-r canals, by a double cartilaginous fcptiim ; one apart- 

 ment communicates with the fac ; the other, which is a 

 continuation of the firil, reflefted on itfelf, terminates at a 

 very fmall hole, which is clofed by a membrane that fepa- 

 rates it from the cavity of the tympanum. 



This organ is precifely fimilar to that which is found in 

 all birds. Comparetti was the firft who defcribed it in lizards. 

 It ib very large in the crocodile, and may be eafily prepared 

 from young fubjefts. 



It is more difficult to find this in the cameleon and the 

 maibl'.d lizard. A veftige of it may be obferved in the 

 ferpents. The produftion which may be compared to this 

 trumpet, or rudiment of the cochlea in the tortoife, is very 

 iimilar to the part we named the fac, ftriftly fo called, in 

 filbes ; and this refemblance confifts not only in its form, 

 but in the fmall amylaceous fubftances it contains : this 

 feems to leave no doubt of the analogy between the fac and 

 the cochlea in man, or of that between the part we call the 

 films, and the veftibule. We muft, therefore, Judge of the 

 pcrfettion of the labyrinths of thefe different ears, by the 

 degree in which the cochlea is developed. 



Tortoifes and ferpents have the femi-circular canals, like 

 other reptiles. In the tortoife they are proportionally 

 very fhort. 



The ojfeous labyrinth of reptiles refembles that of the 

 chondropterygii ; that is to fay, it envelopes the whole of 

 the membranous labyrinth, but in a manner more or lefs 

 clofely. 



In the tortoife, the feptum, which feparates the veftibule 

 from the cranium, is not ofTified ; it remains partly mem- 

 branous. The membranous femi-circular canals are much 

 fmaller than the bony cavities containing them. 



In the crocodile and other lizards, the offeous labyrinth 

 clofely embraces the membranous, or completely covers it 

 by a thin and hard lamina. 



Cavity of the Tympanum and its Appendages. — Among rep- 

 tiles, the falamander has the labyrinth completely inclofed 

 within the cranium, and deprived of all external communi- 

 cation, as in the fifhes that have fixed branchiae. But the 

 other genera of the fame order have all a feneftra, called oval, 

 fupporting an offeous plate, analogous to the bone called 

 ftapes in man. The lizard genus has another aperture, 

 clofed only by a membrane, and called feneftra rotunda. 



The barrel, or cavity of the tympanum, cannot be faid 

 to exift in ferpents : the ftalk of the plate, filling the feneftra 

 ovalis, is furrounded by the flefh, and its extremity touches 

 the Ikin, near the articulation of the lower jaw. 



In toads and frogs, the whole of its pofterior part is 

 membranous ; it communicates immediately with the back 

 of the mouth, by a large hole, which may be feen on open- 

 ing the mouth of the animal. It is very fmall, and almoft 

 entirely membranous in the pipa, in which the labyrinth is 

 coiinefted with the feneftra ovalis by only a very long 

 canal. 



It is alfo membranous pofteriorly and inferiorly in the 

 common lizards, and in the cameleon : it communicates with 

 the bottom of the palate by a fhort wide canal. 



The 



