REPT1LE>S. 



Tlie barrel of the crocodile may he dividril into two 

 parts : one external, wliicii is very wide, and cloftd on the 

 outfide by the membrane of the tympanum, and the ll<in, 

 but entirely furrounded by the bones ; and one internal, 

 which IS feparated from the former by a contradlion, and 

 which communicates with the two feneilrx, and with feme 

 cavities analogous to the madoid cell? of man, but much 

 larger. One of theie cavities is placed between the femi- 

 circular canals, and the other is direiSlod backward and out- 

 ward. The barrel is fituated towards the fuperlor part of 

 the cranium. 



The cavity of the tympanum in the tortoife is placed 

 more laterally : it is not fo wide externally ; and the con- 

 traction, wliick feparates the external part from the internal, 

 is lefs confpicuous, becaufe the projeftion, whicii it forms, 

 is rounded, and not acute, as in the crocodile. The in- 

 ternal portion is prolonged backward, in the form of a 

 large round cell : in the bottom of the cavity, oppofite to 

 the membrane of the tympanum, there is a narrow canal, in 

 which the officulum is funk, and which communicates with 

 the fencftra ovalis. The Euilachian tube is a canal of a 

 moderate length, which proceeds downward, and a little 

 backward, and terminates in the palate, behind and within 

 the articulation of the jaw. 



The Mcmbrana Tympanl and Its ojfeous Frame. — Animals 

 wliich want the barrel of the tympanum, as filhes, fala- 

 manders, &c. have no membrana tympani. That mem- 

 brane is alfo wanting in feveral reptiles that have a barrel, 33 

 the cameleon : the ikin pafles over the external aperture of 

 their ear, without undei-going any change, either in its 

 thicknefs or its ftrufture ; and the exiftc-nce of the organ of 

 hearing can only be afcertaincd by diflettion. On removing 

 the lliin, and fome portions of the mukles, we find, in lome 

 fpecies, and particularly in the flow-worm (anguis fragihs), 

 a kind of membranous cxpanfion. 



In the tortoife, the large external aperture of the barrel 

 is doled by a very thick cartilaginous plate, which is itfelf 

 covered by a fcaly Ikin, perfedlly fimilar to that of the reil 

 of the head. 



In frogs and toads, the membrana tympani is on a level 

 with the head, and the ikin that covers it becoming finer, it 

 is rendered perceptible by an oval Ipot, which is Imoother 

 than the rell of the head, and ufually of a particular 

 colour. 



In common lizards, the membrana tympani is alfo level 

 with the head, but very thin, fmooth, and tranfpareut ; for 

 at that part the ll<ui becomes as imooth and fine as the 

 cornea of the eye. 



In the crocodile, it is of the fame nature, but more funk 

 into the head, and covered by two fleihy lips, which fupply 

 the place of the external ear. 



In lizards, though the point of the cone formed by the 

 membrana tympani projefts lefs than in birds, it is alfo di- 

 refted outward, as in them. The membrane is nearly plane 

 in frogs and tortoifes. 



The membrana tympani is on a level with the adjacent 

 parts of the head, and confequently is nearly vertical in all 

 animals in \vhich its fituation is fuperficial ; but in thofe 

 whicii have it funk, its inchnation, whether confidered with 

 relation to the head itfelf, or to the external meatus, varies 

 coiifiderably. 



It inclines obliquely upward, and to one fide, in the cro- 

 codile. 



The olTeous frame, to which the membrane is attached, 

 is not marked by any prominent edge : it is interrupted 

 poilcriorly. Its great axis is vertical in the tortoife and 

 the coinmon lizards, and its anterior arch is more convex. 



In the crocodile, it is a regular oval, the great axis of which 

 is direfti'd obliquely backward. 



OJficula Auditus The frog and the toad have two ofTicuIa 



in the ear : cne fupplies the place of the malleus and the 

 incus ; it is attached to the rtiinibrana tympani by a flender 

 branch, which forms an acute angle v itli the part that pafles 

 into the barrel : that part lias the ftiape of a club ; its in- 

 ternal extremity is thethickeft, and articulates by a double 

 furface to the feeond oflicuhim, which correfponds to the 

 ftapes. The latter has a femi-elliptic form, and is applied 

 to the feneftra ovalis by its plane furface : both thefe bodies, 

 which are ofh ous in other animals, arc cartilaginous in the 

 frog and toad. 



Lizards and tortoifes rcfemble birds, in having a fingle 

 officulum with a thin hard ftalk, and an oval or triangular 

 plate (columella). It is attached to the membrane of the 

 tympanum in lizards, and particularly in the crocodile, by 

 a cartilaginous branch ; but in the tortoile, its outward ex- 

 tremity is dirrdlly implanted in the cartilaginous mafs, which 

 correfponds to the membrana tympani itielf. 



In the crocodile, the plate is an elongated ellipfis, the 

 great axis of which is fituated longitudinally. 



In the tortoife, the bone is enlarged in the form of a 

 trumpet, and is applied to the feneflra by a regularly oval 

 and concave furface. 



Serpents have an officulum, but no membrana tympani. 

 Its external extremity touches the bone that fupports the 

 lower jaw : it is furrounded by the flefh, and is applied to 

 the feneftra by a concave plate, the edges of which are ir- 

 regular. 



In the cameleon, the plate alfo reprefents the wfde end of 

 a trumpet ; its ilalk becomes cartilaginous, and is loft in 

 the flefh. 



The feneftra veftibularis of falamanders is clofcd only by 

 a fmall cartilaginous operculum, which has no ftalk, and is 

 concealed by the flcfti. 



Miifclss fif the OJfuuht. — Little is known about thefe in 

 reptiles. It appears that ferpents, cameleon";, and fala- 

 manders, are entirely deftitute of them, and that they are 

 very indiftiiift in the teftudines. Comparetti has made fome 

 refearches on this fiibjeft, but without any clear or fatis- 

 faftory refults. 



External Meatus, &c. — All parts of the ear, external to 

 the membrana tympani, are wanting in reptiles. In the 

 crocodile only is there any appearance of an external meatus, 

 the ft<in forming a kind of lip or operculum above the mem- 

 brana tympani : the latter is entirely concealed, except when 

 this coveriiio- is removed. This mull be the part mentioned 

 by Herodotus as the external ear of the crocodile, to which 

 the Egyptians attaclied rings. 



Dljlribvtion of the Nerves. — In reptiles and fifties, but 

 efpecially in the latter, we can obferve, ftill better than in 

 warm-blooded animals, the conftancy with which the 

 branches of the auditory nerve proceed to the ampullse of 

 the femi-circular canals. In reptiles it divides before it 

 pafl'es into the ofl'eous labyrinth, which it enters by feveral 

 holes. 



Organ of Touch and Integuments — It does not feem clear 

 that reptiles poflefs the fenle of touch, that is, the power of 

 recognifing, by any par-.s of their ikin, the figure, hardnefi 

 or foftnefs, rousrhnels or fmoothnefs, of bodies. To the 

 imprefiions of heat and cold, there is no doubt of their being 

 fenfible. 



In no clafs do we obferve fo much variety in the nature of 



the integuments ; the fkin is different in almoft every fpecies. 



In many the ftrufture is fo fingular, that if we judged by 



this alone, we ftiould form them into leparate claffes. What 



y a contraft 



