ORGANS OF HEARING. 155 



cartilaginous ring, upon which the membrana tympani, uncovered 

 from without, is stretched. The fenestra ovalis is closed by a car- 

 tilaginous, slightly concave operculum, upon which the broad end of 

 the columella rests, while to its outer extremity a small cartilage 

 is united, the swollen head of which is fixed upon the membrana 

 tympani ; the two Eustachian tubes open into the cavity of the 

 pharynx, and occasionally in the middle of the latter by a common 

 aperture. In the Chelonia and Sauria the tympanic cavity re- 

 ceives a partly bony, partly membranous Eustachian tube, which 

 is mostly very short and broad in the Sauria ; several of the latter 

 have also the membrana tympani covered by skin and muscle. 

 The fenestra ovalis is closed by an operculum, upon which rests the 

 columella, and is united to the membrana tympani by a small car- 

 tilaginous frequently divided body, that presents a discoidal form 

 in the Chelonia. If we compare this chain of auditory ossicles 

 with those of the Mammalia, the small cartilage united to the tym- 

 panic membrane will be found to agree with the malleus, the columella 

 with the incus, and the operculum with the stapes, if not in form, at 

 least in function. Two muscles are found in the internal ear of Rep- 

 tiles, namely, a tensor tympani, and a stapedius. 



A variety of specialities belonging to the auditory apparatus oc- 

 cur in this diversely constructed class ; of these the following are 

 perhaps the most important to be mentioned. The operculum is 

 found in Coecilia, Amphiuma, Siren, and Tortrix, and a small col- 

 umella, such as occurs also in the true Serpents, in Amphisboena. 

 Typhlops and Rhinophis have no auditory ossicles. In the Sala- 

 mander there is situated a membrane upon the fenestra ovalis, be- 

 neath the operculum, and a short canal conducts to the vestibule. 

 The Bufo igneus, and Rana cultripes Cuv., perfectly resemble the 

 Salamanders, in the absence of a tympanic cavity, and they have 

 also, like Pipa, only a single opening within the pharynx for the two 

 Eustachian tubes. In the Tortoises, the incomplete canal of the 

 Eustachian tubes is seen at the base of the sphenoid bone, made 

 up inferiorly by membrane ; in several, as in the genus Chelonia, 

 the columella is lodged in a posterior excavation of the os quad- 

 ratum, which receives the membrana tympani, and in Emys expansa 

 is in the form of a foramen. The columella is moved by a single 

 muscle. In Chameleo, Anguis, Acontias (in which last the colu- 

 mella even is wanting), and partly in Pseudopus, the membrana 

 tympani is covered by muscles and integument, but is freely ex^ 

 posed on the contrary in Ophisaurus, while in Chirotes the whole 



