ORGANIZATIONOFREPTILES. 37 



analogous to the incus and malleus:* there is a similar arrangement in Toads, 

 though the chain of bones is longer, and both are well disposed to carry impres- 

 sions to the labyrinth. The membrane and cavity of the tympanum do not exist 

 at all in the Salamanders; nor have they an Eustachian tube openmg into the fauces. 

 The labyrinth or internal ear consists of three semicircular canals, and a sac 

 containing a substance resembling starch in appearance; in some there is a rudi- 

 ment of a cochlea, as in the Chelonia, which is still more distinct in some of the 

 Saurian Reptiles; in those consequently the organ of hearing must be more delicate 

 than where the cochlea is wanting. In the Salamander, another and very different 

 arrangement of parts is observed; the labyrinth is completely closed, having no 

 external communication whatever. From this structure it results, that the sense 

 of hearing must be much less perfect in Reptiles than in the Mammalia and Birds; 

 they cannot distinguish delicate sounds, nor can they be made like the Birds to 

 imitate them. 



Smell. — The organ of smell is less developed in Reptiles than in the Mammalia 

 and Birds; nor is it apparently employed in selecting food, as in those classes, or 

 even as in the Fishes, where the olfactory organ is intimately connected with the 

 functions of nutrition and respiration. The nasal cavities are extremely simple 

 in their arrangement, and of very limited extent, lined with a pituitary membrane, 

 sometimes folded, on which the olfactory nerve is distributed. 



The external nares are small, and placed near the snout; in some they are close 

 together, in others, farther apart; in most, the orifices can be contracted, dilated, 

 or completely closed in respiration. The posterior nares open but a short distance 

 behind the anterior; in the Chelonia they are situated about the middle of the 

 palate, and still further back in the Alligator. In Serpents, the canals are broader, 



*Pohl. Exposit. Organ. Audit., p. 12, as quoted by Gore in his excellent translation of 

 Carus's Comparative Anatomy says, there is but a single bone similar to the columella of the 

 Chelonia in the tympanal cavity of Frogs. Blainville, on the contrary, describes three of 

 these bones. Loc. cit., p. 539. 



