454 CLASS REPTILIA. 



elongated, and narrow. The cerebellum is flatted, triangular, 

 and thrown back on the medulla oblongata. 



The olfactory nerves come from the anterior extremity of 

 the cerebral hemispheres ; the hole by which they are trans- 

 mitted from the cranium is double. The nasal fossse are of 

 no great extent ; they have neither cornets, nor any sinus 

 communicating with them ; they merely exhibit a few tuber- 

 cles. The nostrils are tubulous and furnished with a small 

 valve, intended to oppose the exit of air during the move- 

 ments of respiration. 



The orbits are separated from the temporal fossae, only by 

 an incomplete osseous branch, &c. (See Frogs.) 



Toads enjoy the sense of hearing. Aetius tells us that 

 they were distinguished by the ancients into deaf toads, and 

 such as could hear ; the former were regarded as venom- 

 ous ; the skin which covers the tympanum is finer than 

 that on the rest of the body. 



The tympanic box is entirely membranous in its lower 

 part. The three semi-circular canals are situated above the 

 membranous labyrinth. The labyrinthian sac contains a 

 stone of an amylaceous^ consistence, as in chondropterygian 

 fishes. 



Of the epidermis and dermis, we have already spoken 

 under the frogs, as well of everything relative to the cuticular 

 system. 



It would appear that the toads can, at will, increase the 

 excretion of the viscous humour, with which their bodies are 

 lubricated, and cause it to run out like a dew from all their 

 pores. The use of the mucus which thus invests their body 

 is manifest : it serves to defend them against the dryness of 

 the air and the heat of the sun ; it is the same with frogs. 

 One of the latter animals was destroyed by Bartholin, by first 

 rubbing the head and back with oil, and then exposing it to 

 the sun. M. Schneider has also observed the ill effect of 



