ORGAN OF HEARING. W 



example, being very small. The three ossicles can still be recog- 

 nised in the Rodentia, e. g. the Squirrel. The handle of the malleus 

 is especially subject to variation ; in the Carnivora it is very long, 

 in the Sloth broad with a projecting ridge ; in the Rodentia it is fre- 

 quently formed like the blade of a knife. In Chrysocloris a peculiar 

 clavate bone is found lying between the malleus and incus. Small 

 animals not unfrequently possess very clumsily shaped ossicles, as 

 is the case in a remarkable degree in the malleus of the Hedge- 

 hog. The stapes exhibits very interesting modifications of form. 

 Without bearing any relation to the position of the animal in 

 the system, it presents, for example, in the higher Apes, the 

 Elephant, Mole, Hedgehog, Ox, only slight variations from the 

 human form, its opening being larger or smaller, its branches 

 equal or unequal. In some Rodentia and Insectivora, as in the 

 Squirrel, the Marmot, the Mole, a branch of the carotid, namely, 

 the trunk of the arteria opthalmica and maxillaris, and in Chei- 

 roptera, the art. meningea media, pass through the stapes and 

 the tympanic cavity ; the artery between the branches of the stapes 

 is surrounded by a bony tube which serves as a kind of bolt 

 (pessulus) upon which the stapes rides, and is thus prevented 

 from entering too far into tfre very large foramen ovale. In the 

 Seal and other animals the branches of the stapes are very thick, 

 and the opening therefore very small ; the latter indeed disappears 

 completely in the Walrus, the Dolphin and the Whale. Imperfo- 

 rate and rod-shaped, the stapes of the Ornithorynchus resembles 

 the columella of Birds, and a similar transition of form is shown in 

 the Sloth and Kangaroo, and, as appears from recent researches, 

 in the Marsupiata generally. The muscles of the ossicles appear 

 to be always two in number, as in Man, the tensor tympani and sta- 

 pedius. In the Horse and Ox, there is frequently found a sesamoid 

 bone in the stapedius muscle. The cells which in Man are found 

 in the Mastoid process of the temporal bone, are present also in the 

 Apes, but they frequently disappear along with that process, which 

 is often represented by an apophysis of the occipital bone ; in some 

 instances, however, small cells extend also into the squamous and 

 even the jugal portions of the temporal. 



External to the membrana tympani there lies in nearly all the 

 Mammalia, excepting the Cetacea, the bony meatus, which differs in 

 length, width, and direction. Attached to it is a trumpet-shaped 

 cartilage, the concha of the ear, which is wanting only in a few 

 Mammalia, namely, such as live in water or under the earth, as in 



