850 THE APPARATUS OF THE SENSES. 



3. Adipose Cushion of the External Ear. 



This cushion, which is never absent, even in the most emaciated animals, 

 envelops the base of the concha in front, inwardly, and posteriorly. It 

 facilitates the movements of that organ. 



4. Integuments of the External Ear. 



The skin covering the concha is covered with fine close hairs. That 

 lining its interior is very thin and vascular, adheres closely to the cartilage, 

 and is furnished with long silky hairs, to prevent the entrance of dust into 

 the ear. 



DIFFERENTIAL CHARACTERS IN THE AUDITORY APPARATUS OF OTHER THAN SOLIPED 



ANIMALS. 



There are no notable differences in the internal ear. 



In the middle ear, there are some modifications, either in the bones or accessory parts. 

 In Ruminants, the auditory bones are like those of the Horse, except that the handle of 

 the malleus is more curved, and the body of the incus is longer. In the Dog, the handle 

 of the malleus is covered with small, pointed processes, and the branches of the stapes are 

 long and thick. In the Pig, the branches of the latter are slight and inflected, and the 

 base is wide and thin : in a word, the stapes of this animal bears no resemblance to a 

 stirrup ; the malleus is very much inflected forwards. In the last two animals, no osseous 

 nucleus is found in the tendon of the stapedian muscle. 



It is needless to say that the fenestra ovalis varies with the base of the stapes. (The 

 absence of the mastoid cells in the Sheep and Goat has been already noted.) 



The Eustachian tube exists in all the animals, but the guttural pouches are only 

 found in Solipeds. 



In the external ear, the conchal cartilage varies much in shape. It is thin, inclined 

 outwards, and widely opened in Ruminants. In the Pig, it differs a little, according to 

 breed, though it is always much developed, sometimes erect, but most frequently 

 drooping. It is always short, pointed, erect, and open in front, in the Cat. (In this 

 animal a small duplicature of the external margin of the concha is often seen.) In Birds, 

 the external ear is limited to the auditory canal. 



(The differences in the muscular arrangement have been noted elsewhere.) 



COMPARISON BETWEEN THE AUDITORY APPARATUS IN MAN AND THAT OF ANIMALS. 



There is nothing to be said regarding the internal ear. The middle ear comprises 

 the same parts as that of mammifers other than Solipeds. The handle of the malleus is 

 straighter, the incus more voluminous, and the stapes thinner, proportionately, than in 

 animals. There is no bony nucleus in the stapedian muscle. The muscle of the malleus 

 is lodged in a distinct canal belonging to the Eustachian tube. 



The external ear is composed of only two cartilages : one, forming the base of the 

 concha, represents that cartilage in animals ; the other, belonging to the auditory canal, 

 resembles the annular cartilage in the Horse. The concha is very irregular in shape, and 

 stands at an angle of from 15 to 45 from the temporal bone ; it is convex superiorly, 

 and terminates inferiorly by a small lobe. On its anterior face it presents prominences 

 and depressions ; the former are four in number : the helix, a fold encircling the ear 

 behind and above ; the antihelix, a concentric prominence, almost parallel with the 

 preceding ; the tragus, a triangular, pointed process, covered with hair, situated in front 

 of the auditory canal (meatus) ; the antitragus, opposite the tragus, behind the canal, 

 and above the lobule. The depressions are : the concha, a wide cavity, limited by the 

 antihelix ; the scaphoid fossa (fossa innominata) situated above the latter ; and the fossa 

 triangularis comprised between the helix and antihelix. 



The pavilion of the ear is traversed by several muscular fasciculi, which can have no 

 influence on its movements. The concha has also extrinsic muscles the anterior auri- 

 cularis (attrahens aurem), auricularis superioris (attolens aurem), and the auricularis 

 posteriores (retrahens aurem). The action of these on the concha is very slight. 



