552 THE SENSORIAL FUNCTION 



The soiled colled ad by the outer ear, passes through the lower or annular /ing 

 shaped, cartilage, and through irregularities which, while they break and modify .t, 

 Bonvey it on to another canal, partly cartilaginous and partly bony, conducting 

 immediately to the internal mechanism of the ear. This canal or passage, is called 

 the external auditory passage, and -it the base of it is placed, stretching acioss it, and 

 closing it, a thick arid elastic meml rane, membrana tympani, called the membrane of 

 the drum. This membrane is supplied with numerous fibres, from the fifth pair, 01 

 sensitive nerve of the head, for it is necessary that it should possess extreme sensi 

 bility. 



Between this membrane and a smaller one almost opposite, leading to the still 

 interior part of the ear, and on which the nerve of hearing is expanded, are four little 

 bones, united to these membranes, and to each other. Their office is to convey, 

 more perfectly than it could be done through the mere air of the cavity, the vibrations 

 that have reached the membrana tympani. 



These bones are highly elastic ; and covered by a cartilaginous substance, elastic 

 also in the greatest degree, by means of which the force of the vibration is much 

 increased. 



It is conveyed to a strangely irregular cavity, filled with an aqueous fluid, and the 

 substance or pulp of the portio mollts or soft portion of the seventh pair of nerves, the 

 auditory nerve, expands on the membrane that lines the walls of this cavity. 



Sound is propagated far more intensely through water than through air; and there- 

 fore it is that an aqueous fluid occupies those chambers of the ear on the walls of 

 which the auditory nerve is expanded. By this contrivance, and by others, which 

 we have not space now to narrate, the sense of hearing is fully equal to every possible 

 want of the animal. 



The Eye is a most important organ, and comes next under consideration, as inclosed 

 in the bones of the skull. The eye of the horse should be large, somewhat but not 

 too prominent, and the eyelid fine and thin. If the eye is sunk in the head, and 

 apparently little for there is actually a very trifling difference in the size of the eye 

 in animals of the same species and bulk, and that seeming difference arises from the 

 lurger or smaller opening between the lids and the lid is thick, and especially if 

 there is any puckering towards the inner corner of the lids, that eye either is diseased, 

 or has lately been subject to inflammation ; and, particularly, if one eye is smaller 

 than the other, it has a', no great distance of time, been inflamed. 



The eye of the horse enables us with tolerable accuracy to guess at his temper. 

 If much of the white is seen, the buyer should pause ere he completes his bargain ; 

 because, although it may, yet very rarely, happen that the cornea or transparent part 

 is unnaturally small, and therefore an unusual portion of the white of the eye is seen, 

 experience has shown that this display of white is dangerous. The mischievous 

 horse is slyly on the look out for opportunities to do mischief, and the frequent back- 

 ward direction of the eye, when the white is most perceptible, is only to give surer 

 effect to the blow which he is about to aim. 



A cursory description of the eye, and the uses of its different parts, must be given. 



The eyes are placed at the side of the head, but the direction of the conoid cavity 

 which they occupy, and of the sheath by which they are surrounded within the orbit, 

 gives them a prevailing direction forwards, so that the animal has a very extended 

 field of vision. We must not assert that the eye of the horse commands a whole 

 sphere of vision ; but it cannot be denied that his eyes are placed more forward than 

 those of cattle, sheep, or swine. He requires an extensive field of vision to warn hin? 

 of the approach of his enemies in his wild state, and a direction of the orbits con- 

 siderably forward, in order to enable him to pursue with safety the headlong course 

 to which we sometimes urge him. 



The eyo-ball is placed in the anterior and most capacious part of the orbit, nearei 

 lo the f-ontal than the temporal side, with a degree of prominence varying with 

 different individuals, and the will of the animal. It is protected by a bony socket 

 '.lenea'h anil on the inside, but is partially exposed on the roof and on the outside. Il 

 .8, however, covered and secured by thick and powerful muscles by a mass of 

 dirrse matter w>>ich is distributed to various parts of the orbit, upon which the oyf 



