Buckmaster's Elements of animal physiology / by John Angell.

  • Angell, John
Date:
1866
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Licence: Public Domain Mark

Credit: Buckmaster's Elements of animal physiology / by John Angell. Source: Wellcome Collection.

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    vestibule forms the rudwientary part of the ear, being found in all animals who possess special organs of hearing. The vibratory particles, or sou?id waves of the atmosphere, enter the external or auditory canal, strike against and put the membrana tympani into vibration; it puts the chain of ossicles of the middle ear into vibration; they transmit their motion to the membrane of the fenestra ovalis, which communicates it to the fluid contained in the labyrinth; the fluid transmits it to the network of the auditory nerve, which is spread over the walls of the me7nbranous labyrinth and the lamina spiralis of the cochlea; and the nerve conveys the impression to the brain (the sensorium), where it develops the sensation of sound. The sensation of hearing sometimes originates in the brain itself without the intervention of the organs of hearing ; it is then termed subjective. The Auditory, or soft portion of the 7th cranial nerve, is distributed to the inside of the membranous labyrinth (more especially to the saccule and the utricle), and to the lamina spiralis of the cochlea. The Sense of Sight, by means of which we are brought into relation with the external world through the medium of light, is seated in the eyes. The Eyes are organic optical instruments, by which the light is collected, brought to a focus, and thrown on to a nervous screen, on which it produces an inverted image of objects placed before it, as in the case of an ordinary magic lantern. It is supplied with certain mechanical fittings and appendages— muscular, tendinous, and glafidular,—by which it is moved, cleaned, and adjusted with great accuracy. (See Fig. 83.) Sight does not take place in the eye, but in the brain. Structure of the Eye.—The eye comprises the Y