A complete handbook for the sanitary troops of the U S army and navy . THE NERVOUS SYSTEM AND SPECIAL SENSES 59 tcnial ear, the auditory canal, the tympanum or drum membrane,the middle ear, stretchinj, across which are the small bones orossicles, and the internal ear. The tym])anum is stretched likea drum-head across the auditory canal, separating the external andmiddle ears; in order that the air pressure on the two sides of thedrum may he equalized tiiere is an air tube leading from the middleear to the throat and known as the Eustachian tube; stoppage of thistube in chronic inflammation of
A complete handbook for the sanitary troops of the U S army and navy . THE NERVOUS SYSTEM AND SPECIAL SENSES 59 tcnial ear, the auditory canal, the tympanum or drum membrane,the middle ear, stretchinj, across which are the small bones orossicles, and the internal ear. The tym])anum is stretched likea drum-head across the auditory canal, separating the external andmiddle ears; in order that the air pressure on the two sides of thedrum may he equalized tiiere is an air tube leading from the middleear to the throat and known as the Eustachian tube; stoppage of thistube in chronic inflammation of the throat is one of the causes —Section of the Eye. i, Conjunctiva; 2, cornea ; 3, 3, iris ; 4, pupil; 5. kns;6, retina; 7, optic nerve. The sense of sight consists in the perception of light, color, form,size, and distance; it is resident in the eye. The eye (Fig. 26) is situated in the orbit, the projecting upperborder of which, together with the quickly moving lids, give it pro-tection. It is covered in front by a thin vascular membrane whichalso lines-the lids and is known as the conjunctiva. .Light entersthrough the transparent cornea which is set in front of the eye likea watch-glass; behind the cornea is hung a curtain of muscular fibersvariously colored and called the iris; the black pupil is really a holein the iris to let in the light which then passes through a crystallinelens just behind the pupil and is brought to a focus on the retina; the 60 ANATOMY AND PHYSIOLOGY retina is merely an expansion of the optic nerve which transmits thehiminous impressions to the brain. The dense white outer coat
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfirstaidinillnessand
