Eyelid

“ In the inner upper corner of the eye there is a minute tag--but larger in some races than in others--which is the last dwindling relic of the third eyelid, used in cleaning the front of the eye, which most mammals possess in a large and well-developed form. It can be easily seen, for instance, in ox and rabbit. In man and in monkeys it has become a useless vestige, and the dwindling must be associated with the fact that the upper eyelid is much more mobile in man and monkeys than in the other mammals. ”

“ When the eversion is greater, he directs us to perform an operation upon the inner part of the eyelid, making two incisions, which unite below like the Greek letter Λ, and afterwards dissecting out this lambdoid or triangular piece, and along with it the flesh below, which, he remarks, is not cartilaginous like the upper eyelid, but taking care to preserve the skin untouched. ”

“ The Eyelids. Palpebræ.—The eyelids are two thin folds which protect the eye. Externally they are covered with hair; internally by the thin membranous conjunctiva. The eyelids contain the Meibomian or tarsal glands, arranged in short rows passing perpendicularly inward from the edge of the lids; these may sometimes be seen with the naked eye as [410] broad yellowish lines. They secrete a substance which prevents the adhesion of the edges of the two lids. On the edge of each eyelid, three to four millimeters from the medial angle of the eye, is one of the openings of the lachrymal canals. ”

“ EYE-LASHES The eyelids are made of layers of muscle and cartilage with an outer surface of skin and an inner surface which is a continuation of the conjunctiva that covers the eyeball. In the edge of the eyelid a series of tiny glands are embedded. ”

“ In cases in which it is desirable to examine the inner side of the eyelid further than is possible by the above means, the upper lid may be drawn down by the eyelashes with the one hand and then everted over the tip of the forefinger of the other hand, or over a probe laid flat against the middle of the lid. When the interior of the eye must be examined it is useless to make the attempt in the open sunshine or under a clear sky. ”

“ What fungus produces an inflammation of the skin in cattle? Give the treatment.
CHAPTER XII DISEASES OF THE EYE GENERAL DISCUSSION.—The eye is situated in the orbital cavity, to which it is attached by muscles that rotate it in different directions. The orbit is lined by fibro-fatty tissues that form a cushion for the eye. Anteriorly it is protected by the eyelids, and in birds by a third eyelid that corresponds to the membrana nictitans of quadrupeds. The lachrymal gland which secretes the tears keeps the above parts moist.
The eye is the essential organ of vision. ”

“ The eyelids short and small, are thought wise and secret, yet covetous of great matters.
When the eyelids are long, and long hair on the eye-lashes, they signify a person of low sagacity, and false in his dealings. ”

“ But while we use the upper one to close our eyes, most birds use the lower one. They have also a third eyelid, inside the others, a thin, white sort of skin, that moves across the eye from side to side, and is called the "nictitating membrane." ”

“ Because the eyelashes assist to modify the light, and to protect the eye, without actually closing the eye-ids. When the eyelids are partially closed, as in very sunny or dusty weather, the eyelashes cross each other, forming a kind of shady lattice-work, from the interspaces of which the eye looks out with advantage, and sees sufficiently for the guidance of the body. ”

“ It is tied over the eyes like a pair of spectacles, being adapted to the forehead and nose, and hollowed out to favour the motion of the eyelids. A few rays of light only are admitted through a narrow slit an inch long, cut opposite to each eye. ”

“ Our flesh shrinks from what it dreads and responds to the stimulus of what it desires by a purely reflex action of the nervous system. Our eyelid closes before we are aware that the fly is about to enter our eye. ”

“ Observe further, how the eye, being naturally a tender organ, is supplied with eyelids as a house with a door, which may be opened to receive pleasant guests, and closed when danger approaches; the eye-lashes also manifestly serve as a sort of sieve to prevent the passage of any injurious particles which the wind might drive against the pupil, while the eyebrows form a sort of coping or fence which prevents the sweat from the forehead flowing into the organ of vision. ”

“ Our next care is the insertion of the eyes, which must be done while the eyelids are yet fresh. Some dexterity and skill are required in this operation, and on it will depend most of the beauty and character of the head. The seats of the eyes are supplied with a little cement, the eyes put in their place, and the eyelids properly drawn over the eyeballs: but if rage or fear are to be expressed, a considerable portion of the eyeballs must be exposed. ”

“ The eyelids form the shutters of the eye, defending it when waking, by closing upon its surface whenever danger is apprehended, moistening its surface when it becomes dry, and covering it securely during the hours of sleep. ”

“ The eyelashes, therefore, are like so many sentries, constantly moving to and fro, protecting a most important organ from injury. The eyelids are the shutters by which the windows are opened and closed. But they also cleanse the eye, keeping it bright and moist. ”

“ The eyes are, in the nodular form, almost always affected; nodules are frequently present in the eyelids, the upper as well as the lower, and are usually situated close to their margin. The earliest affection of the eye itself, which we have observed, is a faint clouding of the upper part of the cornea, which often appears as a very fine dotting of the corneal surface, only noticeable when one can compare the upper part of the cornea with the black pupil, and often requiring for its recognition the use of a lens. ”

“ Nervous movements of the eyelids may also be noted, either by ordinary inspection, or by lightly touching the lid of one eye while the other regards an object either at the near point or the distance. The visual axes are never parallel, and the deviation from the normal may become so marked as to constitute the condition of squint. ”

“ The eyes are very small; they are situated more upon the upper part of the head than is usual, and are directly behind the loose edge of the cuticular flap belonging to the bill. The eyelids are circular orifices concealed in the hair, and, in the male, are with difficulty discovered; but in the female there is a tuft of lighter hair, which marks their situation. ”

“ The eyes have small and oblique apertures like the Chinese, and from frequent attacks of ophthalmia and the effect of lamp smoke in their winter habitations adults of both sexes are disfigured by excoriated or ulcerated eyelids. The sight of these people is, from its constant exercise, extremely keen, and the habit of bringing the eyelids nearly together when looking at distant objects has in all the grown males produced a striking cluster of furrows radiating from the outer corners of each eye over the temples. ”

“ One or both eyes may appear small because of internal pain and retraction within their sockets, or from actual atrophy or contraction of the eyeball, the result of deep seated disease, or the organ may be congenitally small, and deep seated in the orbit, and the thick tardy eyelids may have a narrow opening through which they can only be partially seen. ”

“ And it is plain that such is the nature of the eyelids, for if the head is affected by never so little heaviness through sleepiness or drunkenness or anything else of the kind, we cannot raise the eyelids though their own weight is so small. ”

“ The eyelids are often rather carefully modeled and sometimes an eyeball is put in between the lids. These and perforated eyes seem to be the latest characters to be developed in the archaic art and it is significant that they are not found over such a wide area as the first five types of eyes given above. ”

“ Taking, however, “the more certain characters,” the “head with a convex, moderately capacious cranium, short, obtuse muzzle, gape not extending further than to beneath the eye, which (the eye) is rather small, round, filling closely the palpebral aperture” (that is, the eyelids fit closely25) ; “colour and surface as stated ”

“ In extreme cases the eyes protrude from their sockets to such a degree that the eyelids cannot be closed, and injury may thus arise to the constantly exposed eyeballs. Apart from such risk, however, the vision is rarely affected. ”

“ In September, when I first saw him, his left eye was very much diminished in size, and the cornea studded with white spots; the vision very imperfect, and constantly discharging water. The right eye was so opaque that neither iris nor pupil was to be seen, and he could only see the shadow of an object. ”

“ In other words, the contraction of the pupil in the excised eye of fishes and amphibia does not depend on an intraocular reflex involving the retina, but on the direct influence of light on one or more of the elements of the inner or pupillary part of the iris. It had been suggested that the phenomenon was due to the action of light on the endings of the nerve fibers in the sphincter muscle of the iris. ”

“ The modifications of the organs of sight do not so much affect the eyeball as the accessory apparatus. To an animal whose surface is always bathed with fluid, the complex arrangement which mammals generally possess for keeping the surface of the transparent cornea moist and protected, the movable lids, the nictitating membrane, the lachrymal gland, and the arrangements for collecting and removing the superfluous tears when they have served their function can not be needed, and hence we find these parts in a most rudimentary condition or altogether absent. ”

“ The iris is the part which gives the eye its colour; it is composed of a number of fibres, the outer ones radiating towards the centre, the inner ones forming a ring round the pupil; and behind these fibres is a coat of dark pigment or colouring matter, blue in some people, grey, brown, or black in others. When the light is very strong, and would pain the nerves inside if too much entered the pupil or window of the eye, then the ring of the iris contracts so as partly to close the opening. ”

“ The ocular buds appear towards the end of larval life as a simple mass of hypodermic cells, and form a compact layer on the dorsolateral face of the prothoracic segment, and clothe the cephalic ganglion or brain like a skull-cap. The central portion only is destined to form the eye, while the peripheral pad, continuing to thicken, gives rise to a voluminous and rounded mass, which meets on the median line that of the opposite side, and forms the integument of all the posterior part of the head. ”

“ But manufactured eyes are much preferable. I have frequently bought cases of white glass eyes and painted them at the back the right colour. While on the subject of eyes, it may be mentioned that carnivorous animals have the light in the eye down the eye from top to bottom, while granivorous animals have it across.
Next take the skin out of the solution and smear the inside well with a paste of arsenical soap. Put some wool into the ears, and draw the skin over the skull like a glove. ”

“ The compound eye is so delicate and wonderful, that great knowledge of anatomy or the science of optics is necessary before it can be really appreciated. Briefly, it is made up of a cluster of simple eyes, in each of which there are several parts. Beginning at the surface we have what is known as the facet, or cornea, which roughly corresponds to the surface of our own eyes. ”

“ Operation.—A double-edged needle is introduced through the cornea near its margin; on arriving at the place where the pupil ought to be, one edge is drawn against the iris, and divides it transversely, if possible, without injuring the lens; the fibres of the iris start back, contract, so that a sufficiently large central pupil may be obtained.{169}
2. Excision.—In the far more frequent cases in which there exist adhesions between iris and cornea, or iris and anterior capsule, incision is not sufficient, and it is necessary to excise a portion of the iris. ”

“ Unnatural impressions are made on the retina; flashes of strong light, or luminous sparks, appear to dart across the eyes; darkened spots are seen where none exist; gnats, flies, or other minute bodies, various in colour and brilliancy, seem to flutter before the face; or a single dark speck intercepts the vision. Usually the pupil is dilated and the iris insensible to the stimulus of light ”

“ That a change in the germ, which influences the formation of the retina, may affect at the same time also the formation of the cornea, the iris, the lens, the visual centres, etc., I admit, if necessary, although they are formations that differ much more from one another in their original nature than do probably hair and teeth. ”

“ In most cases of eccentric fixation, on the contrary, the eye quickly tires, and its appearance, with that of the face, is expressive of effort or strain. The ophthalmoscope1 reveals that the eyeball moves at irregular intervals, from side to side, vertically or in other directions. ”