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Sclerotic, retina, choroid, vitreous humour, lens, aqueous humour, all are present.
There is reason that we should give careful attention to the views of Heerfordt and Zirm, that obstruction to the venous outflow may be the effective cause of the disease. Zirm believes the venous plexus of the choroid is an essential part of the mechanism for the regulation of intra-ocular tension, the necessary vaso-motor control depending on nerve centers situated in the iris. Nerve Control
Head of a chick embryo, four days old, from below. n nasal pit, o upper-jaw process of the first gill-arch, u lower-jaw process of same, k double apostrophe second gill-arch, sp choroid fissure of eye, s gullet. Heads of chick embryos: 2.309 from the end of the fourth, 2.310 from the beginning of the fifth week. There is little to be said of the development of the lower sense-organs.
In these cases the lesions have consisted of detachment of the retina, optic atrophy, cataract, hemorrhages into the retina, and rupture of the choroid, paralysis of the oculomotor muscles, and paralysis of the optic nerve. According to Buller of Montreal, such injuries may arise from the mechanic violence sustained by the patient rather than by the thermal or chemic action of the current.
The cornea, a clear, transparent, circular disk, fits into the sclerotic, somewhat as the crystal fits into the metallic case of a watch, forming a covering for its dial. It projects from the general contour of the eyeball, not unlike a rounded bay-window, and is often spoken of as the "window of the eye." Lining the inner surface of the sclerotic is the second coat, the choroid.
The choroid coat, which constitutes the second investing membrane of the eye, is of a dark brown color upon its outer surface, and of a deep black within.
This fibrous envelope takes the form of a closed round vesicle, surrounding the whole of the ball and pushing between the lens and the horny plate at its outer side. The round wall of the capsule soon divides into two different membranes by surface-cleavage. The inner membrane becomes the choroid or vascular coat, and in front the ciliary corona and iris.
Roll up a piece of blackened paper in the form of a tube, black surface innermost, and place the eye in it with the cornea directed forward. Look at an object e.g., a candle-flame and observe the inverted image of the flame shining through the retina and choroid, and notice how the image moves when the candle is moved. Experiment 175.
First, the choroid coat of the eye, on which the semitransparent retina is expanded, is of different colour in different animals; in those which feed on grass it is green; from hence there would appear some connexion between the colour of the choroid coat and of that constantly painted on the retina by the green grass.
The back of the iris is lined with dark pigment, and as the coloring matter is more or less abundant, we may have a variety of colors. This pigment layer and that of the choroid and retina absorb the light entering the eye, so that little is reflected. The pupil appears black, just as the open doorway to a dark closet seems black.
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