DISEASES OF THE EYE AND ITS APPENDAGES. 



By M. R. TRUMBOWER, D. V. S., Sterling, 111. 



For the sake of gaining a clear comprehension of the diseases of the 

 eye it becomes necessary to review the anatomy of this important organ. 

 The essential organ of vision or globe of the eye will be first described, 

 then the receptacle of this globe or orbital cavity, the muscles that 

 move it, the protective membranes or eyelids, the membraua nictitaus 

 or accessory eyelids, and, lastly, the lachrymal apparatus. 



The globe or ball of the eye approaches the spherical inform. On 

 closer inspection, however, it will appear to be made up of two combined 

 portions from spheres of different sizes. The posterior portion, forming 

 about five-sixths of the ball, is a sphere of comparatively large size with 

 a small segment cut off it in front, and at this point there is applied to 

 it the anterior portion, which, being a segment of a smaller sphere, pro- 

 jects at the front of the ball with a greater convexity than the posterior 

 portion. 



The eyeball consists of concentrically arranged coats, and of refract- 

 ing media inclosed within these coats. The coats are three in number, 

 viz, (1) an external protective tunic made up of the sclerotic and cornea; 

 (2) a middle vascular and pigmentary tunic, the choroid; (3) an internal 

 nervous layer, the retina. The sclerotic is the white opaque part of the 

 outer tunic, of which it forms about the posterior five-sixths, being 

 coextensive with the larger sphere already mentioned. The cornea, 

 forms the remaining one sixth of the outer tunic, being coextensive 

 with the segment of the smaller sphere. It is distinguished from the 

 sclerotic by being colorless and transparent. The choriod eoat will be 

 recognized as the black layer lying subjacent to the sclerotic. It does 

 not line the cornea, but terminates behind the line of junction of that 

 coat with the sclerotic by a thickened edge the ciliary processes. At 

 the line of junction of the sclerotic and cornea, the iris passes across 

 the interior of the eye. This, which may l>e viewed as a dependency 

 of the choroid, is a muscular curtain perforated by an aperture termed 

 the pupil. The retina will be recognized as a delicate glassy layer, 

 lining the greater part of the choroid. 



The refracting media of the eye are three in number, viz, (1) the 



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