DISEASES OF THE EYE AND ITS APPENDAGES. 



By M. R. Tbumbower, D. V. S. 

 [Revised in 1904 by Leonard rearf5on, B. S., V. M. D.] 



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 mem- 

 brana nictitans, or accessory eyelids, and, lastly, the lachrymal 

 apparatus. 



The glohe, or hall, of the eye approaches the spherical in form. On 

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

 bined 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, projects at the front of the ball with a greater con- 

 vexity 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 num- 

 ber, namely, (1) an external protective tunic made up of the sclerotic 

 and cornea; (2) a middle vascular and pigmentary tunic, the chxyi'md; 

 (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 men- 

 tioned. The cornea forms the remaining one-sixth of the outer tunic, 

 being coextensive with the segment of the smaller sphere. It is dis- 

 tinguished from the sclerotic by being colorless and transparent. 

 The choroid coat will be re<?ognized 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 be 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. 



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