DISEASES OF THE EYE AND ITS APPENDAGES. 



By M. 11. Teiuibowek, D. V. S. 

 lUevised by Li-onard ]'.-:irson, K. S., V. M. D.J 



DESCRIPTION. 



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

 the eye it becomes necessary to review tlie anatomy of tliis important 

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

 described, then its receptacle or orbital cavity, the muscles that move 

 it, the protective membranes, or eyelids, the membrana nictitans, or 

 accessory eyelids, and, lastly, the lachrymal api^aratus. 



The globe or ball of the eye is almost spherical in form. On 

 closer insi>ection, however, it appears 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 fi'ont of the ball with a greater con- 

 vexity than the i)osterior j)ortion. 



The eyeball consists of concentrically arranged coats and of re- 

 fracting media inclosed in them. The coats are three in number, 

 namely, (1) an extei-nal i^rotective 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, 

 opacjue part of the outer tunic, of which it forms about the jiosterior 

 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 smallei- sphere. It is dis- 

 tinguished from the sclerotic by being colorh'ss and transparent. The 

 choroid coat 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 bv a thickened 

 edge — the ciliary jn-ocesses. At the line of junction of the sclerotic 

 and cornea the iris passes ai'ross the interior of the eye. This (which 

 may l.)e viewed as a dependency of the choroid) is a muscular curtain 

 peiforated by an apeture termed the pupil. The retina will be 

 ]-ecognized as a delicate, glassy layer, lining the greater part of the 

 choi'oid. 

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