164 



AMERICAN FARMER'S HORSE BOOK. 



#. 



CHAPTER yi. 



DISEASES OF THE EYE. 

 I 



The above is a sectional view of the eye, exhibiting its 

 different parts. It also shows in what manner the sensation 

 of sight is produced. 



A B a supposed object viewed by the animal, and an inverted image of which, 



a, 6, is thrown on the retina at the back of the eye. 

 c c The points where the rays, having passed the cornea and lens, converge 



by the refractive power of the lens. 

 d e The rays proceeding from the extremities of the object to the eye. 

 / The cornea, or horny and transparent part of the eye, covered by the con- 



junctiva^ Uniting different parts together. 

 gr The crystalline (crystal or glassy) lens, behind the pupil, and in front of 



the vitreous humor. 

 h h Muscles of the eye. 



i The optic nerve, or nerve of sight. 



k The sclerotiva (hard, firm coat) covering the whole of the eye, except the 



portion occupied by the cornea, and being a seeming prolongation of 



the covering of the optic nerve. 

 I The choToides (receptacle, or covering), or choroid coat, covered with a 



black secretion, or paint. 

 m m The im, or rainbow-colored circular membrane under the cornea, in front 



of the eye, and on which the color of the eye depends. The dupli- 



cature behind is the uvea, so called from being colored like a grape. 



The opening in the center is the pupil. 

 n n The ciliary (hair-like) processes, which are folds, or plaits, of the choroid coat, 



reflected from the side of the eye to the edge of the crystalline lens. 



