THE EYE AND ITS VISUAL STRUCTURE 1 83 



duties which are attributed to the eyelashes, namely, 

 to obstruct the rays of light in those directions in 

 which it would come with the greatest force both 

 from above and below ; while at the same time the 

 field of view is quite open, so far as respects the 

 pasture on which the horse is grazing. 



0, 0. The ciliary, or hair-like processes. 



p. The vitreous, or glass-like humour, which fills the whole 

 of the cavity of the eye behind the lens. It is a clear 

 gelatinous fluid, resembling the white of an egg. It 

 fills about three-fourths of the globe of the eye, and 

 extends from the posterior part as far forward as the 

 ciliary ligament. 



g. The aqueous, or water-like humour which fills the space 

 between the cornea and the crystalline lens. 



It is by means of this humour that the cornea is 

 preserved in its rounded form. A small portion of 

 it is behind the iris. 



r. The retina, or fine net-like expansion of the optic-nerve, 

 which is spread over the whole of the choroides, as far 

 as the lens. 



s. The optic-nerve, or nerve of sight. 



/. The conjunctiva, or that membrane which covers the fore 

 part of the eye, and which lines the lids, and even 

 extends to the transparent portion of it. It is trans- 

 parent, and transmits colour to the parts beneath. It 

 is very liable to inflammation, during which the 

 vessels of the lining of the lids will become engorged 

 with blood, and present an intensely red appearance, 

 which extends itself to those vessels in the white of 

 the eye, which will also become completely congested 

 with blood, and will ultimately render the cornea 

 clouded and opaque. 



A defect of sight in the horse is more dangerous 

 than total blindness, for this reason, that one with 

 a defect of sight will start and shy at every object 



