THE SE^SORIAL FUXCTIOX. 161 



The co7ij'imctu-a, f, is that membrane wMcli lines tlie lids, and covers 

 tlie fore part of the eye. It spreads over all that we can see or feel of the 

 eye, even its transparent part, and is then reflected over the internal 

 surface of the lid. It is itself transparent, and ti-ansmits the colour of the 

 parts beneath. It is veiy susceptible of inflammation, during which the 

 lining of the lids will become intensely red, and the white of the eye will 

 be first streaked Avith I'ed vessels, and then covered with a complete mesh 

 of them, and the cornea will become cloudy and opaque. It is the seat of 

 various diseases, and, particularly, it first announces that sad inflammation 

 of the horse's eye, which bids defiance to the veterinary surgeon's skill 

 and almost invariably terminates in blindness. 



The examination of the conjunctiva, by turning down the lid, will en- 

 able us to form an accurate judgment of the degree of inflammation which 

 exists in the eye. 



Covering the back part of the eye, and indeed four-fifths of the globe 

 of it, is the sclerotica, h. It is an exceedingly strong membrane, composed 

 of fibres interweaving Avith each other, and almost defying the possibiHty 

 of separation. An organ so delicate and so important as the eye, requires 

 secure protection. 



It is to a certain extent comparatively inelastic. It is necessary that it 

 should be so, when it is considered that the eye is surrounded by several 

 very powerful muscles, which must temporarily, and even for the purposes 

 of vision, alter its form. The slight elasticity of the sclerotica is usefully 

 developed in causing the globe of the eye to resume its former and natural 

 shape, as soon as the action of the muscle ceases. 



The sclerotica has very few blood vessels — is scarcely sensible — and its 

 diseases, except when it jjarticipates in general disturbance or disorganisa- 

 tion, are rarely brought under our notice. 



The cornea is, or we should wish it to be, the only visible part of the 

 horse's eye, for the exhibition of much white around it is a frequent 

 symptom of wickedness. The cornea fills up the vacuity which is left by 

 the sclerotica in the fore part of the eje, and, although closely united 

 to the sclerotica, may be separated from it, and will drop out hke a watch- 

 glass. It is not round, but wider from side to side than from the top to 

 the bottom ; and the curve rather broader towards the inner than the 

 outer comer of the eye, so that the near eye may be known frora the off" 

 one after it is taken froni the head. 



The convexity or projection of the cornea is a point of considerable 

 importance. The prominence of the eye certainly adds much to the 

 beauty of the animal, but we shall see presently, when we consider the eye 

 as the organ of sight, that by being too prominent, the i-ays of light may 

 be rendered too convergent, and the vision indistinct ; or, if the cornea is 

 small and flat, the rays may not be convergent enough, and perfect vision 

 destroyed. In either case the horse may unpleasantly start, or suddenly 

 and dangerously turn round. An eye neither too prominent nor too flat 

 will be nearest to perfection. 



It should be perfectly transparent. Any cloudiness or opacity is the 

 consequence of disease. It is an exceedingly firm and dense membrane, 

 and can scarcely be pierced by the sharpest instrument. The cornea is 

 composed of many diff'erent plates, laid over one another ; and between 

 each, at least in a state of health, is a fluid that is the cause of its trans- 

 parency, and the evaporation of which, after death, produces the leaden 

 or glazed appearance of the eye. Wlien it appears to be opaque, it is not 

 often, and never at first, that the cornea has imdergone any change. 



Within the sclerotica, and connected with it by innumerable minute 

 fibres and vessels, is the choroid coat, I. It is a very dehcate membrane, 



ii 



