THE SENS )RIA^, FUNCTION. 7 



Kltrotica. A- It is an exceedingly strong membrane, composed of fibres inte wea ing 

 with each other, and almost defying the possibility of separation. An organ so 

 delicate and so important as the eye requires secure protection. 



It is a highly elastic membrane. It is necessary that it should be so, v 7 hen it is 

 considered that the eye is surrounded by several and very powerful muscles, which 

 must temporarily, and even for the purposes of vision, alter its form. The elasticity 

 of the sclerctica is usefully exhibited by its 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 participates in general disturbance or disorganisation, are rarely 

 Drought 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 sure symptom of wickedness. The 

 cornea fills up the vacuity which is left by the sclerotica in the fore part of the eye, 

 and, although closely united to the sclerotica, may be separated from it, and will 

 drop out like a watch-glass. It is not round, but wider from side to side than from 

 top to the bottom ; and the curve rather broader towards the inner than the outer 

 corner of the eye, so that the near eye may be Irnown from the off one after it is taken 

 from 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 rays of light may be rendered too convergent, and the vision indis- 

 tinct ; 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 sud- 

 denly 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 different plates, 

 laid over one another ; and between each, at least in a state of health, is a fluid that 

 is the cause of its transparency, and the evaporation of which, after death, produces 

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

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



There is nothing that deserves attention from the purchaser of a horse more than 

 the perfect transparency of the cornea over the whole of its surface. The eye should 

 be examined for this purpose, both in front, and with the face of the examiner close 

 to the cheek of the horse, under and behind the eye. The latter method of looking 

 through the cornea is the most satisfactory, so far as the transparency of that part of 

 the eye is concerned. During this examination the horse should not be in the open 

 air, but in the stable standing in the doorway and a little within the door. If any 

 small, faint, whitish lines appear to cross the cornea, or spread over any part of it, 

 they are assuredly the remains of previous inflammation ; or, although the centre and 

 bulk of the cornea should be perfectly clear, yet if around the edge of it. where it 

 unites with the sclerotica, there should be a 'narrow ring or circle of haziness, the 

 conclusion is equally true, but the inflammation occurred at a more distant period. 

 Whether however the inflammation has lately existed, or several weeks or months 

 have elapsed since it was subdued, it is too likely to recur. 



There is one caution to be added. The cornea in its natural state is not only a 

 Beautiful transparent structure, but it reflects, even in proportion to its transparency, 

 many of the rays which fall upon it ; and if there is a white object immediately before 

 the eye, as a light waistcoat, or much display of a white neckcloth, the reflection may 

 puzzle an experienced observer, and has misled many a careless one. The coal 

 should be buttoned up, and the white cravat carefully concealed. 



Within the sclerotica, and connected with it by innumerable minute fibies and 

 vessels, is the chornid coat, I. It is a very delicate membrane, and extends over the 

 whole of the internal part of the eye, from the optic nerve to the cornea. It secretes 

 a dark-coloured substance or paint, by which it is covered ; the intention of w hicli, 

 ik the inside of our telescopes and microscopes, is probably to absorl' ary \vand* r - 



