EXTERNAL STRUCTURE. 



ABA supposed object viewed by the animal, and an inverted image of which, «, b, is 

 thrown on the retina at the back of the e3'e. 



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

 refractive power of the lens. 



de 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 conjunctiva, miitinc 

 different parts together. 



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

 humour. 



hh Muscles of the eye. 



i The optic nerve, or nerve of sight. 



k The sclerotica (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. 



/ The choroides (receptacle or covering), or choroid coat, covered with a black secretion or 

 paint. 



m m The iris, or rainbow-colom-ed circular membrane, under the cornea, in front of the 

 eye, and on Avhich the colour of the eye depends. Tlie duphcature behind is thy 

 uvea, from being coloured like a grape. Tlie opening in the centre is the pupil. 



n n The ciliary (hair-like) processes. 



The retina, or net-like expansion of the optic nerve, spread over the whole of the cho- 

 roides as far as the lens. 



p The vitreous (glass-like) humour filling the whole of the cavity of the eye behind the lens. 



q The aqueous (water-like) humour filling the space between the cornea and the lens. 



The cojijiuictiva, f, is that membrane which lines the Hds, and covers the 

 fore part of the eye. It covers all that we can see or feel of the eye, and 

 even its transparent part. It is itself transparent, and transmits the colour 

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

 the lining of the Hds will become intensely red, and the white of'^the eye 

 will be first streaked with red 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 in it commences the sad in- 

 flammation of the horse's eye, which bids defiance to the veterinary sur- 

 geon's skill, and, almost invariably, terminates in blindness. 



The examination of the conjunctiva, by turning down the lid, will enable 

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

 in the eye. Horsemen and farriers, however, seem to think that it likewise 

 indicates the degree of inflammation in almost every other part, or, at least, 

 of the general fever which may accompany local inflammation. There is 

 apart which much more clearly hidicates this, and especially if the general 

 disturbance be accompanied or produced by any affection of the lungs— a 



