82 



THE MODERN SYSTEM 



has a double row in the centre, not extending 

 from canthus to cantlms ; these lids are seldom 

 diseased, or even the cause of disease. 



THE CONJUNCTIVA. 



The conjunctiva is immediately connected 

 with the eye-lids, the haw, and the orbit ; it 

 possesses three different structures, that is, 

 three separate degrees of vascularity. It lines 

 the inner surface of the eye-lids, covers the 

 eye-ball, being reflected over every part ; 

 now this membrane is highly vascular in that 

 part lining the eye-lids, it is less so over the 

 opaque cornia, and still less over the trans- 

 parent cornia, never admitting red particles 

 of blood, unless in a state of inflammation. 

 Now the eye-lids have a secretion of their own, 

 to protect them from the tears, whir-h, though 

 congenial to the eye, are not so to the edges 

 of the palpebrcB ; and it is a well known fact, 

 shewing the susceptibility of parts, for the 

 salt that is in the tears will at any time 

 inflame the cheek, but not the eye ; but warm 

 water applied to the eye, will inflame it, and 

 be congenial to, and relieve the cheeks ; 

 though we cannot account for these facts, but 

 by the different susceptibility of the nerves 

 going to these parts. 



THE FUNCTIONS OF THE LACHRA'MAL GLANDS, 

 TEARS, CONJUNCTIVA, EYE-LIDSj HAW, AND 

 RETRACTOR MUSCLE. 



As the above parts of the eye are all, more 

 or less, blended together, I have thought it 

 best to give their functions together, from the 

 intimate connection one has with the other. 

 The apparent use of the eye-lid, is to protect 

 the eye from foreign matter, and also to regu- 

 late the admission of light ; independent of 

 ihese, the inner surface of the upper eye-lids. 



covered by the conjunctiva, is connected with 

 the tears, which flow between the eye-ball 

 and eye-lid, the conjunctiva is thus prevented 

 from coming in contact by a fluid ; the eye-lids 

 also secret a fluid of their own, which pre- 

 vents any tendency to irritation ; the action of 

 the lachrymal glands is, at intervals, even in 

 sleep, taking place, though there may be but 

 little wanted ; but any foreign matter, even 

 the wind, will at once excite their action : this 

 is occasioned by the nerves of the eye-ball 

 being irritated, the tears, in consequence, are 

 thrown out to alleviate such irritation. Be- 

 tween these glands and the mind, there is also 

 great sympathy, and when their action is ex- 

 cited, so that the secretion be too extensive to 

 be carried off by the nose, the tears flow over 

 the cheeks, and constitutes weeping. This 

 secretion is also affected by the action of the 

 retractor muscle, which, acting with the ad 

 ductor muscle, the eye-ball is brought to the 

 inner canthus, and the haw forced over th© 

 eye-ball. Foreign matter very seldom occa- 

 sions blindness, for the tears and eye-bal? 

 moving in one direction, and the haw in & 

 contrary one, any foreign matter is quickly 

 dislodged. 



The tears, then, we see, keep the parts 

 moist, transparent, and, remove the waste 

 from evaporation, which is always going for- 

 ward in moist external surfaces. The tears 

 having performed their oflfice of lubricating the 

 eye-ball, and the parts attached, they pass on into 

 the ducts, called puncta lachrymalis, situated 

 at the inner canthus of the eye. This duct 

 in the Horse is but little larger than in the 

 human subject ; passing through a canai, 

 partly bony and partly membranous, termi- 

 nates at the lower end of the nostrils, much 

 increased in size. This formation in man is of 



