THE STRUCTURE AND FUNCTIONS OF THE EYE. 251 



inflammation, or inflammatory fever, becomes very red. In 

 staggers, and some other disorders of the stomach, and organs 

 subservient to digestion, it becomes of a deep yellow or orange 

 colour. This membrane is closely united to nearly one half of 

 the sclerotic coat, or white of the eye, and has been thought to 

 be continued in a very attenuated and transparent state over the 

 cornea also. In injuries of the eye, this membrane becomes 

 red; but, in internal diseases, it should always be examined, as 

 redness in that case indicates general inflammatory action, and 

 points out the necessity of copious bleeding. In the inner 

 corner of the eye there is a small fleshy eminence, named 

 caruncle, which separates the two open extremities of the lachry- 

 mal ducts, named puncta lachrymalia, and thus allows the tears 

 to be forced into them by the contraction of the orbicular muscle. 

 In the human eye, the tears pass from the puncta lachrymalia 

 into a small bladder or sac, which does not exist in the horse ; 

 in him there is one continued membranous tube from the inner 

 corner of the eye to the lower part of the nostril. The termi- 

 nation of the lachrymal tube, or duct, in the horse, has often 

 been mistaken for an ulcer in horses suspected of glanders ; but 

 it does sometimes become ulcerated from the acrimony of the 

 tears, or from the strong preparations that are sometimes ap- 

 plied in diseases of the eye. I have seen this happen from the 

 application of powdered sal ammoniac (muriate of ammonia) to 

 the eye. Sometimes the termination, or orifice, of the lachrymal 

 duct becomes closed by inflammation, or the cicatrisation of an 

 ulcer, and then it bursts above, and the ruptured part becomes 

 an ulcer. According to Lafosse, the disease named fistula 

 lachrymalis takes place in the horse ; but of this I have seen 

 only one case. In glanders, however, there is often, indeed 

 generally, a slight purulent or mucous discharge from the inner 

 corner of the eye, which probably proceeds from the lachrymal 

 duct. The membrana nictitans, or haw, as it is commonly 

 named, is situated in the inner corner of the eye. That part 

 which comes over the eye is a thin slippery membrane, which, 

 towards its basis, becomes thicker, and cartilaginous. Its basis 

 is of some thickness, and imbedded in fat ; there are no muscles 

 attached to it ; but when the eye is drawn into the orbit, and 

 towards the inner corner, the basis of the haw is prevented from 

 following it by the bones of the orbit ; the thin membranous 

 part of the haw is thus forced over the eye, and serves to re- 

 move dust or flies that may have fallen upon the cornea. 



The eye is moved by seven muscles, which arise from within 

 the orbit, or socket, and terminate in thin sheets of tendon, 

 which, with the sclerotic coat and conjunctiva, form what is 

 called the white of the eye. Of these there are four straight 

 muscles rising from the bottom of the orbit, and inserted into 

 <hc outer coat of the eye. One of them is situated at the upper, 



