CUTTING THE ' HAW.' 263 



ever, is it with another structure connected with 

 the eye. 



In common with many mammals, with birds, 

 frogs, and several other vertebrates, the horse is 

 furnished with a sort of third eyelid, or ' nictitating 

 membrane,' as it is scientifically termed. In the 

 horse and dog it goes by the popular name of the 

 ' haw.' Without closing the external eyelid, the 

 animal can draw the nictitating membrane over the 

 eye, so as to sweep off any dust or extraneous sub- 

 stance that might injure the eye. This movement 

 may be seen to perfection in the owl tribe. 



It sometimes happens that this membrane becomes 

 inflamed, mostly, I believe, from the ammoniacal 

 vapour of ill- ventilated stables, and then it is apt 

 to protrude from the corner of the eye. The groom, 

 who naturally dislikes the red, unsightly projection, 

 never thinks of treating it as a case of subduable 

 inflammation, but cuts it off. From that time, the 

 membrane can never do its work rightly, and the 

 consequence too often is a partial or entire blinding 

 of the eye. 



