THE EYE AND ITS VISUAL STRUCTURE. 205 



inner angle of the eye, be carried down the duct, which 

 would irritate and obstruct it. No sooner do any of these 

 annoyances enter the eye but they are carried oflf by the 

 haw, which lies concealed within the inner corner of the 

 eye. This haw is a black or pied cartilaginous substance 

 of a triangular form, concave within and made exactly 

 to suit the globe of the eye ; while it is convex externally, 

 accurately fitting the membrane lining the lid, while the 

 base of it is reduced to a thin or almost sharp edge. The 

 horse has the voluntary power of suddenly protruding this 

 from its concealment, and passing it rapidly over the eye- 

 ball, clears ofi" every nuisance mixed with the tears, and 

 then being quickly drawn back, the dust or insect is 

 wiped off as the cartilage again passes under the corner of 

 the eye. 



In treating of disease of the haw, page 44, we mentioned 

 the barbarous practice of cutting out this valuable appen- 

 dage to the eye. This member is destined by nature as 

 a substitute for the want of hands for wiping the eye and 

 cleansing it from offensive matter. This being removed, 

 subjects the poor animal to pain in its eye for life, and 

 lays it open to the constant chance of inflammation from 

 dust or small pieces of gravel being blown into it. The 

 pain they thus inflict on the horse may be easily conceived 

 by any one having dust or other extraneous matter lodged 

 between the eyelid and eye, and being without hands to 

 wipe it out. 



THE EYE AND ITS VISUAL STEUCTURE. 

 PLATE X. Fig. 8. 



The eye is of a spherical figure, yet not perfectly globular ; 

 or it may rather be considered as composed of the parts of 



