13 



when the orbicular muscle ceases to contract; thus the eye 

 is opened. 



On the outer part of the free border of the upper lid are 

 large eye lashes — but the lashes of the lower lid are fewer 

 in number and smaller. On the inner part of the free border 

 of each lid are little oil glands which lubricate the free mar- 

 gins of the lids and keep them from growing together or 

 adhering to one another during sleep. 



The membrana nictitans, third eyelid, the "haw," or the 

 eye washer," is placed at the inner angle of the eye; its 

 framework is a fibro-cartilage, elastic and irregular in shape, 

 thick at its back part, and thin at its anterior or free part, 

 which is covered by the conjunctiva. This lid is continued 

 behind by a strong, fatty cushion, which insinuates itself 

 between all the muscles of the eye. This lid is moved over 

 the anterior surface of the eyeball to remove dust particles, 

 small seeds, etc. It has no special muscle, but is pushed 

 over the eye when the eyeball is drawn backward into the 

 orbital cavity or socket by the posterior muscle of the eye. 

 When this lid is continually drawn, or pushed out, over 

 the eye, as in tetanus, lock jaw, etc., some persons say the 

 horse is affected with the "hooks;" and occasionally the bar- 

 barous treatment of cutting off these protecting and useful 

 lids is practiced. It would be about as sensible to cut off 

 the hands of a man to keep him from rubbing his eye 

 when it becomes irritated by dust, etc. 



The Lachrymal Apparatus comprises the gland which 

 secretes the tears and the canals which carrv the extra tear 

 fluid to the external openings of the nasal cavity. The 

 lachrymal or tear gland is situated above the eyeball and 

 below the rim of the orbit ; it secretes the tear fluid which is 

 carried to the surface of the eye by little ducts or canals that 

 open in the inner surface of the eyelids. The tears are 

 spread over the eye by the movement of the lids called 

 winking. At the inner or nasal angle of the eye is a little 



