THE EYE 359 



growing together. The cilia, or eyelashes, act as shades to the 

 eye and as feelers to warn of danger in the dark. The conjunctiva 

 has already been described. Being highly sensitive it warns us 

 of the danger of permitting particles to remain in contact with 

 the eye. 



The Lachrymal Apparatus. This is an additional means of 

 protection to the eye, and consists of the lachrymal gland, with 

 excretory ducts, the lachrymal canals, the lachrymal sac, and 

 nasal duct. The lachrymal gland is located in the upper, outer 

 part of the orbit, and pours its secretion through several ducts upon 

 the eyeball. The constant winking keeps it distributed over the 

 eye. It is prevented from flowing off upon the face, unless in 

 excessive quantity, by the oil from the Meibomian glands. The 

 orifices of the two lachrymal canals open at the inner corner of the 

 eye and receive the fluid. They empty it into the lachrymal sac, 

 and this discharges it into the nasal duct which opens in the nasal 

 cavity. Here it evaporates as fast as discharged. When the se- 

 cretion is excessive it flows over the lids down the face in the form 

 of tears. The tears consist mostly of water containing salts in solu- 

 tion, common salt, or chloride of sodium, being most abundant. 

 The use of the lachrymal fluid is obvious. It maintains the clear- 

 ness of trie eye by keeping it moist, and washes dust and foreign 

 particles away and protects the delicate mucous membrane from 

 the irritating effect of the air. 



Experiment. Secure from the butcher the eyes from an ox, pig, or sheep. If 

 possible get several specimens to use in case one is spoiled in dissection, and also 

 that you may try different methods of preparing them for illustration. Place in 

 water until ready for use. With the aid of Fig. 243 examine each part of the eye. 



Notice that the crystalline lens if placed over print will magnify the words. 



Position of the Eyes. Animals are divided into two classes as 

 to the position of their eyes. 



1. All hunted animals have side eyes, or, in other words, their 

 eyes are placed on the sides of the heads, which enables them to 

 look in opposite directions for approaching danger. 



2. Hunting animals have front eyes, since such animals hunting 

 for food must have eyes for looking directly ahead, 



