THE SPECIAL SENSES. 201 



found in the neighborhood of hairs. These glands supply 

 a thick, oily material which greases the edges of the lids 

 and prevents their adhering together, and likewise prevents 

 the overflow of the tears upon the cheek. 



56. The Lachrymal Fluid, or the Tears. Just 

 within the outer part of the bony arch cf the brow, where 

 the bone may be felt to be sharper than in other positions, 

 is lodged a little organ called the lachrymal gland, the sit- 

 uation of which is indicated in Fig. 47, 1. This is the 

 gland whence flows the watery secretion, commonly called 

 the tears, which is designed to perform an exceedingly im- 

 portant duty in lubricating the lids, and in keeping the 

 exposed surface of the eyeball moist and transparent. For, 

 without this or some similar liquid, the front of the eye 

 would speedily become dry and lustreless, like that of a 

 fish which has been removed from the water : the simple 

 exposure of the eye to the air would then suffice to destroy 

 vision. 



57. This secretion of the tears takes place at all times, 

 during the night as well as the day; but it is seldom 

 noticed, except when under the influence of some strong 

 mental emotion, whether of sorrow or happiness, it is 

 poured forth in excess, so as to overflow the lids. Strong 

 light or a rapid breeze will, among many other causes, ex- 

 cite the flow of the tears. That portion of this secretion 

 which is not used in moistening the eye is carried off 

 into the nose by a canal situated near the inner angle of 

 the eye, called the nasal duct. This duct is shown in Fig. 

 47, 2, and is connected with each lid by delicate tubes, 

 which are indicated by dotted lines in the figure ; the as- 

 terisk marks the little opening in the lower lid, by which 

 the tears enter the nasal duct. By gently turning the 

 inner part of that lid downward, and looking in a mirror, 



56. The location of the lachrymal gland ? The use of the gland ? 



57. When does the secretion of the tears occur? The secretion not used for 

 the eye? Location of the nasal duct? Its use? The overflow of tears in old 

 people ? 



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