242 ANATOMY FOE NUBSES. [CHAP. XIX. 



the lachrymal sac, which is the upper dilated portion of the 

 nasal duct. 



The nasal duct is a membranous canal, about three-quarters 

 of an inch (19 mm.) in length, which extends from the lach- 

 rymal sac to the inferior meatus of the nose, into which it opens 

 by a slightly expanded orifice. 



The tears consist of water containing a little salt and albu- 

 min. They are ordinarily carried away as fast as formed, but 

 under certain circumstances, as when the conjunctiva is irri- 

 tated, or when painful emotions arise in the mind, the secretion 

 of the lachrymal gland exceeds the drainage power of the nasal 

 duct, and the fluid, accumulating between the lids, at length 

 overflows, and runs down the cheeks. 



