THE TEAR APPARATUS. 319 



or two rows along each lid and helping to keep dust from 

 falling into the eye; and, when the lids are nearly closed, 

 to protect it from a dazzling light. 



The Lachrymal Apparatus consists of the tear-gland in 

 each orbit, of ducts which carry its secretion to the upper 

 eyelid, and of canals by which this, unless when excessive, 

 is carried off from the front of the eye without running 

 down over the face. The lachrymal or tear gland, about 

 the size of an almond, lies in the upper and outer corner of 

 the orbit. It is a compound racemose gland, from which 

 twelve or fourteen ducts run and open at the outer corner 

 of the upper eyelid on its inner surface. The secretion 

 there poured out is spread evenly over the exposed part of 

 the eye by the movements of winking, and keeps it moist ; 

 finally it is drained off by two lachrymal canals, one of 

 which opens by a small pore on an elevation, or papilla, 

 near the inner end of the margin of each eyelid. The aper- 

 ture of the lower canal can be readily seen by examin- 

 ing its papilla in front of a looking-glass. The canals 

 run inwards and open into the lachrymal sac, which lies 

 just outside the nose, in a hollow where the lachrymal and 

 superior maxillary bones (Land MX, Fig. 16) meet. From 

 this sac the nasal duct proceeds to open into the nose- 

 chamber below the inferior turbinate bone (q, Fig. 41, p. 

 133). 



Tears are constantly being secreted, but ordinarily in 

 such quantity as to be drained off into the nose, from 

 which they flow into the pharynx and are swallowed. 

 When the lachrymal duct is stopped up, however, their 



Of what parts does the lachrymal apparatus consist? Describe the 

 lachrymal gland. Where do its ducts open? How is the front of the 

 eyeball kept moist? Describe the arrangement by which the tears 

 are usually carried off. 



