CHAP, in.] _ SIGHT. 1313 



The chief use of the act of blinking is to keep the surface of 

 the cornea moist, and so transparent ; if the cornea be kept un- 

 covered for a few minutes its dried surface soon becomes dim. But 

 besides this, blinking undoubtedly favours the passage of tears 

 through the lachrymal canaliculi into the lachrymal sac, and 

 hence when the orbicularis is paralysed tears do not pass so readily 

 as usual into the nose ; but the exact mechanism by which this is 

 effected has been much disputed. According to some authors, the 

 contraction of the orbicularis presses the fluid onwards out of the 

 canals, which, upon the relaxation of the orbicularis, dilate and 

 receive a fresh quantity. Others maintain that a special arrange- 

 ment of muscular fibres keeps the canals open even during the 

 closing of the lids, so that the pressure of the contraction of the 

 orbicularis is able to have full effect in driving the tears through 

 the canals. 



