Chap, hi.] SIGHT. 979 



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 parakyzed 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 on- 

 wards out of the canals, which, upon the relaxation of the 

 orbicularis, dilate and receive a fresh quantity. Others main- 

 tain that a special arrangement 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. 



