126 ZOOLOGY. 



angle of the eye ; by these the tears are conveyed to the 

 surface of the eyeball. Here they are spread over the surface 

 by the movements of the eyeball and eyelids, until they 

 collect towards the inner angle of the eye, where will be 

 found the openings of two small ducts (puncta lachrymalia) 

 ready to convey away the superfluous tears. The fluid 

 entering these two short ducts is conveyed by them into the 

 lachrymal sac, which again communicates with the inferior 



Fig. 82.* 



meatus of either nostril by the nasal duct. When this is 

 obstructed, the tears flow over the lower eyelid, constituting 

 the disease called fistula lachrymalis. 



Towards the inner angle of the eye is a small body, called 

 the canmcula lachrymalis ; also a fold of the conjunctiva, 

 which is very small in man, being merely the vestige of a 

 structure which, in some other animals, as in birds, is carried 

 to its highest development. 



[This fold is in fact the rudiment of the third or vertical eye- 

 lid in birds. E. K.] 



245. The structure of this apparatus is pretty nearly 

 the same in all mammals, birds, reptiles, and fishes. The 

 eye in certain mollusca also resembles the eye of animals much 

 higher in the range ; but in most of this class the structure 

 is very different, and as we descend to insects, Crustacea, 



* h, i, punctum lachrymale. The two canals, k and I, open into the 

 lachrymal sac n, which passes off into the lachrymal duct ; Ig, lachrymal 

 gland ; p, pupil ; ir, iris ; c, cornea ; cl, caruncula lachrymalis ; up, upper, 

 and un, under eyelid. 



