318 NATURAL THEOLOGY. 



ticed. While the upper eyehd falls, the lower eye- 

 lid is moved towards the nose. This is a part of 

 that curious provision for collecting offensive par- 

 ticles towards the inner corner of the eye. If the 

 edges of the eyelids be marked with black spots, 

 it will be seen that when the eyelids are opened 

 and closed, the spot on the upper eyehd descends 

 and rises perpendicularly, while the spot on the 

 lower eyelid will play horizontally like a shuttle. 



To comprehend these actions of the muscles of 

 the eye, we must remember that the caruncle and 

 membrane called semilunaris, seated in the inner 

 corner of the eye, are for ridding the eye of extra- 

 neous matter, and are, in fact, for the same pur- 

 pose as that apparatus which is more perfect in 

 beasts and birds. The tears are imbibed by the 

 puncta or orifices, which may be seen in the inner 

 corner of the eye : and a tube, formed on the prin- 

 ciple of a siphon, carries them into the nose: whilst 

 the dust, washed to this corner, is thrown out by 

 the apparatus which we have described. 



The course of our inquiry makes some notice of 

 these parts necessary. 



In quadrupeds there is a gland for secreting a 

 glutinous and adhesive fluid, seated on the side of 

 the orbit next the nose : it is quite distinct from 

 the lachrymal gland ; it is squeezed by an appa- 

 ratus of muscles, and the fluid exudes upon the 

 surface of the third eyelid. This third eyelid is a 

 very peculiar part of the apparatus of protection. 

 It is a thin cartilage, the posterior part of which 



