Chap. 41.] Structure of the Eye. 385 



ciliary edges of the tarfi are furniihed with eye-lafhes. 

 The chief life of thefe feems to be, to prevent duft, 

 and other matters floating in the atmofphere, from fal- 

 ling into the eyes. 



At the internal angle of the eye is fituated the ca- 

 runcula lachrymalis, which is a fmall reddilh oblong 

 body. This fubftance feems to be glandular. By the 

 aid of a microfcope we obferve upon it a great number 

 of fmall hairs, covered by an oily yellowirti matter. Oji 

 the globe of the eye, near this glandular body, is a 

 lemilunar fold formed by the membrana conjunctiva. 

 This fold, which is called the membrana femilunaris, 

 is fhaped like a crcfcent, the two points of which 

 anfwer to the puncta lachrymalia, which are the be- 

 ginnings of a canal terminating in the cavity of the 

 noftrils. 



The furface of the eye Is conftantly moiflened 

 by a very fine limpid fluid, the tears, which are 

 chiefly, and perhaps wholly, derived from a gland; 

 fituated in a fmall depreffion of the os frontis, near 

 the external angle of the eye. Its excretory duels 

 pierce the tunica conjunctiva ju'ft above the cartilagi- 

 nous borders of the upper eyelids. As this fluid enters 

 the eye at the fupterior angle; it naturally defcends 

 towards the inferior, and is alfo frequently fpread over 

 the furface of the eye by the motion of the eyelids. 

 When it arrives, after thus having wafhed the eye, at 

 the internal angle, it is conducted by the membrana 

 femilunaris into the punfta lachrymalia, which lead into 

 the facchus lachrymalis, from which it is ultimately 

 difcharged into the nofe. 



When the eye is irritated by any extraneous fubu 

 fiance, the tears are difcharged in greater quantity, and 

 thus ferve as a defence to this tender organ, and fome- 

 times wafh away the caufe of irritation, or facilitate its 



VO.L. JIL C ttmoval, 



