SIGHT. 



like a very tenacious, although an amazingly clear, glue. Its 

 nucleus is more dense than the exterior laminae. The laminae may 

 be reduced into extremely delicate fibres, converging from the 

 circumference to the centre. 8 



" In an adult man the lens is proportionally to the whole body 

 smaller than in quadruped mammalia ; also less convex, especially 

 on its anterior surface. 



" The remaining space of the eye is filled by the aqueous hu- 

 mour, which is very limpid, and divided by the iris into two cham- 

 bers ; the anterior and larger separating the cornea and iris ; 

 and the posterior, in which the uvea lies towards the corpus ci- 

 liare, so small as scarcely believed by some to exist. 



" These most valuable parts are defended from injury both by 

 the depth of their situation in the orbits and by the valvular 

 coverings of the eye-lids, 



" In the duplicature of the palpebr&, lie the sebaceous follicles 

 of Meibomius 1 , thickly distributed: and their edges are fringed 

 by a triple or quadruple series of cilia* : the cartilaginous tarsi 

 serve for their support and expansion, and also facilitate their mo- 

 tion upon the eye-ball. 



" Above the eyelids, to use the language of Cicero, are placed 

 the supercilia, which preserve the eyes from the sweat flowing 

 from the head and forehead, and in some measure screen them 

 from too strong a light. 



" To lubricate the eyes, to preserve their brightness, and to 

 wash away foreign matters, is the office of the tears ; the chief 

 source of which is a conglomerate gland placed in the upper and 

 exterior part of the orbit. It has numerous but very fine excre- 

 tory ducts, which are said to discharge about two ounces of 

 tears upon each eye during the twenty-four hours : the tears are 

 afterwards absorbed by the puncta lachrymalia, the function of 

 which may, in a certain sense, be compared to that of the lacteals 

 in the villous coat of the small intestines ; from the puncta they 

 are conveyed through the snail's horns, as they are called, into 



8 " Th. Young, Phil. Trans. 1795, tab. xx. fig. 2,3. 



Dav. Hosack, ib. 1794, tab. xvii. fig. 4. 



J. C. Reil, De lends crystallines structurafibrosa. Hal. 1743. 8vo." 



* " H. Meibomius, De vasis palpebrarum novis ep. Helmst. 1666. 4to.'* 



u " B. S. Albinus, Annotat. Academ. 1. iii. tab. iii. fig. 4." 



p p 3 



