C22 



THE EYE. 



According- to another and more generally received account the hyaloid mem- 

 brane divides in front into two layers ; an anterior, continued forwards as the 

 zonule of Zinn, and a posterior, passing behind the lens ; the canal of Petit being 

 contained between them. 



Fiff. 432. 



Fig. 432. — View from before op the Canal of Petit 

 INFLATED (from Sajipey). 



The anterior parts of tlie sclerotic, choroid, iris and cornea 

 having lieen removed, tlie remaining parts are viewed from 

 liefore, and the canal of Petit has been inflated with air 

 tln-ough an artificial opening. 1, front of the lens ; 2, 

 vitreous body ; 3, outer border of tiie canal of Petit ; 4, outer 

 part of the zonule of Zinn ; 5, appearance of sacculated 

 dilatations of the canal of Petit. 



THE LENS. 



The lens (kns crijstalUna) is a transparent solid body, of a doubly 

 ^jnvex shape, with the circumference rounded off. It is completely 

 enclosed by a transparent elastic membrane known as the capsule of 

 the Ions. The anterior surface is in contact with the iris towards the 



conv^ 



pupil, receding from it slightly at the circumference ; the poster 



lor 



•iija. 



-OtJTLINEb ILLUilTRATIKG THE CoUUSE OF THE FuillES IN THE F(ETAL 



Crystalline Lens. I 



This diagram represents the typical or more simple state of the fibres in the fuU- 

 gi'own fcetal or infantile condition ; the three dotted lines radiating at equal angles of 

 120° from the centre indicate the position of tlie intersecting planes, where they reach 

 the surface ; the figures 1, 2, 3, 4, 5, and 6, indicate certain fibres selected arbitrarily at 

 equal distances in one-sixth part of the lens to show their course from the front to the 

 baclv ; A, the anterior surface ; B, the posterior surface ; C, the lateral aspect : in these 

 several figiu-es, for the sake of clearness, a few lines only are mtroduced into the ujjper 

 third, while in the lower two-thirds a greater numlier are marked ; but no attempt is 

 made to represent tlie number existing in nature ; the parts of the dotted line marked 

 c, are on a level with the centre of the several lenses. 



rests closely on the vitreous body. Around the circumference is the 

 canal of Petit. Its convexity is not alike on the two surfaces, being 

 greater behind ; moreover, the curvature is less at the centre than 

 towards the margin. It measures about ^rd of an inch across, and 

 -^th from before backwards. In a fresh lens, divested of its capsule. 



