736 THE EYE. 



In the adult, the anterior surface of the lens becomes more obviously less 

 convex than the posterior ; and the substance of the lens is firmer, colour- 

 less, and transparent. 





o 



Fig. 488. Fig. 488. SIDE VIEWS OF THE LENS AT DIFFERENT AGES. 



h C a, at birth with the deepest convexity ; 6, in adult life 



with medium convexity ; c, in old age with considerable 

 flattening of the curvatures. 



In old age, it is more flattened on both sur- 

 faces ; it assumes a yellowish or amber tinge, and 

 is apt to lose its transparency as it gradually increases in toughness and 

 specific gravity. 



SUSPENSORY LIGAMENT OF THE LENS AND CANAL OF PETIT. 



The suspensory ligament of the lens Retzius (Zonula of Zinn) is a 

 slender but tolerably firm transparent membrane, which, attached to the 

 fore part of the capsule of the lens close to its circumference, passes out- 

 wards to join the hyaloid membrane of the vitreous humour at its most 

 anterior convex part, opposite the ora serrata of the retina, and assists in 

 retaining the lens in its place. On the anterior surface small streaks of 

 pigment are observable after its separation from the other membranes, and 

 when this pigment is removed by washing, small but regular folds processus 

 ciliares zonulse come into view near the lens ; these are plaits in the 

 membrane, and are received into the intervals between the ciliary processes 

 of the choroid coat, into which they fit. Between the folds and the lens- 

 capsule is a slight interval free from plaits, which forms part of the boundary 

 of the posterior aqueous chamber. The posterior surface is turned towards 

 the hyaloid membrane, from which it is separated near the lens by a space 

 named the canal of Petit. 



The suspensory ligament has chemical properties similar to those of the 

 capsule of the lens, but in it parallel or slightly radiating longitudinal fibres 

 may be recognised, which are stiff, elastic, and pale, resembling those of 

 elastic tissue, being less pliable, and less acted on by acetic acid than those 

 of connective tissue. 



Fig. 489. Fig. 489. VIEW FROM BEFORE OF THE CANAL OF PETIT 



INFLATED (from Sappey). 



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

 having been removed, the remaining parts are viewed from 

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

 through an artificial opening. 1, front of the lens ; 2, 

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

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

 dilatations of the canal of Petit. 



The canal of Petit is the interval surrounding 



the edge of the lens-capsule, bounded in front by the suspensory liga- 

 ment, and behind by the hyaloid membrane. Its width is about ^th of 

 an inch. On blowing air into it through an opening in the anterior 

 boundary, the plaits of the suspensory ligament on its front are distended, 

 and the canal presents a sacculated appearance. 



