CRYSTALLINE LENS 663 



ox, cholesterin was found in the proportion of 0.907 of a part per 1000 

 (Flint). In some cases of cataract, cholesterin exists in the lens in a 

 crystalline form ; but under normal conditions it is united with the 

 other constituents. 



Suspensory Ligament of the Lens {Zone of Zinn). The vitreous 

 humor occupies about the posterior two-thirds of the globe and is 

 enveloped in a delicate capsule called the hyaloid membrane. In the 

 region of the ora serrata of the retina this membrane divides into two 

 layers. The posterior layer lines the depression in the vitreous humor 

 into which the lens is received. The anterior layer passes forward 

 toward the lens and divides into two secondary layers, one of which 

 passes forward to become continuous with the anterior 

 portion of the capsule of the lens, while the other 

 passes to the posterior surface of the lens to become 

 continuous with this portion of its capsule. The 

 anterior of these layers is corrugated or thrown into 

 folds that correspond with the ciliary processes, with 

 which it is in contact. This corrugated portion is 

 called the zone of Zinn. The two layers thus sur- 



* i, crystalline lens; 2, 



round the lens and are properly called its suspensory 2, vitreous humor ; 3,3, 



ligament. As the two layers of the suspensory liga- 



ment separate a certain distance from the lens, one zone of zinn, thrown 



,i i __i ,1 ^i into folds; 5, 6, 6, an- 



passing to the anterior and the other to the posterior terior and m jddie por- 

 portion of the capsule, there remains a triangular tions of the zone of 

 canal, about -^ of an inch (2.5 millimeters) wide, 

 surrounding the border of the lens, called the canal of Petit. Under 

 natural conditions the walls of this canal are nearly in apposition, and 

 it contains a small quantity of clear liquid. 



The membrane forming the suspensory ligament is composed of pale 

 longitudinal and transverse fibres of rather a peculiar appearance, which 

 are much less affected by acetic acid than fibres of ordinary connective 

 tissue. 



Aqueous Humor. The space bounded in front by the cornea, 

 posteriorly, by the crystalline lens and the anterior face of its suspen- 

 sory ligament, and at its circumference, by the tips of the ciliary pro- 

 cesses, is known as the aqueous chamber. This contains a clear liquid 

 called the aqueous humor. The iris separates this space into two 

 divisions, which communicate with each other through the pupil ; 

 namely, the anterior chamber, situated between the anterior face of the 

 iris and the cornea, and the posterior chamber, between the posterior 

 face of the iris and the crystalline. It is evident, from the position of 

 the iris, that the anterior chamber is much the larger ; and, indeed, the 



