64 SPECIAL SENSES. 



passes forward to become continuous with the anterior por- 

 tion 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 corru- 

 gated, or thrown into folds which correspond with the cili- 

 ary processes, with which it is in contact. This corrugated 

 portion is called the zone of Zinn. The two layers thus 

 surround the lens and are properly called its suspensory 

 ligament. As the two layers of the suspensory ligament sep- 

 arate at a certain distance from the lens, one passing to the 

 anterior and the other to the posterior portion of the capsule, 

 there remains a triangular canal, about -^ of an inch 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 very small quantity of clear liquid. 



As we have already remarked in describing the retina, at 

 the ora serrata, the membrane is closely connected, by a mu- 

 tual interlacement of fibres, with the suspensory ligament. 

 It is important to appreciate clearly the relations of the sus- 

 pensory ligament, in order to understand the mechanism of 

 accommodation of the lens to vision at different distances. 

 The ciliary muscle being in repose, during what is termed 

 the indolent condition of the eye, when it is adapted to vision 

 at long distances, the tension of the parts flattens the lens ; 

 but, in the effort of accommodation for near objects, the 

 ciliary muscle contracts, compresses the contents of the globe, 

 relaxes the suspensory ligament, and the inherent elasticity 

 of the lens renders it more convex. It is by a delicate use 

 of this muscle, that the proper adaptation of the curvatures 

 of the lens is obtained. 



The membrane forming the suspensory ligament is com- 

 posed of pale longitudinal and transverse fibres of rather a 

 peculiar appearance, which are much less affected by acetic 

 acid than the ordinary fibres of connective tissue. 



Aqueous Humor. The space bounded in front by the cor- 



