THE EYE AND ITS APPENDAGES 243 



Between the retina and the vitreous, and enclosing the latter 

 except in front, is a thin capsule, the hyaloid membrane. 



This membrane passes forwards in front to the anterior 

 part of the margin of the lens. It becomes stronger in this 

 part, and is called the zonule of Zinn, the zonula ciliaris, or the 

 suspensory ligament of the lens. 



The zonule commences near the ciliary processes, and 

 passes forwards to the front of the lens, and is attached in 

 front to the lens capsule. In addition some fibres are attached 

 to the extreme edge of the lens, and others become continuous 

 with the posterior part of the capsule. 



The interstices between these fibres are occupied by fluid, 

 but after death they may be distended with air, and an 

 appearance of a canal (canal of Petit) encircling the lens is 

 produced. 



Extending forwards from the optic disc through the vitreous, 

 as far as the capsule of the lens, is the canal of Stilling, or 

 hyaloid canal, which is the remains of a passage for a branch 

 from the central artery of the retina in the foetus. 



The lens is a transparent bi-convex body enclosed in 

 a transparent membrane, the lens capsule. It is in contact 

 anteriorly with the iris ; posteriorly it rests in a depression 

 in the vitreous body, and it is surrounded by the suspensory 

 ligament or zonule of Zinn. It is about inch in diameter, 

 and about \ inch thick. 



The lens capsule is the structureless membrane enclosing 

 the lens, thick in front near its circumference, where it is 

 strengthened by the fibres of the zonule, but very thin 

 posteriorly. 



The aqueous humour and the aqueous chambers. The 

 aqueous humour occupies the space between the anterior 

 surface of the lens capsule and the posterior surface of the 

 cornea. 



The iris divides the chamber into two parts, known as the 

 anterior and posterior chambers. 



The anterior chamber is bounded in front by the cornea, 

 behind by the iris, and opposite the pupil by the anterior 

 part of the lens. 



The posterior chamber is the triangular interval at the cir- 

 cumference of the lens between the ciliary processes, the iris, 

 and the zonule of Zinn, 



16 a 



