AQUEOUS HUMOUR. CRYSTALLINE HUMOUR. 501 



stained by the pigmentum nigrum of the ciliary processes. They 

 derive their vessels from the vascular layer of the retina. The under 

 surface of the zonula is in contact with the hyaloid membrane, and 

 around the lens forms the anterior fluted^ wall of the canal of Petit. 



The connection between these folds and the ciliary processes may 

 be very easily demonstrated by dividing an eye transversely into two 

 portions, then raising the anterior half, and allowing the vitreous 

 humour to separate from its attachment by its own weight. The folds 

 of the zonula will then be seen to be drawn out from between the folds 

 of the ciliary processes. 



HUMOURS. The Aqueous humour is situated in the anterior and 

 posterior chambers of the eye ; it is a weakly albuminous fluid, having 

 an alkaline reaction, and a specific gravity very little greater than dis- 

 tilled water. According to Petit, it scarcely exceeds four or five 

 grains in weight. 



The anterior chamber is the space intervening between the cornea 

 in front, and the iris and pupil behind. The posterior chamber is the 

 narrow space, less than half a line in depth,* bounded by the posterior 

 surface of the iris and pupil in front, and by the ciliary processes, 

 zonula ciliaris, and lens behind. The two chambers are lined by a 

 thin layer, the secreting membrane of the aqueous humour. 



The Vitreous humour forms the principal bulk of the globe of the 

 eye. It is an albuminous fluid resembling the aqueous humour en- 

 closed in a delicate membrane, the hyaloid, which sends processes 

 into its interior, forming areolae in which the humour is retained. A 

 small artery may sometimes be traced through the centre of the 

 vitreous humour to the capsule of the lens; it is surrounded by a 

 tubular sheath of the hyaloid membrane. This vessel is easily inject- 

 ed in the foetus. 



The Crystalline humour or lens is situated immediately behind the 

 pupil, and is surrounded by the ciliary processes which slightly over- 

 lap its margin. It is more convex on the posterior than on the 

 anterior surface, and is embedded in the anterior part of the vitreous 

 humour, from which it is separated by the hyaloid membrane. It is 

 invested by a peculiarly transparent and elastic membrane, the capsule 

 of the lens, which contains a small quantity of fluid called liquor 

 Morgagni^ and is retained in its place by the attachment of the 

 zonula ciliaris. Dr. Jacob is of opinion that the lens is connected to . 

 its capsule by means of areolar tissue, and that the liquor Morgagni 

 is the result of a cadaveric change. 



The lens consists of concentric layers, of which the external are 



* Winslow and Lieutaud thought the iris to be in contact with the lens ; it 

 frequently adheres to the capsule of the latter in iritis. The depth of the pos- 

 terior chamber is greater in old than in young persons. 



t John Baptist Morgagnfwas born in 1682. He was appointed Professor 

 of Medicine in Bologna, and published the first part of his " Adversaria Ana- 

 tomica," in 1706. He died in 1771. 



