CRYSTALLINE HUMOUR STRUCTURE. 445 



The Crystalline humour or lens is situated immediately behind 

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

 overlap 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 cellular tissue, and that the liquor Mor- 

 gagni is the result of a cadaveric change. 



The Lens^ consists of concentric layers, of which the external are 

 soft, the next firmer, and the central form a hardened nucleus, 

 These layers are best demonstrated by boiling, or by immersion in 

 alcohol, when they separate easily from each other. Another divi- 

 sion of the lens takes place at the same time ; it splits into three tri- 

 angular segments, which have the sharp edge directed to wards, the 

 centre, and the base towards the circumference. The concentric 

 lamella? are composed of minute parallel fibres, which are united 

 with each other by means of scalloped borders ; the convexity on 

 the one border fitting accurately the concave scallop upon the other. 



Immediately around the circumference of the lens is a triangular 

 canal, the canal of Petit,\ about a line and a half in breadth. It is 

 bounded in front by the flutings of the zonula ciliaris ; behind by the 

 hyaloid membrane ; and within by the border of the lens. 



The Vessels of the globe of the eye are the long, and short, and 

 anterior ciliary arteries, and the arteria cen'tralis retinae. The long 

 ciliary arteries, two in number, pierce the posterior part of the scle- 

 rotic, and pass forward on each side, between that membrane and 

 the choroid, to the ciliary ligament, where they divide into two 

 branches, which are distributed to the iris. The short ciliary arteries 

 pierce the posterior part of the sclerotic coat, and are distributed to 

 the internal layer of the choroid membrane. The anterior ciliary 

 are branches of the muscular arteries. They enter the eye through 

 the anterior part of the sclerotic, and are distributed to the iris. It 

 is the increased number of these arteries in iritis that forms the 

 peculiar red zone around the circumference of the cornea. 



The arteria centralis retinez enters the optic nerve at about half 

 an inch from the globe of the eye, and passing through the porus 

 opticus is distributed upon the inner surface of the retina, forming 

 its vascular layer ; one branch pierces the centre of the vitreous 

 humour, and supplies the capsule of the lens. 



The Nerves of the eyeball are the optic, two ciliary nerves from 



* John Baptist Morgagni was born in 1682. He was appointed Professor of Medi- 

 cine in Bologna, and published the first part ef his "Adversaria Anatomica," in 170G. 

 He died in 1771. 



t John Louis Petit, a celebrated French surgeon : he published several surgical and 

 anatomical Essays, in the early part of the 18th century. He died in 1750. 



