ORGAN OF VISION. 



221 



vitreous humours ; and Dr. Fi s- 96> 



Arnott, 1 that the anterior 

 and posterior chambers of 

 the eye are the compart- 

 ments before and behind 

 the crystalline. Anato- 

 mists are not agreed, whe- 

 ther the aqueous humour 

 have a proper membrane, 

 which secretes it 5 or whe- 

 ther it be not an exhalation 

 from the vessels of the iris 

 and ciliary processes. M. 

 Kibes derives it from the 

 vitreous humour. Howso- 

 ever secreted, it is very 

 rapidly regenerated when 

 evacuated ; as it must be 

 in every operation for cata- 

 ract by extraction. It is 

 not lodged in cells ; and 

 hence readily flows out 

 when the cornea is punc- 

 tured. The quantity of 

 aqueous humour, in the 

 adult, is about five or six 

 grains. Its specific gravity is not rigorously determined, but it differs 

 slightly from that of water, being a little greater. According to Berze- 

 lius, it is composed of water, 98'10; a little albumen; chlorides and 

 lactates, 1*1.5 ; soda, with a substance soluble in water, 0*75. 



The crystalline lens is a small body, of a crystalline appearance, and 

 lenticular shape, whence its name. It measures, in the adult, about 

 1*33 of an inch in its greatest circumference; and is about 2J lines 

 thick at the centre. It is situate between the aqueous and vitreous 

 humours ; and at about one-third of the antero-posterior diameter of the 

 organ. A depression at the anterior surface of the vitreous humour 

 receives it ; and a reflection of the proper membrane of the humour 

 passes over it. The crystalline is surrounded by its capsule, the inte- 

 rior of which is bathed by a slightly viscid and transparent secretion, 

 called liquor Morgagnii. The lens is more convex behind than before ; 

 the radius of its anterior surface being, according to Sir David Brews- 

 ter, 2 0*30 ; and that of its posterior surface 0*22 of an inch. It con- 

 sists of a number of concentric ellipsoid laminae, increasing in density 

 from the circumference to the centre. Some fibres detach themselves 

 from the different laminae; pass to those immediately beneath, and consti- 

 tute the sole bond of union that exists between them. Of old it was be- 

 lieved that the crystalline was of a muscular structure, and capable of 



Longitudinal Section of the Globe of the Eye. 



1. Sclerotic, thicker behind than in front. 2. Cornea, re- 

 ceived within anterior margin of sclerotic, and connected with 

 it by means of a bevelled edge. 3. Choroid, connected ante- 

 riorly with (4) ciliary ligament, and (5) ciliary processes. 6. 

 Iris. 7. Pupil. 8. Third layer of eye, retina terminating an- 

 teriorly by abrupt border at commencement of ciliary pro- 

 cesses. 9. Canal of Petit, encircles the lens (12); the thin 

 layer in front of this canal is the zonula ciliaris, a prolonga- 

 tion of vascular layer of retina to the lens. 10. Anterior cham- 

 ber of eye containing aqueous humour ; the lining membrane, by 

 which the humour is secreted, is represented in diagram. 11. 

 Posterior chamber. 12. Lens, more convex behind than be- 

 fore, enclosed in its proper capsule. 13. Vitreous humour en- 

 closed in hyaloid membrane, and in cells formed in its interior 

 by that membrane. 14. Tubular sheath of hyaloid membrane, 

 which serves for the passage of the artery of capsule of the 

 lens. 15. Neurilemma of optic nerve. 16. Arteria centralis 

 retinae, embedded in the centre. 



1 Elements of Physics, &c.,-2d Amer. edit., vol. ii. P. i. p. 162, Philad., 1836. 

 * Op. citat., p. 242. See, also, Plulos. Transact, for 1835, p. 3GO.J 



