194 



EYE. 



raising by this means the folds from the hyaloid 

 membrane. It is difficult, however, to pre- 

 serve the air in these folds for any length of 

 time under water, because the tendency of 

 the air to ascend causes the rupture of the 

 membrane, by which it is allowed to escape. 

 After the lens, included in its proper capsule, 

 has been detached from its situation on the 

 vitreous humour, the space it occupied pre- 

 sents the appearance of a circular depression, 

 surrounded by those productions of the hyaloid 

 membrane of which I have just spoken ; the 

 vitreous humour remaining in every respect 

 perfect, notwithstanding this abstraction of the 

 lens." ' 



M. Ribes, in the Memoires de la Socie"te 

 Medicale d'Emulation for 1816, describes the 

 ciliary processes of the vitreous humour as 

 follows. " At the anterior part of the vitreous 

 humour, and at a short distance from the cir- 

 cumference of the crystalline, may be seen a 

 ciliary body almost altogether similar to that 

 of the choroid, and which has been named by 

 anatomists corona ciliaris, but no writer has 

 hitherto pointed out its structure, or the impor- 

 tant office it appears to perform. Each of 

 these processes has a margin adherent to the 

 vitreous humour, and encroaches a little on the 

 circumference of the lens. It appears to me 

 impossible to ascertain whether the surfaces are 

 reticulated, but they are villous. The free 

 margin is obviously fringed, and presents 

 nearly the variety of appearance observed in 

 the fringes of ciliary processes (of the choroid) 

 of different animals examined by me, except 

 that the summits are black ; the interval which 

 separates each process of the vitreous humour 

 is a species of depressed transparent gutter. 

 The black colour of the free margins and the 

 transparency of the space which separates each 

 ciliary process adorns the anterior part of the 

 vitreous humour with a circle remarkable for 

 its agreeable effect, and which has been com- 

 pared to the disc of a radiated flower." Dr. 

 Knox, in a communication made to the Royal 

 Society of Edinburgh, at the same time that 

 mine was made to the Medico-Chirurgical 

 Society, describes the ciliary processes of the 

 choroid as follows : u In whatever way, the 

 membrane or assemblage of membranes pro- 

 ceeds forwards to be inserted into the circum- 

 ference of the capsule of the lens, forming in 

 its passage numerous longitudinal folds, and 

 small projecting fimbriated bodies, by which, 

 in a natural state, the transparent humours are 

 connected with the superjacent ciliary body (of 

 the choroid) ; when examined with a good 

 glass, these folds are remarkably distinct, and 

 the whole bears the closest resemblance in its 

 distribution to the true ciliary body and pro- 

 cesses. I have, therefore, ventured to call 

 them the internal or transparent ciliary body, 

 or the ciliary body of the hyaloid membrane, 

 in contradistinction to that of the choroid." It 

 must not be forgotten that these ciliary pro- 

 cesses of the hyaloid membrane were described 

 by Monro in his Treatise on the Eye, and are 

 strongly marked in a coarsely executed plate. 

 lie considered that the retina was continued, to 



the lens, and describes its course under the 

 ciliary processes of the choroid ; thus " on ex- 

 amining the retina with still greater accuracy, 

 it appears that it has exactly the same number 

 of folds or doublings that the choroid coat has; 

 for it enters double between the ciliary pro- 

 cesses, nearly in the same way that the pia 

 mater enters into the coats of the brain. The 

 furrows and doublings of the retina, which, if 

 we are to use the favourite term ciliary, may 

 be called its ciliary processes, make an impres- 

 sion on the anterior part of the vitreous hu- 

 mour." The structure alluded to was also 

 observed by Hovius nearly an hundred years 

 before. 



From the preceding observations respecting 

 the ciliary processes of the vitreous humour, it 

 may justly be inferred that the ciliary pro- 

 cesses of the choroid, and these ciliary pro- 

 cesses of the vitreous humour, are of the same 

 nature, differing only in those of the choroid 

 receiving red blood, while those of the vitreous 

 humour receive a transparent fluid by their 

 bloodvessels. The adaptation of these two 

 circles of folds to each other appears to be a 

 most beautiful example of mechanical con- 

 struction occurring in soft parts : it is a species 

 of dovetailing of the one structure into the 

 other, by which an intimate union is secured 

 between one part of considerable strength and 

 another of extreme delicacy. A connexion 

 equally perfect is established between the ex- 

 ternal surface of the choroid at its margin, and 

 the corresponding margin of the sclerotic, by 

 means of the ciliary ligament; in fact, with- 

 out these two provisions of ciliary ligament 

 and ciliary processes, and their application 

 between the sclerotic, choroid, and vitreous 

 humour, the chambers of the eye must be 

 imperfectly constructed, and the optical me- 

 chanism of the organ defective. It is the 

 mechanical bond between these dissimilar parts 

 which perfects the chamber of aqueous humour, 

 and prevents that fluid from escaping, either 

 between the sclerotic and choroid, or between 

 the choroid and vitreous humour. 



Of the crystalline lens. It has been al- 

 read*y stated, that there is a double convex 

 lens within the sphere of the eye, at a short 

 distance behind the external lens or cornea. 

 This is the crystalline lens or crystalline 

 humour, which gives additional convergence 

 to the rays of light transmitted through the 

 pupil. It is placed in a depression, formed for 

 its reception on the anterior, compressed, or 

 truncated portion of the vitreous humour, 

 where that body approaches the back of the 

 iris, and constitutes part of the boundaries of 

 the posterior chamber of the aqueous humour. 

 In this depression it adheres firmly to the hya- 

 loid membrane, and from the vessels of that 

 structure derives its nutriment. 



This double convex lens does not present the 

 same curvature on both surfaces, the anterior 

 being less curved than the posterior, in the 

 ratio of about 4 to 3. Attempts have been made 

 to determine with accuracy the nature of these 

 curvatures, first by Petit, and subsequently by 

 Wintringham, Chossat, ana! others. The re- 



