EYE, 



201 



the lens and its capsule ; he says, " The cap- 

 sule adheres to the ciliary substance, and the 

 lens to the capsule, principally in two or three 

 points ; but I confess I have not been able to 

 observe that these points are exactly opposite 

 to the trunks of nerves; so that probably the 

 adhesion is chiefly caused by those vessels 

 which are sometimes seen passing to the cap- 

 sule in injected eyes. We may, however, dis- 

 cover ramifications from some of these points 

 upon and within the substance of the lens, 

 generally following a direction near to that of 

 the fibres, and sometimes proceeding from a 

 point opposite to one of the radiating lines of 

 the same surface. But the principal vessels of 

 the lens appear to be derived from the central 

 artery, by two or three branches at some little 

 distance from the posterior vortex, which I 

 conceive to be the cause of the frequent adhe- 

 sion of a portion of a cataract to the capsule 

 about this point ; they follow nearly the course 

 of the radiations and then of the fibres ; but 

 there is often a superficial subdivision of one 

 of the radii at the spot where one of them 

 enters." The great size of the vessels distri- 

 buted on the back of the capsule in the foetus 

 strengthens the conclusion that the lens is fur- 

 nished with vessels as the rest of the body. 

 When the eye of a foetus of seven or eight 

 months is finely injected, a branch from the 

 central artery of the retina is filled and may be 

 traced through the centre of the vitreous hu- 

 mour to the back of the capsule, where it 

 ramifies in a remarkably beautiful manner, 

 assuming, according to Sommerring, a stellated 

 or radiating arrangement. Zinn declares that 

 he found branches from this vessel penetrating 

 the lens : " Optime autem placet observatio 

 arteriolae lentis, in oculo infantis, cujus vasa 

 cera optime erant repleta, summa voluptate 

 mihi visae, quam prope marginem ad convexi- 

 tatem posteriorem dilatam, duobus ramulis 

 perforata capsula in ipsam substantiam lentis 

 profunde se immergentem cortissime con- 

 spexi." He also quotes the authority of 

 Ruysch, Moeller, Albinus, and Winslow, as 

 favouring the same view. Against such au- 

 thority I find that of the French systematic 

 writer Bichat advanced ; but on such a point 

 his opinion is of little 



Fig. 125. 



value. Annexed is 

 Zinn's representa- 

 tion of the distribu- 

 tion of the branch 

 of the central artery 

 on the back of 

 the capsule, from 

 a preparation in 

 Lieberkuhn's mu- 

 seum. Similar fi- 

 gures have been 

 given by Albinus, 

 Sommerring, and 

 Sir Charles Bell. 



Of the aqueous humour. In the preliminary 

 observations at the commencement of this 

 article, I stated that a cavity or space filled 

 with water exists between the cornea and crys- 

 talline lens, in which space the iris is extended, 

 with its aperture or pupil, to moderate the 



quantity of light, and interrupt the passage of 

 the extreme rays. It is bounded anteriorly by 

 the concave inner surface of the cornea, and 

 posteriorly by the crystalline lens and other 

 parts, and is necessarily divided into two 

 spaces or chambers by the iris. That in front 

 of the iris, called the anterior chamber, 19 

 bounded by the concare inner surface of the 

 cornea anteriorly, and by the flat surface of the 

 iris posteriorly, which, I have already stated, 

 is a plane, not a convex surface, as represented 

 in the plates of Zinn and others. The size of 

 this space is necessarily small, and varies in 

 different individuals according to the convexity 

 of the cornea, which also frequently varies. 

 It is always, however, sufficiently large to allow 

 the surgeon to introduce a needle to break up 

 a cataract without wounding the iris or cornea. 

 The posterior chamber is bounded in front by 

 the back of the iris, and behind by the crys- 

 talline lens ; with that portion of the hyaloid 

 membrane of the vitreous humour, which is 

 between the anterior termination of the ciliary 

 processes of the choroid and the circumference 

 of the lens. The circumference of the pos- 

 terior chamber is bounded by the anterior ex- 

 tremities of the ciliary processes of the choroid, 

 as they extend from the vitreous humour to the 

 back of the iris. It does not appear to be 

 generally admitted or well understood that any 

 part of the hyaloid membrane of the vitreous 

 humour enters into the composition of the 

 posterior chamber of the aqueous hu- 

 mour, notwithstanding the decisive opinion 

 and accurate representation of the celebrated 

 Sommerring, in which I entirely concur, as I 

 have stated above in describing the vitreous 

 humour. 



The size of the posterior chamber has been 

 the subject of much discussion and contro- 

 versy, and various attempts have been made 

 by freezing the eye and other means to deter- 

 mine the matter. Petit, after a careful inves- 

 tigation, considered that the distance between 

 the lens and iris was less than a quarter or half 

 a line, in which Haller appears to concur. 

 Winslow, in the Memoirs of the French Aca- 

 demy for 1721, insists that the iris is in contact 

 with the lens. Lieutaud, in his Essais Ana- 

 tomiques, is equally positive on this point, 

 and even denies altogether the existence of a 

 posterior chamber. The question is not an 

 indifferent one, inasmuch as it involves impor- 

 tant considerations as to operations for cataract 

 and inflammations of the iris. Modern ana- 

 tomists appear, generally, to consider the dis- 

 tance between the lens and iris to be greater 

 than it really is. Although I cannot agree 

 with Winslow and Lieutaud that the margin 

 of the pupil is always in contact with the lens, 

 I believe it frequently is so, especially in the 

 earlier periods of life, when the curvatures of 

 the lens are considerable. In iritis adhesions 

 generally take place between the margin of the 

 pupil and the capsule of the lens, a conse- 

 quence not easily accounted for, if the parts 

 be not in contact. In old age the lens be- 

 comes much flattened, and therefore retreats 

 from the pupil, to such a degree that the sha- 



