598 



ON THE MECHANISM OF THE EVE. 



gined, that I had succeeded ; but I cannot 

 positively go further than to state my full 

 conviction of tlicir existence, and of the pre- 

 cipitancy of those who have absolutely de- 

 nied it. Tbe long nerves, which are very 

 conspicuous between the choroid and sclero- 

 tic coats, divide each into two, three, or 

 more branches, at the spot where tbe ciliary 

 xone begins, and seem indeed to furnish the 

 choroid with some fine filaments at the same 

 place. The branches often reunite, willi a 

 slight protuberance, that scarcely deserves 

 the name of a ganglion : here they are tied 

 down, and mixed with the hard whitish 

 brown membrane, that covers the compact 

 spongy substance, in which the vessels of the 

 ciliary processes anastomose and subdivide. 

 (Plate 12. Fig. 94.) The quantity of the 

 nerves, which proceeds to the iris, appears to 

 he considerably smaller than thai which ar- 

 rives at the place of division; hence there 

 can be little doubt, that the division is cal- 

 culated to supply the lens with some minute 

 branches ; and it is not improbable, from the 

 appearance of the parts, that some fibres may 

 pass to the cornea; although it might more 

 naturally be expected, that the tunica con- 

 jmictiva would be supplied from v\ iihout. 

 But the subdivisions, which probably pass to 

 the lens, enter immediately into a mixture of 

 ligamentous substance, and of a tough 

 brownish membrane ; and I have not hither- 

 to been able to develope them. Perhaps ani- 

 mals may be found, in which this substance 

 is of a different nature ; and I do not despair 

 that, with the assistance of injections, for 

 more readily distinguishing the blood vessels, 

 and of an acid for whitening the nerves, 

 it may still be possible to trace them in qua- 

 drupeds. Our inability to discover them is 



scarcely an argument against their existence: 

 they must naturally ba delicate and trans- 

 parent ; and we have an instance, in the 

 cornea, of considerable sensibility, where 

 no nerve has yet been traced. The capsule 

 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 op- 

 posite to the trunks of nerves ; so that, pro- 

 bably, the adhesion is chiefly caused by those 

 vessels which are sometimes seen passing to 

 the capsule in injected eyes. We ma3', how- 

 ever, discover ramifications from some of 

 these poiutb', upon and within the substance 

 of the lens, (Plate 1?. Pig. 95.) generally 

 following a direction near to that of the 

 fibres, and sometimes proceeding i'iom 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 blanches at 

 some little distance from the posterior ver- 

 tex ; which I conceive to be the cause of the 

 frequent adhesion of a portion of a cataract 

 to the capsule, about this point : they fol- 

 low nearly the course of the radiiiiions, and 

 then of the fibres ; but there is often a s-ujier- 

 ficial subdivision of one of the radii, at the 

 spot where one of them enters. The vessels 

 coming from the choroid appear principally 

 to supply a substance, hitherto unobserved, 

 which fills up the marginal part of the cap- 

 sule of the crystalline, in the form of a thin 

 zone, and makes a slight elevation, visible 

 even through the capsule. (Fig. 96. . 98.) 

 It consists of coarser fibres than the lens, but 

 in a direction nearly similar ; they are often 

 intermixed with small globules. In some 

 animals, the margin of the zone is crenated. 



