On the Mechanifm ef the Eyf. 55ft 



tliree, or more branches, at the fpot where the ciliary zone begins, and feem indeed to 

 furnifli the choroid with fome fine filaments at the fame place. The branches often re- 

 unite, with a flight protuberance, that fcarcely deferves the name of a- ganglion : here they 

 are lied down, and mixed with the hard whitifh-brown membrane that covers tlie compaft 

 fpongy fubftance, in which the velTels of the ciliary procefles anaftomofe and fubdivide^ 

 (Plate XV. Fig. 47.) The quantity of the nerves which proceeds to the iris, appearstii 

 be confiderably fmaller than that which arrives at the place of divifion : hem:e there can Wo? 

 little doubt that the divifion is calculated to fupply the lens with fome minute brancRe^v 

 and it is not improbable, from the appearance of the parts, that foiT»e fibres may pafs tt) 

 the cornea; although it might more naturally be expefted, that the' ttinic^ conjun£liv4 

 would be fupplied from without. But the fubdivifions which probably pafs to t^iS ifeSSV^ 

 enter immediately into a mixture of ligamentous fubftance, and of a tough brownilh mem- 

 brane; and 1 have not hitherto been able to develope them. Perhaps animals maybe found 

 in which this fubftance is of a difterent nature ; and I do not defpair that, with the affift- 

 ance of ijijeflions, for more readily diftinguifhing the blood velTels, it may ftill be poffibltt 

 to trace them in quadrupeds. Our inability to difcover them, is fearcely an argumetit 

 againil their exiftcnce: they muft naturally be delicate and tranfparent ; and we have a« 

 jnftance, in the cornea, of confiderable fenfibility, where no nerve has yet beeri traced: 

 The capfule adheres to the ciliary fubftance, and the lens to the capfuk, princfpally in twb 

 or three points; but I confefs, I have not been able to obferve that tlitefe points' are exadVIy 

 oppofite to the trunks of nerves ; fo that, probably, the adhefion is chiefly caufed by thofd 

 veflels which are fometimes feen paflirtg to the capfule in injefted e^es, Wtf^may, how- 

 ever, difcover ramifications from fome of thefe points, upon arid \*''ithlri thd fubftance of 

 the lens, (Plate XV. Fig. 48.) generally foWowing a direftioh ne^r to that of the fibresj 

 and fometimes proceeding from a point oppofite to one of the' radiating lines of the fame 

 furface. But the principal veflels of the lens appear to be derived from the cefltr&l attei-yi 

 by two or three branches at fome little diftance from the pofterior Vertex ; which I'dbtf* 

 ceive to be the caufe of the frequent adhefion of a portion of a catarAiSb to the capfulfcj. 

 about this point: they follow nearly the courfe of the radiations, arid therf oF the fibres; 

 but there is often a fuperficial fubdivifion of one of the'radii; ar tlfc ' fpot AiWfcre one- bi 

 them enters. The veflels coming from the choroid appear- principally to fu^ly a fub- 

 ftance, hitherto unobferved, which fills up the marginal patt of the capfule of the cry- 

 ftalline, in the form of a thin zone, and makes a flight eleVatioii> vifible even thrbugh the 

 capfule, (Fig. 49 — 51.) It confifts of coarfer fibres -than- t^Ke'ler^s, but ■"}*'■ a'-<}MdiStibi* 

 nearly fimilar ; they are often intermixed with fmall globules.- ' lir R>theanit«ars> tlie 'ttaif'' 

 j«in of the zone is crenated, efpecially behind, where it is ftiorter': this is obre^Vable itr the 

 partridge; and, in the fame bird, the whole furface of the lens isf feert to be covered with 

 points, or rather globules, arranged in regular lide^j!'(PlAtxi-XV^.' Fig. ^-a.) fofn^ to iliavtf 

 fomewhat the appearance of a honeycomb, but towards the vertex lefs uniformly difpofed. 

 This regularity is a fuHicient proof that there could be no optlcar deception in the appear- 



U u 2 auce ; 



