33* On the Mechamfm of the Eye. 



ance; although it requires a good micrpfcope to difcover it diflimSly : but the zone maybe 

 eafily peeled off under water, and hardened in fpirits. Its ufe is uncertain ; but it may 

 poflibly fecrete the liquid of the cryftalline ; and it as much deferves the name of a gland, 

 as the greater part of the fubftances ufually fo denominated. In peeling it off, I have very 

 diftinftly obferved ramifications, which were palCng through it into tlie lens ; (Plate XV. 

 Fig. 50.) and indeed it is not at all difficult to detedt the veffels counefting the margin of 

 the lens with its capfule; and it is furprifmg that M. Petit (hould have doubted of their 

 exiftence. I have not yet clearly difcerned this cryftalline gland in the human eye ; but I 

 infer the exiftence of fomething fimilar to the globules, from the fpotted appearance of the 

 image of a lucid point already mentioned i for wliich I can no otherwife account, than by 

 attributing it to a derangement of thefe particles, produced by the external force, and to 

 an unequal imprefiion made by them on the furface of the lens. 



In birds and in fiflies, the fibres of the cryftalline radiate equally, becoming finer as they 

 approach the vertex, till they are loft in a uniform fubftance, of the fame degree of firm- 

 nefs, which appears to be perforated in the centre by a blood veflel. (Plate XV. Fig. 53 ) 

 In quadrupeds, the fibres at their angular meeting are certainly not continued, as Leeuw- 

 cnhoek imagined, acrofs the line of divifion ; but there does not appear to be any diffimilar 

 fubftance interpofed between them, except that very minute trunks of veflels often mark 

 that line. But, fincc the whole mafs of the lens, as far as it is moveable, is probably en- 

 dued with a power of changing its figure, there is no need of any ftrength of union, or 

 place of attachment, for the fibres, fince the motion meets with little or no refiftance. 

 Every common mufcle, as foon as its contraftion ceafes, returns to its natural form, even 

 without the afflftance of an antagonift j and the lens itfelf, when taken out of the eye, in 

 its capfule, has elafticity enough to re-aflume its proper figure, on the removal of a force 

 that has compreffed it. The capfule is higlily elaftic; and, fince it is laterally fixed to the 

 ciliary zone, it mu(i co-operate in rcftoring the lens to its flatteft form. If it be inquired, 

 why the lens is not capable of becoming lefs convex, as well as more fo, it may be an- 

 fwered, that the lateral parts have probably little contraftive power; and, if they had 

 more, they would have no room to increafe the fizc of the difc, which they muft do, in 

 order to fljorten the axis.; and the parts about the axis have no fibres fo arranged as to 

 {horten it by their own contrailion-. 



I confider myfelf as being partly repaid for the labour loft in fearch of the nerves of the 

 lens, by having acquired a more accurate conception of the nature and fituarlon of the 

 ciliary fubftance. It had already been obferved, that in the hare and in the wolf, the 

 ciliary proceffes are not attached to the capfule of the lens; and if by the ciliary procefles 

 we underftand thofe filaments which are feen detached after tearing away the capfule, and 

 confift of ramifying veffels, the obfervation is equally true of the common quadrupeds, and 

 i will venture to fay, of the human eye *. Perhaps thia remark has been made by others, 



!» yid.HaJl, Phyfiol. V. p. 432. et Duvcrney, ibl cltat. 



but 



