OBSERVATIOXS OST VISION. 



5^Z5 



these pracesses are yet more incapable of 

 drawing back the crystalhne, and such an 

 action is equally inconsistent with observa- 

 tion. 



Some other suppositions have also been 

 formed by different physiologists. Zinn ima- 

 gines the ciliary processes to be distended by 

 a fluid, and to protrude the lens. Sauvages 

 eOBJectures, that the ring of Petit is inflated 

 by the electric fluid, and alters the form of 

 ^e Jpns: Moulin, .that the cornea is rendered 

 ipofo convex by its ligaments, which are in 

 fact nerves : Bourdelot, that the contraction 

 of the pupil increases the convexity of the 

 lens. But all these opinions are liable to as 

 strong objections as those which I have al- 

 ready examined. 



From these considerations, and from the 

 observations of Dr. Porterfield and others, 

 that those who have been couched have 

 no longer the power of accommodating the 

 eye to different distances, 1 had concluded 

 that the j'ays of light, emitted by objects at a- 

 small distance, could only be brought to foci 

 on the retina by a nearer approach of the 

 crystalline to a spherical form ; and I could 

 imagine no other power capable of produc- 

 ing this change than a muscularit}' of a part, 

 or the whole, of its capsule. 



But in closely examining, with the naked 

 eye, in a strong light, the crystalline from an 

 ox, turned out of its capsule, I discovered a 

 structure, which appears to remove all the 

 difficulties with which this branch of optics 

 has long been obscured. On viewing it with 

 a magnifier, this structure became more evi- 

 dent. 



The crystalline lens of the ox is an orbicu^ 

 lar, convex, transparent body, composed of 

 a considerable number of similar coats, of 

 which the exterior closely adhere to the inte- 



rior. Each of these coats consists of six series 

 of fibres, intermixed with a gelatinous sub- 

 .stance, and attached to six lines, which have 

 somewhat of a membranous appearance. 

 Three of these lines or tendons are anterior, 

 three posterior ; their length is about two 

 thirds of the sernidiameter of the coat; their 

 arrangement is that of three equal and equi- 

 distant rays, meeting in the axis of the crys- 

 talline ; one of the anterior is directed to- 

 wards the outer angle of the eye, and one of 

 the posterior towards the inner angle, so that 

 the posterior are placed opposite to the middle 

 of tile interstices of the anterior; and planes 

 passing through each of the six, and through 

 the axis, would mark on either surface six re- 

 gular equidistant rays. The fibres arise from 

 both sides of each line; they diverge till 

 they reach the greatest circumference of the 

 coat, and having passed it, they again con- 

 verge, till the}' are attached respectively to 

 the sides of the nearest lines of the opposite 

 surface. The anterior or posterior portion of 

 the six, viewed together, exhibits the appear- 

 ance of three penniformiradiated muscles. 

 The anterior lines of attachment of all the 

 coals are situated in the same planes, and the 

 posterior ones in the continuations of tliese 

 planes beyond the axis. Such an arrange-: 

 ment of fibres can be accounted for on no 

 other supposition than that of muscularity. 

 Thismassis inclosed in a strong membranous 

 capsule,to which it is loosely connected by mi- 

 nute vessels and nerves ; and the connexion 

 is more observable near its greatest circum- 

 ference. Between the mass and its capsule is 

 found a considerable quantity of an aqueous 

 fluid, the liquid of the crystalline. 



r conceive, therefore, that when the will 

 is exerted to view an object at a small dis- 

 tance, the influence of the mind is conveyed , 



