PRELIMINARY ANATOMICAL AND HISTOLOGICAL OBSERVATIONS. 821 



Lens-fibers. 



layer of low, cuboidal cells. Toward the equator of the lens these cells become 

 elongated into mon enucleated fibers, all of which bend around the margin of the 

 lens, and meet on both sides of the lens, their ends forming a stellate figure (lens- 

 star), and being held together by a cement-substance. The lens-fibers contain 

 globulin, enclosed in a sort of sheath. They are flattened mutually into hex- 

 agonal fibers, those of the central layers having their edges interlocked by means 

 of toothed projections. 



For the sake of simplicity, the lens may be considered as a biconvex body, 

 with spherical surfaces, the posterior surface having the greater curvature. The 

 anterior surface, however, really represents a part of an ellipsoid, produced by 

 rotation about the short axis. The posterior surface resembles the vertical 

 section of a paraboloid, that is it may be considered as produced by the rotation 

 of a parabola about its axis. The outer layers of the lens have a lower index of 

 refraction than the more internal layers. The central nucleus is of greater 

 density than the lens as a whole, and it is, at the same time, more convex. The 

 edge of the lens is always separated by an interspace from the ciliary process. 



The zonule of Zinn, which arises from the ora serrata, is applied to the ciliary 

 portion of the choroid in the form of a ruffled, folded membrane, in such a way 

 that the ciliary processes occupy its folds, and are attached to them. It then 

 passes to the edge of the lens, on the anterior 

 portion of which it is inserted in a wavy man- 

 ner. Behind the zonule of Zinn, reaching 

 to the vitreous body, is the canal of Petit. 

 The zonule is a fibrous fenestrated mem- 

 brane; according to Merkel and H. Virchow, 

 the canal of Petit also is occupied by exceed- 

 ingly fine fibers: it is consequently not a 

 true canal, but a complicated system of 

 communicating spaces. The zonule is always 

 stretched and keeps the lens in position, so 

 that it may be considered as the suspensory 

 ligament of the lens. 



Opacities of the lens (gray cataract) hinder 

 the entrance of rays of light into the eye. 

 The absence of the lens (aphakia) , following 

 operations for cataract, may be compensated 

 by the use of strong convex glasses. Such an 

 eye, of course, possesses no power of accom- 

 modation. The lens contains albuminoid 

 bodies, some of which are soluble in water 

 and sodium chlorid (chiefly globulin and some 

 albumin) and some insoluble. 



The vitreous body is invested by the 

 transparent hyaloid membrane, the outer 



surface of which, as far forward as the ora serrata is in contact with the internal 

 limiting membrane of the retina. From this point forward the meridional fibers 

 of the zonule of Zinn arise between the two, and are adherent to the surface of 

 the vitreous and to the ciliary processes. A canal, 2 mm. in diameter, the 

 hyaloid canal, runs from the optic papilla to the posterior surface of the lens; 

 in fetal life it is occupied by blood-vessels. The peripheral portion of the vitreous 

 body is laminated like an onion. The central portion is homogeneous. In the 

 former, especially in newborn infants, there are spherical (leukocytes), spindle- 

 shaped, or stellate, and also vacuolated cells of mucoid tissue; in the center 

 there are only disintegrated remains of these cells. Running between them are 

 transparent fibers and lamellae. The vitreous body is gelatinous in character, 

 and contains only i.i per cent, of solids, consisting of mucin, with albumin, 

 and traces of globulin and glutin. 



The lymph-tracts of the eye include an anterior and a posterior set. The 

 anterior is composed of the anterior and posterior chambers, which communicate 

 with the lymph-vessels of the iris, the ciliary processes, the sclera, the cornea and 

 the conjunctiva. The posterior chamber communicates with the canal of Petit. 



To the posterior lymph-system belongs, in the first place, the hyaloid canal, 

 and secondly the large pcrichoroidal space situated between the sclera and the 

 choroid. The latter communicates by means of lymph-vessels, which surround 

 the emerging trunks of the vorticose vessels of Stenon, with the large lymph -space 



Polygonal transverse 



sections of lens-fibers. 



FIG. 270. 



