THE EYE. 757 



tinuous, witliout any line of demarcation, ^Yith the pigmentary layer, 

 the clear cells being gradually replaced by cells containing pigment. 



Excepting these cells, the zonula is a thin, transparent but tolerably 

 firm membrane, stretching from the ora serrata retincc as far as the 

 border of the lens, and appearing to be a continuation of the hyaloid 

 membrane. It consists of peculiar, pale fibres, already very Avell cha- 

 racterized by Ilcnle, resembling certain forms of reticular connective 

 tissue, except that they arc more rigid, usually present no distinct 

 fibrils, and are less swollen in acetic acid. They commence, very fine, 

 a little behind the ora serrata retince on the outer side of the hyaloid 

 membrane, although most intimately connected with it, in part like 

 fibrils of connective tissue, then run forwards, forming a layer at first 

 more lax, and becoming more and more dense, and increasing in thick- 

 ness (up to 0-004 or even 0-01 of a line and more), with numerous divi- 

 sions and anastomoses, and for the most part parallel with each other, 

 until they constitute, at the free portion of the zonula, a perfect, con- 

 tinuous layer — though still containing a few isolated bundles, and are 

 ultimately blended with the capsule of the lens. From the ora serrata 

 to the commencement of the "canal of Petit," no hyaloid membrane 

 besides the fibres of the zonula, can be any longer distinguished, whilst 

 at the canal itself, where the substance of the vitreous body is separated 

 from the fibrous layer, it is again furnished with a limitary membrane, 

 only thinner than before, which constitutes the posterior wall of the 

 " canal of Petit," and extends no farther than to the border of the lens, 

 where it ceases as a special membrane, the vitreous body being most 

 intimately united with the posterior lamina of the capsule of the lens. 



M. Langenbeck, some years ago described, in the free portion of the 

 zonula Zinnii, what he believes to be a muscular ring, and terms the 

 musculus compressor lentis s. accommodatorius (" Klinisch. Beitrage zur 

 Ophthalmol.," 1849, p. (jQ), of which I have been unable to perceive any 

 indication. He has probably confounded the zonular fibres with such a 

 structure. 



B. ACCESSORY ORGANS. 



§ 230. The eyelids are supported by the so-termed tarsal cartilages 

 (tarsi), thin, semilunar, flexible, but tolerably elastic plates, attached 

 internally and externally by the fibrous, tarsal ligaments, — and belong- 

 ing, as far as their structure is concerned, to the solid, fascicular, con- 

 nective tissue, though occasionally containing a certain number of minute 

 cartilage cells. These plates, •3-0-4 of a line thick, the fibres in which 

 chiefly run parallel with the borders, are covered externally by the orbi- 

 cularis palpebrarum and the integuments, and internally by the con- 



