THE VITREOUS BODY. 



59 



In addition to the above-mentioned concentric striation, a radial marking has also been 

 observed in sections of vitreous humour made transversely to the axis of the eyeball, 

 but whether there is any pre-existent structure to account for it is not known. It is con- 

 ceivable that these appearances may be merely produced by the manner in which the 

 albuminous substance has undergone coagulation by the reagent employed. 



It has also been shown by Iwanhoff. Younan and A. Stuart that the periphery of the 

 vitreous humour near the ciliary body, is considerably strengthened and rendered more consistent 

 by the presence of an accumulation of fibres which encircle this part of the posterior chamber 

 of the eye, and are believed to aid in supporting the ciliary body and the attachment of the 

 suspensory ligament of the lens to that body. The fibrous structure in question appears to 

 be continuous with the fibres of the zonula of Zinn (see below), which here strengthen the 

 hyaloid membrane. 



There further exists, nearly but not quite in the axis of the eye, a definite 

 structure in the shape of a distinct canal, about 2 mm. in diameter, filled 

 with fluid and extending from the papilla optici to the back of the lens-capsule, 

 where it apparently terminates blindly (fig. 69). This is the canalis hyaloideus or 

 canal of Stilling. It is best shown in the fresh eye, and may be also injected by 

 forcing a coloured solution under the pia-matral sheath of the optic nerve (Schwalbe). 

 The canal widens somewhat towards its posterior part ; its wall is composed of an 

 extremely delicate homogeneous membrane. It represents the place of passage 

 of an offset from the central artery of the retina to the capsule of the lens in the 

 foetus, and from it lymph may pass into the lymphatic spaces of the optic nerve 

 behind, and perhaps in front round the edge of the lens into the canal of Petit. 



Fig. 68. CELLS OF VITREOUS HUMOURS. 



(Schwalbe.) 



a and d, without vacuoles ; b, c, e, f, g, 

 vacuolated. 



Scattered about throughout the sub- 

 stance of the vitreous humour are a 

 variable number of corpuscles, for the 

 most part possessed of amoeboid move- 

 ment. Some of these cellsare remarkable 

 for the very large vacuoles which they 

 contain, and which distend the. body 

 of the corpuscle, pushing the nucleus 

 to one side ; the cell-processes are often 

 peculiar in possessing numerous little 



secondary bud-like swellings, or they may present a varicose appearance, like strings 

 of pearls. 



Suspensory apparatus of the lens. The hyaloid membrane invests, as 

 before mentioned, the whole of the vitreous humour. As the ora serrata it is 

 apparently split into two layers, one, which must be regarded as the hyaloid 

 membrane proper, being that which has been already mentioned as demonstrable 

 over the anterior surface of the vitreous humour. The other layer into which the 

 hyaloid appears to split adheres to the pars ciliaris retina so closely that when 

 removed it generally shows some of the pigmented cells of that structure adher- 

 ing to its outer surface. It forms a fibrous structure much firmer in consistence 

 than the true hyaloid, and extends over the ciliary body inwards to be attached 

 to the capsule of the lens, for which it forms a suspensory apparatus, known as 

 the zonula of Zinn, or zonula ciliaris (fig. 70, z). Its free part, which stretches 

 from the ciliary body to the lens capsule, is termed the suspensory ligament of 

 the lens. The posterior part, or hyaloid proper, is exceedingly thin and delicate, 

 and is readily thrown into folds when detached. Under the microscope it presents no 



