THE VITKEOUS BODY. 



610 



THE VITREOUS BODY. 



The vitreous body, the largest of the transparent parts through which 

 the light passes to reach the retina, occupies the centre of the eyeball. 

 It is quite pellucid in aspect, and of a soft gelatinous consistence. Sub- 

 globular in form, it fills about four-fifths of the ball, and serves as a 

 support for the delicate retina, but it may be readily separated from the 

 latter, except behind, at the entrance of the optic nerve, ■where the 

 connection is closer, the retinal vessels having here entered it in 

 foetal life. At the fore part it is hollowed out for the reception of the 

 lens and its capsule, to which its substance is closely adherent. 



The surface of the vitreous humour is covered everywhere except in 

 front by a thin glassy membrane, named lujaloid, which lies between 

 it and the retina. Ko vessels enter the vitreous humour in the adult, 

 and its nutrition must, therefore, be dependent on the surrounding 

 vascular structures, viz., the retina and the ciliary processes. 



Although in the fresh state apparently structureless, or at least pre- 

 senting under the microscope but faint traces of structural elements — 

 the so-called corpuscles of the vitreous humour to Avhich we shall im- 

 mediately recur, — yet in preparations hardened in weak chromic acid, or 

 acted upon in certain other ways, it is possible to make out a more or 

 less distinct lamellation of the vitreous body, especially its peripheral 

 part, that, namel}', nearest the 



retina, which part in the human Fig- 429. 



eye has a somewhat firmer con- 

 sistence than the more central 

 portion. From the appearances 

 (fig. 429) which have been 

 obtained with such modes of 

 preparation it has been con- 

 jectured by various observers 

 that at least in this part the 

 vitreous substance is divided 

 into enclosed, flattened compart- 

 ments by a number of exces- 

 sively delicate membranes ar- 

 ranged concentrically and there- 

 fore parallel to the surface, but the 

 existence of such membranous 

 partitions has not been con- 

 clusively demonstrated. That, 

 however, the vitreous substance 

 does in some way consist of a 

 firmer material — whether or not 

 in the shape of continuous membranes — enclosing in its meshes 

 the more fluid portion, is shown by the fact that if either the whole or a 

 piece of the vitreous humour be thrown upon a filter, a small proportion 

 always remains upon the latter ; although by far the larger part drains 

 away, and may be collected as a clear watery fluid. 



In addition to the above-mentioned concentric striation, a radial 

 marking has also been observed in sections of the human vitreous 



Fig. 429. — Horizontal Section of the 

 Horse's Eye, hardened in Chromic 

 Acid (after Hannover). 



The vitreous humour appears concentric- 

 ally and meridionally striated throughout its 

 whole depth. 



