58 



THE EYE. 



THE VITREOUS BODY. 



The vitreous body occupies the greater portion 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 (fossa patellaris) for the 

 reception of the lens and its capsule, to which it is closely adherent. The vitreous 

 humour contains 98*5 % of water. The solids are chiefly salts and extractives, 

 with a trace of proteid and nucleoalbumin. 



The surface of the vitreous humour is covered everywhere by a thin glassy 

 membrane, named hyaloid, which lies between it and the retina. In the last edition 



Fig. 66. HORIZONTAL SECTION OF THE HORSE'S! EYE 

 HARDENED IN CHROMIC ACID (after Hannover). 



The vitreous humour appears concentrically and me- 

 ridionally striated throughout its whole depth. 



of this work it was stated that, according to 

 the most recent observations, there is no binding 

 membrane between the vitreous humour and the 

 lens capsule, but it has been shown by Anderson 

 Stuart that the older view regarding this subject 

 is more correct, for after removal of the lens 

 within its capsule it is still possible to demon- 

 strate the existence of a delicate glassy mem- 

 brane over the fossa patellaris in the front of the vitreous humour, and this can 

 be none other than a continuation of part of the hyaloid membrane. No 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 presenting under the 

 microscope but faint traces of fibres and a few cells the so-called corpuscles of the vitreous 



Fig. 67. TRANSVERSE SECTION OF HUMAN EYE HARDENED IN CHROMIC ACID, 

 SHOWING RADIAL STRIATION OF THE VITREOUS BODY (after Hannover). 



humour to which we shall immediately 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 in its peripheral part, that, namely, nearest 

 the retina ; which part in the human eye has a somewhat firmer 

 consistence than the more central portion. From the appearances 

 (figs. 66, 67) which have been obtained by such modes of preparation it has been conjectured 

 by various observers that at least in this part the vitreous substance is divided into com- 

 partments by a number of delicate membranes arranged concentrically and parallel to the 

 surface ; but the existence of such membranous partitions has not been conclusively 

 demonstrated. That, however, the vitreous substance does in some way consist of a firmer 

 material either in the shape of continuous membranes, or, as II. Virchow states, in the form 

 of a network of fibres 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. 



