VITREOUS BODY AND MEMBRANE. 



667 



fluid, contained in a translucent membrane, and has the consistency of 

 jelly. 



Dissection. The vitreous body may be seen on the eye on which the 

 retina was dissected, by taking away the retina, the iris, and the ciliary 

 muscle and processes. 



To obtain a view of its anterior part, with the lens in situation, an eye- 

 ball should be fixed upright ; the sclerotic and choroid coats are to be cut 

 through about a quarter of an inch behind the cornea ; and on removing 

 carefully the cornea, ciliary muscle, and processes with the iris, the vitre- 

 ous body will be apparent. 



The vitreous body (fig. 227, h) is globular in form, and fills four-fifths 

 of the ball, supporting the retina. In front it is slightly hollowed, and 

 receives the lens with its capsule (.17), to which it is closely united. The 

 fluid of the vitreous body has nearly the same composition as the aqueous 

 humor with some salts and albumen. Enveloping the whole is a thin 

 membrane named hyaloid. 



The hyaloid membrane (11) is a fine transparent covering of the vitreous 

 body. It passes continuously over the surface ; and in the foetus it is 

 connected with fibres which penetrate the mass. On the inner aspect are 

 a few delicate nuclei. 



At the fore part it is joined by the membrane (t) supporting the lens; 

 and it ends by uniting with the back of the lens capsule. At the bottom 

 of the ball the membrane is closely connected with the retina. 



Structure of the vitreous mass. From the slow escape of the fluid after 

 puncture of the hyaloid membrane, it has been supposed that there are 

 membranous partitions, dividing the vitreous mass into compartments 

 which communicate with each other. In the centre of the vitreous body 

 is a fibrous canal, which reaches to the back of the lens, and transmits a 

 branch from the central artery of the retina to the lens capsule in the 

 foetus. 



The vitreous mass and the hyaloid membrane are extra-vascular, and 

 receive their nutritive material from the vessels of the ciliary processes 

 and retina. 



Suspensory ligament of the lens (Zonule of Zinn). This is a transpa- 

 rent membranous structure (fig. 285, ), placed around the lens capsule, 



Fig. 235. 



d. Cornea. 



e. Ciliary muscle. 

 /. Iris. 



g. Lens. 



i. Posterior chamber. 

 j. Ciliary part of the retina. 

 in. Ciliary ligament. 

 n. Hyaloid membrane. 

 o. Canal of Petit. 

 r. Sinus circularis iridis. 

 s. Ciliary process. 

 t. Suspensory ligament of the lens. 

 ENLAROKD REPRESENTATION OF THE PARTS OF THE EYEBALL ON ONE SIDE OPPOSITE THE LENS : 

 THE LETTERS REFER TO THE SAMK PARTS AS IN THE WOODCUT, 227. 



which joins externally the hyaloid membrane opposite the anterior termi- 

 nation (ora serrala) of the retina. After the ciliary processes of the cho- 

 roid coat are detached from it, dark lines of pigment cover the surface ; 



