800 



DISSECTION OF THE EYE. 



Artery of 

 retina 



has four 

 chief 



branches ; 



another in 

 foetus. 



Vitreous 

 body. 



To obtain i 



view of it, 



and of its 

 front. 



Form and 

 position of 

 vitreous : 



it consists 

 of jelly, 



with a 

 central 

 canal ; 



and of the 



hyaloid 



membrane 



both are 

 without 

 vessels. 



Suspensory 

 ligament : 



retina, but does not consist of nervous substance. It is not visible 

 to the naked eye. 



For a description of the structure of the retina, the student is 

 referred to a work dealing with microscopic anatomy. 



Vessels of the retina. The central artery of the retina, accom- 

 panied by its veins, enters the eyeball through the optic nerve. In 

 the central depression of the optic papilla the artery divides into. 

 four primary branches, two inner or nasal (upper and lower), and 

 two outer or temporal (also upper and lower). The outer branches 

 are the larger, and follow an arched coarse above and below the 

 yellow spot : all ramify in the innermost part of the nervous coat. 

 No vessels enter the pigmentary layer. The veins have a similar 

 arrangement. 



In the foatus a branch of the artery passes through the centre of 

 the vitreous mass to supply the lens-capsule. 



VITREOUS BODY. This is a soft transparent mass which fills the 



greater part of the space within the coats of the eyeball (fig. 288, h), 



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 eyeball should be fixed upright, and the sclerotic and choroid 

 coats cut through about a quarter of an inch behind the cornea ; 

 then on removing carefully the cornea, the ciliary muscle and pro- 

 cesses, and the iris, the vitreous body will be apparent. 



The vitreous body (fig. 288, h) is globular in form, and fills about 

 four-fifths of the ball, supporting the retina. In front it is slightly 

 hollowed, and receives the lens (</), with its capsule to which it is 

 closely united. It is composed of a thin watery jelly, contained 

 in a transparent membrane named hyaloid. The jelly consists in 

 great part of fluid, which drains away when the vitreous body is 

 exposed on a flat surface, or placed 011 a filter, and only a very 

 small amount of solid matter remains. In the central part of the 

 vitreous body, however, there is a canal filled with fluid (hyaloid 

 canal), which extends from the optic papilla of the retina to the 

 back of the lens-capsule, and served in the foetus for the trans- 

 mission of the capsular branch of the central artery of the retina : 

 but this canal is not visible without special preparation. 



The hyaloid membrane (ri) is the thin, glassy, structureless layer 

 enclosing the vitreous body, except at the fore part where the lens 

 is placed. At the bottom of the ball, around the optic papilla, the 

 membrane is closely connected with the retina ; and it sends a 

 prolongation forwards to line the canal of the vitreous. In front, 

 the membrane becomes thicker as it approaches the ciliary processes, 

 and is continued into the suspensory ligament of the lens. 



The vitreous mass and the hyaloid membrane are extravascular, 

 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 transparent membranous structure (fig. 291, ), placed around 



