THE VITREO US BODY 1 1 07 



lace with those of the cells of the inner nuclear layer, while in the outer molecular layer a like 

 synapsis occurs between the processes of the inner granules and the rod and cone elements. 

 " The arteria centralis retinae (Fig. 802) and its accompanying vein, vena centralis retinae, 

 pierce the optic nerve, and enter the globe of the eye through the porus opticus. They bifurcate 

 on the surface of the papilla or just beneath it into an upper and a lower branch, and each of 

 these again divides into an inner or nasal, and an outer or temporal branch; these at first run 

 between the hyaloid membrane and the nerve layer; but they soon enter the latter, and pass 

 forward, dividing dichotomously. From these branches a minute capillary plexus is given off, 

 which does not extend beyond the inner nuclear layer. The macula receives small twigs from 

 the temporal branches and others directly from the central artery; these do not, however, reach 

 as far as the fovea centralis, which has no bloodvessels. The branches of the arteria ce.ntralis 

 retinae do not anastomose with each other in other words, they are "terminal arteries." In 

 the fetus, a small vessel passes forward, through the hyaloid canal in the vitreous body, to the 

 posterior surface of the capsule of the lens (Fig. 797). 



THE REFRACTING MEDIA. 



The Refracting media are three viz.: 



Aqueous humor. Vitreous body. Crystalline lens. 



I. The Aqueous Humor (Humor Aqueus). 



The aqueous humor completely fills the lymph space known as the aqueous 

 chamber, the space which is bounded in front by the cornea and behind by the 

 lens and its suspensory ligament and the ciliary body (Fig. 820). The aqueous 

 chamber is partly divided by the iris into two 

 communicating parts, the anterior and posterior 

 chambers (Figs. 797 and 820). The posterior 

 chamber (camera oculi posterior) is only a narrow 

 chink between the peripheral part of the iris, the 

 suspensory ligament of the lens, and the ciliary 

 processes. The anterior chamber (camera oculi 

 anterior] is bounded in front by the cornea and VITPEOUS, 

 behind by the iris. The external angle of the 

 anterior chamber is bounded by the periphery of FIG sis. The vitreous body re- 



. i i i T moved from the eye in the fresh state, 



the cornea and or the iris. It is called the angle with the saucer-shaped hollow in which 



,i -,. .. . f , 7- \ TJ i tne lens lies. Seen obliquely from the 



or the filtration angle (angiUus iridis). It is by way side and before. (Toidt.) 



of the filtration angle that any excess of aqueous 



humor passes by way of the spaces of Fontana and the canal of Schlemm (Fig. 



806) to the anterior ciliary veins and relieves tension. The aqueous humor 



is small in quantity, has an alkaline reaction, in composition is little more than 



water, less than 2 per cent, of its weight being solid matter, chiefly sodium chloride. 



II. The Vitreous Body (Corpus Vitreum) (Figs. 797, 817). 



The vitreous body occupies about four-fifths of the entire globe. It is composed 

 of a jelly-like tissue containing 98 per cent, water, some salts, and a little albumin, 

 and called the vitreous humor (humor vitreus], connective-tissue fibres, and con- 

 nective-tissue cells. It fills the concavity of the retina, and is hollowed in front, 

 forming a deep concavity, fossa hyaloidea (Fig. 815), for the reception of the lens. 

 It is perfectly transparent, of the consistence of thin jelly, and is composed of an 

 albuminous fluid enclosed in a delicate transparent membrane, the hyaloid mem- 

 brane (membrana hyaloidea), the outside of which is in contact with the memhrana 

 limitans interna of the retina. In the fetus a peculiar fibrous texture pervades 

 the mass, the fibres joining at the numerous points, and presenting minute nuclear 



