RETINAL ARTERIES AND VEINS 543 



outline, and a depression in its centre is called the fovea 

 centralis. 



Retinal Arteries and Veins. In a fresh eyeball the 

 arteria centralis retina will be seen entering the retina at 

 the optic disc. 1 It immediately divides into a superior and 

 an inferior division, and each of them breaks up into a large 

 lateral or temporal division, and a smaller medial or nasal 

 division. The various branches of the terminal divisions 

 ramify in the retina as far as the ora serrata ; but they do not 

 anastomose with each other, nor with any of the other arteries 

 in the eyeball. 



' The retinal veins converge upon the optic disc, and 

 disappear into the substance of the optic nerve in the form 

 of two small trunks which soon unite. 



The retinal vessels, the optic disc, and the macula can all be examined 

 in the living eye by means of the ophthalmoscope. The red reflex obtained 

 from the fundus of the eyeball, so examined, is produced by the blood 

 in the lamina chorio-capillaris. 



Dissection. For the study of the vitreous body and the 

 crystalline lens, which together may be termed the " eye-kernel," 

 it is better to take an eyeball which is not perfectly fresh 

 (Anderson Stuart). The eyeball selected for this purpose should 

 be allowed to stand untouched from one to three days, according 

 to the season. Divide the coats of the eye round the equator ; 

 gently separate the cut edges, and turn the coats forwards and 

 backwards, and the " eye-kernel " will slip out. It should be 

 allowed to drop into a vessel filled with clean water. The 

 examination of the parts forming the " eye-kernel " will be 

 greatly facilitated if it is placed en masse in strong picro-carmine 

 solution for a few minutes. When removed from the staining 

 fluid, it should be well washed in water. In this way the hyaloid 

 membrane enclosing the vitreous body, the capsule of the lens, 

 and the zonula ciliaris, are stained red, and their connections 

 become very apparent (Anderson Stuart). 



Corpus Vitreum. The vitreous body is a soft, yielding, 

 transparent, jelly-like body, which occupies the posterior four- 

 fifths of the interior of the eyeball. The retina is spread 

 over its surface as far forwards as the ora serrata, but is in 

 no way attached to it, except at the optic disc. Anterior to 

 the ora serrata, the ciliary processes are applied to the 

 vitreous body and indent its surface. More anteriorly, the 

 vitreous body presents a deep concavity, called the fossa 



1 When the living retina is examined with the aid of the ophthalmoscope 

 it is not the vessels which are seen but the blood circulating through them, 

 for the walls of the vessels are transparent. 



