580 BULBUS OCULI 



festooned border termed the ora serrata. This appearance, 

 however, is somewhat deceptive. The nerve elements, it 

 is true, come to an end along this line, but a lamina in 

 continuity with the retina is in reality prolonged antero- 

 medially as far as the margin of the pupil. The part in 

 relation to the ciliary processes is exceedingly thin, and 

 cannot be detected by the naked eye. It is termed the 

 pars ciliaris retina. The portion on the deep surface of the 

 iris is called the stratum pigmenti iridis. 



During life the retina proper is transparent, but after death 

 it soon assumes a dull greyish tint and becomes opaque. 

 Posteriorly it is tied down at the optic entrance. When 

 viewed from the anterior aspect this appears as a conspicuous 

 circular disc termed the papilla nervi optici, upon which is 

 a depression, the excavatio papilla. From this spot the 

 optic nerve fibres radiate out so as to form the deep or 

 anterior layer of the retina. The optic disc, in correspond- 

 ence with the entrance of the optic nerve, lies to the medial 

 or nasal side of the antero -posterior axis of the eyeball. 

 Exactly in the centre of the human retina, and therefore in 

 the axis of the globe of the eye, there is a small yellowish 

 spot termed the macula lutea. 1 It is somewhat oval in 

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

 centralis. 



Retinal Arteries and Veins. In a fresh eyeball the 

 arteria centralis retince, will be seen entering the retina at 

 the optic disc. It immediately divides into a superior 

 and an inferior branch, and each of these breaks up 

 into a large lateral or temporal division, and a smaller 

 medial or nasal division. These ramify in the retina as far as 

 the ora serrata ; but the resultant branches 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 is produced by the blood in the lamina 

 chorio-capillaris. 



1 There is no macula lutea in the eyeball of the ox or sheep. 



