542 BULBUS OCULI 



exposing the ciliary processes from the posterior aspect, should 

 now be dislodged. By raising the chorioid coat from the deep 

 surface of the sclera, under a flow of water from the tap, the 

 dissector will bring into view the venae vorticosae as they enter 

 the deep surface of the sclera. When the venae vorticosae are 

 divided, and the separation of the two coats is carried backwards 

 towards the optic entrance, the short posterior ciliary arteries, 

 as they emerge from the sclera and enter the posterior part of 

 the chorioid, will be seen. 



To expose the external surface of the retina take the eyeball 

 from which the sclera and cornea have been removed, and care- 

 fully strip off the iris, ciliary processes, and the chorioid, piece- 

 meal, under water. 



Eetina. The retina is composed of two strata viz., a 

 thin pigmentary layer^ which adheres to the deep surface of 

 the chorioid coat, and has been removed with it, and a 

 delicate nervous layer^ which is moulded on the surface of 

 the vitreous body, but presents no attachment to it except at 

 the optic entrance. The retina extends forwards, beyond 

 the equator of the eyeball, and, a short distance from the 

 ciliary zone, it appears to end in a well-defined, wavy or 

 festooned border termed the ora serrata. This appearance, 

 however, is somewhat deceptive. The nerve elements, it 

 is true, come to an end along the ora serrata, but a lamina in 

 continuity with the retina is in reality prolonged forwards 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 the optic entrance appears as 

 a conspicuous circular disc termed fae papilla nervi optici, upon 

 which is a depression, the excavatio papilla. From that 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 



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



