RETINA OR XERYOUS TUXIC. 725 



the choroid. They are somewhat flattened in form, are partly embedded in grooves 

 on the inner surface of the sclerotic, and communicate occasionally with each other 

 before supplying the cornea and entering the ciliary muscle. AY hen the sclerotic is 



Fig. 473. 



Fig. 473. DISTRIBUTION OP 

 NERVES IN THE IRIS (from 

 Kolliker). 5JL 



The preparation was taken from 

 the eye of an albino rabbit, and 

 Avas treated with soda, a, smaller 

 branches of the ciliary nerves ad- 

 vancing from the choroid ; 6, loops 

 of union between them at the mar- 

 gin of the iris ; c, arches of union 

 in the iris ; </, finer network in the 

 inner part; d, some of the termi- 

 nations of single nerve- filaments 

 in the outer part of the iris ; e, 

 sphincter pupillae muscle. 



carefully stripped from the subjacent structures, these nerves are seen lying on the 

 surface of the choroid. Within the ciliary muscle the nerves subdivide minutely, a few 

 being lost in its substance, but the greater number pass on to the iris. In the iris the 

 nerves follow the course of the blood-vessels, dividing into branches, which com- 

 municate with one another as far as the pupil. In the iris they soon lose their dark 

 outline, and their mode of termination is not ascertained. 



RETINA OR NERVOUS TUNIC. 



The retina is a delicate almost pulpy membrane, which contains the ter- 

 minal part of the optic nerve. It lies within the choroid coat, and rests on 

 the hyaloid membrane of the vitreous humour. It extends forwards nearly 

 to the outer edge of the ciliary processes of the choroid, where it ends in a 

 finely indented border or a serrata. From this border there is continued 



Fig. 474. THE POSTERIOR HALF OF THE Fig. 474. 



RETINA OP THE LEFT ETE VIEWED 

 FROM BEFORE (after Henle). f 



s, the cut edge of the sclerotic coat ; 

 ch, the choroid ; ?*, the retina : in the 

 interior at the middle the macula lutea 

 with the depression of the fovea centralis 

 is represented by a slight oval shade ; 

 towards the left side the light spot 

 indicates the colliculus or eminence at 

 the entrance of the optic nerve, from the 

 centre of which the arteria centralis is 

 seen spreading its branches into the 

 retina, leaving the part occupied by the 

 macula comparatively free. 



onwards a thin layer of transparent 



nucleated cells (not nerve-elements) 



of an elongated or cylindrical form, 



constituting the pars ciliaris retinae. 



which reaches as far as the tips of the ciliary processes, and there gradually 



disappears. The thickness of the retina diminishes from behind forwards. In 



the fresh eye it is translucent and of a light pink colour ; but after death it 



soon becomes opaque, and this change is most marked under the action of 



