THE EYEBALL 1057 



posteriores breves] are too small to be seen in an ordinary examination. The 

 nerves are the long and short ciliary [nn. ciliares longi, breves]. Nearer the equator 

 large venous trunks emerge; they can be traced for some distance in front of their 

 exit as dark lines, running antero-posteriorly internal to the sclera. The optic 

 nerve is seen in section, surrounded loosely by a thick outer sheath; in the centre of 

 the nerve-section a small red spot indicates the position of the central retinal 

 blood-vessels [a. et v. centralis retinae]. 



(The following structures appear in an eyeball divided into fore and hind halves by cutting 

 thi'ough it in the equatorial plane.) 



1. Posterior hemisphere seen from in front. — This is much the same view that the ophthal- 

 moscope affords us. Unless the eye be very fresh, however, the retina will have lost its trans- 

 parency, and will now present the appearance of a thin whitish membrane, detached in folds 

 from the external coats, but still adherent at the optic papilla. The vitreous jelly lying within 

 the retinal cup may be torn away. In the human eye the retina next the posterior pole is stained 

 yellow [macula lutea]. On turning the retina over, a little pigment may be seen adhering to 

 its outer surface here and there. Cut through the retina close to the optic disc all around and 

 remove it: note how easily it is torn. We now see a dark brown surface, consisting of the 

 retinal pigment layer [stratum pigmenti retina^] adherent to the inner surface of the chorioid. 

 Brush off the retinal pigment under water. The chorioid thus exposed can for the most part 

 be fairly easily torn away from the thick sclera, as a lymph-space exists between them, but the 

 attachment is firm around the optic nerve entrance, and also where the arteries and nerves join 

 the chorioid after penetrating the sclera. The chorioid is darkly pigmented, of a brown colour, 

 with markings on its surfaces corresponding to the distribution of its large veins. The inner 



Fig. 801. — Anterior Hemisphere of Eyeball, Viewed from Behind. 



Pupil 



Ciliary processes 



Orbiculus ciliaris 



surface of the sclera is of a light brownish colour, mainly from the presence of a delicate pig- 

 mented layer, the lamina suprachorioidea, which adheres partly to it, partly to the chorioid, 

 giving to their adjacent surfaces a fiocculent appearance when examined under water. 



2. Anterior hemisphere viewed from behind. — The round opening of the pupil is visible in 

 the middle, in front of the large clear crystalline lens. The retina proper extends forward a 

 little way from the line of section, and then ends abruptly in a wavy line called the era serrata, 

 beyond which it is only represented by a very thin membrane [pars ciliaris retinae]. Outside 

 the periphery of the lens are a number of ciliary processes arranged closely together in a circle 

 concentric with the pupil, and each radially elongated; posteriorly they are continuous with 

 n umerous fine folds, also radial, which soon get very indistinct as they pass backward, but 

 readh almost to the ora serrata [plicae ciliares]. Between the front of the ciliary processes and 

 the edge of the pupil lies the iris. On removal of the retina the inner surface of all this region 

 is seen to be darkly pigmented, but especially dark in front of the position of the ora serrata. 

 Vitreous probably still adheres to the back of the lens, and by pulling upon it the lens can be 

 removed along with its capsule and suspensory ligament ; some pigment will now be found 

 adhering to the front of the vitreous, torn from the ciliary processes, which are consequently 

 now lighter in colour than before. The lens-capsule is transparent, and has a smooth glistening 

 outer surface; through it a greyish, star-shaped figure may be observed on the anterior and 

 posterior surfaces of the lens. The suspensory ligament is a transparent membrane attached to 

 the capsule of the lens about its equator, and is best seen by floating the lens in water in a glass 

 vessel placed on a dark ground. On opening the capsule we expose the lens itself, which is 

 superficially soft and glutinous to the touch, but becomes firmer as we rub off its outer layers and 

 approach its centre. Carefully tear the chorioid and iris from the sclerotic as far as possible; 

 a firm adhesion exists just behind the corneal periphery. The outer surface of the chorioid 

 thus exposed is found to be also rather darkly pigmented, but it shows a white ring corresponding 

 to the adhesion just mentioned, and a pale area behind this ring indicates the position of 

 the ciliary muscle [m. ciUaris]. On this surface numerous white nerve-cords are visible running 



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