EXAMrXATfOX OF THE EYEBALL 845 



is of a lipVit browniish coldur, mainly in»iu tlie presence of a delicate piffuieiited layer, tlic mem- 

 brana suprachoroidea, wiiieli adlieies jmrtly to it, partly to the choroid, giving to their adjacent 

 surface.^ a fl(tcculent appearance when examined under water. 



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

 the middle, with the large clear crystalline lens lying behind it. The retina proper extends 

 forwards a little way from our line of .section, and then ends abruptly in a wavy line called the ora 

 serrata, beyond which it is only re|iresented by a very thin m(nd)rane (pars ciliaris retinae). 

 Outside the periphery of the lens are a number of ciliary processes arrangeil closely together 

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

 with numerous fine Iblds, also radial, which ."^oon get vi'ry indistinct as they pa.-^s bac-kwards, hut 

 reach almost to the ora serrata (plicae ciliares). Between the front ol' the ciliary i)roeesses and 

 the edge of the iiupil lies the iris. On removal of the retina the inner surface of all this regi(jn 

 is seen to be darkly pigmcjnted, but especially dark in front of the positi(jn of tiie ora serrata. 

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

 removed along with its capsule and suspensory ligament ; some jiigincnt will now be iifund 

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

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

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

 posterior surfaces of the lens. The suspensory ligament is a transi>arent membiane attached to 

 the cajisule of the lens about its eijuator, and is bi-st seen by floating the lens in water in a gla.ss 

 vessel jilaced on a dark ground. On oiiening the cajisule we expose the lens itself which is 

 supeifi -ially .soft and glutinous to the tcnich, but Ix'comes firmer as we rub off its outer layers and 

 approach its centre. Carefully tear the choroid and iris from the sclerotic : a firm adhesion exists 

 just behind the corneal iieriphery. Their outer surface thus exposed is found to be also rather 

 darkly pigmented (as far forward as the base of the iris at least), but it shows a white ring corre- 

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

 of the ciliary muscle. On this surface numerous white nerve-cords are visible running forwards. 



Fig. 475. — Equatorial Section' of Eyeball : Anterior Segment viewed from 



BEHIND. (After Merkel. ) 



PUPIL 

 CILIARY PROCESSES 



PLIC/t CILIARES 



Observe that the iris, the ciliary processes, etc., and the choroid are all different i)arts of the 

 same ocular tunic — mere local modifications of it. Similarly the sclerotic and cornea are seen to 

 blend together to form one outer coat. 



An eyeball should now be placed for half an hour in a freezing mixture of crushed ice and 

 salt. It will thus become (|uite hard, and should at once be divided into two jiarts by cutting it 

 antero-posteriorly through the centre of the cornea and the optic nerve. We thus gain another 

 view of the relations of parts, the position of the lens between the aqueous and vitreous chambers, 

 etc. On removing the lens, vitreous, and retina, and brushing oft' its pigment, the light mark- 

 ings corresponding to the choroidal veins (venae vorticosae") should be noted, and their distri- 

 bution studieil. Usually four vortices or fountain-like markings are found in the whole choroid, 

 their points of junction situated at aiiproximatcly e(|ual distances from one another at about the 

 line where the posterior and middle thirds of the globe meet. These sections should be kept for 

 reference while following the further description of the ocular tunics. 



1. The outer, fibrous coat of the eye is foniud by fhe sclerotic an<l corncn. 

 wliich pass into one another at the scleral sulcus. It c(jnsists throughout mainly 

 of fine coiuiective-tissue filjres, arranged in intcrlaeintr bundles, with small lympli- 

 s|)aces at intervals between them. The naked-eye a})])earance of the two divisions 

 of this fibrous coat is, however, (|uite difTerent, the cornea heinj; trans|iar<nt, while 

 the sclerotic is white and opacjue. 



The sclerotic encloses the posterior five-sixths or so of tlie eyeball, but there is 

 a hole in it at the entrance of tlie optic nerve (foramen sclerae), only partially 

 bridged .across by fibres from its inner layers forming the lamina cribrosa. The 

 fibre-bundles composing the sclerotic are arranged more irregularly thati in the 

 cornea, and run mainly in two directions, viz. from before backwards, and 

 circularly; the circular fibres are particularly well developeil just behind the 

 sulcus. It is thickest (about 1 mm.) posteriorly, where it is strengthened chiefly 



