Text-book of ophthalmology . LMOLOGY perception. And so when we wish to get a precise perception of an object,we so adjust our eye that the image shall fall upon the fovea; we [sightwor] fix the object. 510. Pigment Epithelium.—The membrane here described—the retina,in the narrower sense of the word—develops from the inner layer of the sec-ondary ophthalmic vesicle (page 390 and Fig. 161, r). From the outer layerof the vesicle (p, Fig. 161) is developed the pigment epithelium, which there-fore must, on embryological grounds, be counted in with the retina (in thewider sense of the term). It lie
Text-book of ophthalmology . LMOLOGY perception. And so when we wish to get a precise perception of an object,we so adjust our eye that the image shall fall upon the fovea; we [sightwor] fix the object. 510. Pigment Epithelium.—The membrane here described—the retina,in the narrower sense of the word—develops from the inner layer of the sec-ondary ophthalmic vesicle (page 390 and Fig. 161, r). From the outer layerof the vesicle (p, Fig. 161) is developed the pigment epithelium, which there-fore must, on embryological grounds, be counted in with the retina (in thewider sense of the term). It lies upon the chorioid along the outer side ofthe retina, and, because it remains behind when the retina is removed fromthe chorioid, was formerly regarded as belonging to the latter. The con-nection between the retina and pigment epithelium consists in the fact thatthe cells of the latter send minute cilia-like processes in between the rodsand cones; in these processes lie the minute crystals of the brown [Fig. 245.—Section of Human Retina at the Ora Serrata. (After Piersol in Norris and Oliver.)Shows the abrupt termination of the usual retinal layers and the continuation of the retinalsheet as the pars ciliaris.—a, pigment layer; b, rods and cones; c, outer nuclear layer; d, outer plexi-form; e, inner nuclear; /.inner plexiform; g, ganglion cells; h, point of transition into inner stratum(k) of pars ciliaris; i, section of cyst. Magnified 165 diameters.—D.] 511. Continuation on Ciliary Body and Iris.—The cessation of theretina at the ora serrata is apparent only; the microscope shows that undera simpler form it extends still farther, even up to the edge of the pupil. Ittherefore lines the inner surface of the ciliary body and the posterior surfaceof the iris. The portion of the retina lying upon the ciliary body is calledthe pars ciliaris retince [Fig. 142, pe and pc\. Wherever this extends, theexternal layer of the retina, or pigment epithelium (F
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