. Cunningham's Text-book of anatomy. Anatomy. Retina Fig. -A Segment of the Bdlbus Oculi showing the Oka Serrata. the retina appears to end, a short distance behind the ciliary body, in a wavy border, the ora serrata (Fig. 686). Here its nervous elements cease and the mem- brane becomes suddenly thinned, but a delicate continuation of it is prolonged over the posterior aspect of the ciliary body and iris. This continuation consists of the pig- mented layer, together with a layer of columnar epithelium, and con- stitutes the pars ciliaris retinae and pars iridica retinae, already referred
. Cunningham's Text-book of anatomy. Anatomy. Retina Fig. -A Segment of the Bdlbus Oculi showing the Oka Serrata. the retina appears to end, a short distance behind the ciliary body, in a wavy border, the ora serrata (Fig. 686). Here its nervous elements cease and the mem- brane becomes suddenly thinned, but a delicate continuation of it is prolonged over the posterior aspect of the ciliary body and iris. This continuation consists of the pig- mented layer, together with a layer of columnar epithelium, and con- stitutes the pars ciliaris retinae and pars iridica retinae, already referred to (p. 813). The portion behind the ora serrata is termed the pars optica retinae, and its thickness gradually diminishes from 0-4 mm. near the entrance of the optic nerve, to 01 mm. at the ora serrata. It presents, at the posterior pole of the eye, and therefore directly in the optic axis, a small, oval yellowish spot, the macula lutea. The greatest or transverse diameter of the macula measures from 2-3 mm.; its central part is depressed and is named the fovea centralis. About 3 mm. to the nasal side and slightly below the level of the posterior pole is a whitish, circular disc, the optic disc, which corresponds with the entrance of the optic nerve, and has a diameter of about 1*5 mm. The circum- ference of the optic disc is slightly raised and is named the papilla nervi optici, while its depressed central portion is termed the excavatio papillae nervi optici ( optic cup). The optic disc consists merely of nerve-fibres, the other layers of the retina being absent, and it constitutes the " blind ; The nervous layer of the retina is transparent during life, but becomes opaque and of a grayish colour soon after death. If an animal is kept in the dark before the removal of its eyeball, the retina presents a purple tinge, due to the presence of a colouring matter named rhodopsin or visual purple, which is rapidly bleached on exposure to sunlight. This colouring
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1914
