. Quain's elements of anatomy . ording to the colour of the eye. At the posterior surfaceis a covering of dark pigment, the uvea of authors ; this is continuouswith the (retinal) pigmentary layer lining the ciliary processes, and hereconsists of several strata of small roundish cells filled with black pigment-granules. The colour of the iris depends on the pigment in the stroma-cells ; in the diiferent shades of blue eye it arises from the black pigmentof the posterior surface appearing moie or less through the stroma,which in such cases is only slightly coloured or is colourless ; but in theb
. Quain's elements of anatomy . ording to the colour of the eye. At the posterior surfaceis a covering of dark pigment, the uvea of authors ; this is continuouswith the (retinal) pigmentary layer lining the ciliary processes, and hereconsists of several strata of small roundish cells filled with black pigment-granules. The colour of the iris depends on the pigment in the stroma-cells ; in the diiferent shades of blue eye it arises from the black pigmentof the posterior surface appearing moie or less through the stroma,which in such cases is only slightly coloured or is colourless ; but in theblack, brown, and grey eye, the colour is due to the pigment-cellsscattered through the substance of the stroma itself. The muscular tissue is of the non-striated kind, and is disposed asa ring {s])hincter) around the pupil, and as rays {dilatator) from thesphincter to the circumference. The siMndsr (fig. 341, a) is a narroAV band about -j^ of an inchwide, situated close to the pupil posteriorly. Near the margin of the Fig. Fig. 341.—SEaMENT of the iris, SEEN FROM THE POSTERIOR SUR-FACE AFTER REMOVAL OP THEUVEAL PIGMENT (Iwanoff). a, sphincter nmscle ; h, dilatatormuscle of the pupil. pupil the j&bres are closetogether, but the outermostfibres are more separated,and form less completerings. The dilatator (b), lessapparent than the sphincter,begins at the ciliary or outer margin of the iris, and its fibres, forminga continuous membrane close to the posterior surface, converge towardsthe pupil. Here they bend round and blend with the sphincter, somereaching nearly to its inner margin. At their origin at the ciliarymargin, they also arch round and take a somewhat circular direction. Vessels of the iris.—The long ciliary arteries, two in number, jjiercethe sclerotic a little in advance, and one on each side, of the optic gained, the interval between the sclerotic and choroid coats,they extend horizontally forwards (figs. 337, 338, l, fig. 342, 1) coveredby loo
Size: 1956px × 1278px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., boo, bookcentury1800, booksubjectanatomy, booksubjecthumananatomy
