. Compendium of histology. Histology. 250 TWENTY-FOURTH LECTURE. boundary region of the cornea and sclerotica. Meridional bundles of the former radiate in a posterior direction into the ciliary body. Below and inwards occur interwoven filaments, and still further inwards, circular bundles (Mueller's ring muscle). We meet with colorless connective-tissue cells in the con- nective-tissue substratum of the iris of light eyes, and pig- mented cells in that of dark ones. Besides these, smooth muscular elements occur. Annular bundles (Fig. 201, a). Fig. 201. —Surface of the human iris ; a, the sphin
. Compendium of histology. Histology. 250 TWENTY-FOURTH LECTURE. boundary region of the cornea and sclerotica. Meridional bundles of the former radiate in a posterior direction into the ciliary body. Below and inwards occur interwoven filaments, and still further inwards, circular bundles (Mueller's ring muscle). We meet with colorless connective-tissue cells in the con- nective-tissue substratum of the iris of light eyes, and pig- mented cells in that of dark ones. Besides these, smooth muscular elements occur. Annular bundles (Fig. 201, a). Fig. 201. —Surface of the human iris ; a, the sphincter ; b, the dilator of the pupil. form the constrictor or sphincter of the pupil. From it pro- ceeds the dilator pupillse, an object of controversy of later years. Muscular bundles, which are at first separated, form more peripherically a connected radial layer of fibres (b). At the ciliary, that is the outer border, we finally meet with an an- nular muscular layer. This external or ciliary border of the iris gives rise at its anterior surface to another peculiar tissue, the ligamentum pectinatum iridis (Huek). We have already learned (p. 56) that the posterior surface of the cornea is covered by a hyaline membrane, the mem- brana Descemetica or Demoursii. At its periphery, this posterior covering layer passes over into a peculiar reticular tissue (probably, in man, most intimately connected with the elastic tissue), which passes through the outer margin of the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Frey, Heinrich, 1822-1890; Cutter, George R. (George Rogers), b. 1840, tr. New York, G. P. Putnams sons
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