The development of the human body; a manual of human embryology . ion of which to the thickerretinal portion of the layer is somewhat abrupt and corre-sponds to what is termed the ora serrata in adult embryos of cm. the retinal layer throughout itsentire extent is readily distinguishable from the pigmentlayer by the absence in it of all pigmentation, but in olderforms this distinction gradually diminishes in the iris re-gion, the retinal layer there acquiring pigment and form-ing the uvea. When the anterior chamber of the eye is formed by thesplitting of the mesoderm which has
The development of the human body; a manual of human embryology . ion of which to the thickerretinal portion of the layer is somewhat abrupt and corre-sponds to what is termed the ora serrata in adult embryos of cm. the retinal layer throughout itsentire extent is readily distinguishable from the pigmentlayer by the absence in it of all pigmentation, but in olderforms this distinction gradually diminishes in the iris re-gion, the retinal layer there acquiring pigment and form-ing the uvea. When the anterior chamber of the eye is formed by thesplitting of the mesoderm which has grown in between thesuperficial ectoderm and the outer surface of the lens, the THE IRIS AND CILIARY BODY. 48S peripheral portions of its posterior (inner) wall are in rela-tion with the ciliary portion of the optic cup and give riseto the stroma of the ciliary body and of the iris (Fig. 257)this latter being continuous with the tunica vasculosalentis so long as that structure persists (Fig. 264). Inembryos of about cm. the ciliary portion of the cup Fig. 257.—Radial Section through the Iris of an Embryo op 19 , Pigment layer; CC, ciliary folds; IE, retinal layer; , irisstroma; Pm, pupillary membrane; Rs, marginal sinus; Sph, sphinc-ter iridis.—(Szili.) becomes thrown into radiating folds (Fig. 257), as if by atoo rapid growth, and into the folds lamella? of mesodermproject from the stroma. These folds occur not onlythroughout the region of the ciliary body, but also extendinto the iris region, where, however, they are but tem-porary structures, disappearing entirely by the end of the 486 THE DEVELOPMENT OF THE HUMAN BODY. fifth month. The folds in the region of the corpus ciliarepersist and produce the ciliary processes of the adult eye. Embedded in the substance of the iris stroma in theadult are non-striped muscle-fibers, which constitute thesphincter and dilatator iridis. It has long been supposedthat these fibers were differentiated from the strom
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
