. An American text-book of obstetrics. For practitioners and students. o (Piersol): B,fore-brain connected by stalkwith optic vesicle to), whoseanterior wall is partly invagi-nated: /. thickened and de-pressed lens-area. J<ii<iy0,{ Fig. 126.—Section through developingeye of eleven and a half day rabbit em-bryo (Piersol): B, fore-brain connectedwith optic vesicle (o), nearly effaced byapposition of invaginated anterior seg-ment (r) with posterior wall (p); /, lens-sac completely closed and separated fromectoderm ; I, tissue within secondary opticcup derived from surrounding mesoderm. firs


. An American text-book of obstetrics. For practitioners and students. o (Piersol): B,fore-brain connected by stalkwith optic vesicle to), whoseanterior wall is partly invagi-nated: /. thickened and de-pressed lens-area. J<ii<iy0,{ Fig. 126.—Section through developingeye of eleven and a half day rabbit em-bryo (Piersol): B, fore-brain connectedwith optic vesicle (o), nearly effaced byapposition of invaginated anterior seg-ment (r) with posterior wall (p); /, lens-sac completely closed and separated fromectoderm ; I, tissue within secondary opticcup derived from surrounding mesoderm. first trace of the visual organs appears very early—at the fifteenth day—as the conspicuous optic vesicles (Fig. 128),which are formed as lateral evagina-tions from the hinder part of the ante-rior primary brain-vesicle; later, whenthe optic vesicle opens into the cerebralcavity by means of the optic stalk, thelatter communicates with the inter-brain. The original optic vesicle soonexhibits indentation of its anterior wall(Fig. 125), the invagination progress- A B. Fig. 127.—Section through developing eye ofthirteen day rabbit embryo (Piersol): e, ectoderm ;/, lens, consisting of anterior nucleated divisionrepresenting thin front wall of lens-sac, and greatlythickened posterior division completely tilling cav-ity of sac by elongated fibres whose nuclei presentcrescentic zone (2); p, posterior pigmented layer :r, specialized anterior retinal layer: i, point wherelayers of optic vessels become continuous: n, ex-treme peripheral section of tissue of primitiveoptic nerve connected with vascular tunic (v) occu-pying posterior surface of lens: m, surroundingmesoderm, which (at 0 grows between lens andretina.


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Keywords: ., bookcentury1800, bookdecade1890, booksubjectobstetrics, bookyear1