Z8600021 at 22:52, 18 August 2012

2012-08-18T22:52:36Z

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	Optic cup and choroidal fissure seen from below, from a human embryo of about four weeks. (Kollmann.)		Optic cup and choroidal fissure seen from below, from a human embryo of about four weeks. (Kollmann.)

			===Development===

			The eyes begin to develop as a pair of diverticula from the lateral aspects of the forebrain. These diverticula make their appearance before the closure of the anterior end of the neural tube; after the closure of the tube they are known as the optic vesicles. They project toward the sides of the head, and the peripheral part of each expands to form a hollow bulb, while the proximal part remains narrow and constitutes the optic stalk (Figs. 863, 864). The ectoderm overlying the bulb becomes thickened, invaginated, and finally severed from the ectodermal covering of the head as a vesicle of cells, the lens vesicle, which constitutes the rudiment of the crystalline lens. The outer wall of the bulb becomes thickened and invaginated, and the bulb is thus converted into a cup, the optic cup, consisting of two strata of cells (Fig. 864). These two strata are continuous with each other at the cup margin, which ultimately overlaps the front of the lens and reaches as far forward as the future aperture of the pupil. The invagination is not limited to the outer wall of the bulb, but involves also its postero-inferior surface and extends in the form of a groove for some distance along the optic stalk, so that, for a time, a gap or fissure, the choroidal fissure, exists in the lower part of the cup (Fig. 865). Through the groove and fissure the mesoderm extends into the optic stalk and cup, and in this mesoderm a bloodvessel is developed; during the seventh week the groove and fissure are closed and the vessel forms the central artery of the retina. Sometimes the choroidal fissure persists, and when this occurs the choroid and iris in the region of the fissure remain undeveloped, giving rise to the condition known as coloboma of the choroid or iris.

	(Text modified from Gray's 1918 Anatomy)		(Text modified from Gray's 1918 Anatomy)

Z8600021: ==Human Optic Cup and Choroidal Fissure== Optic cup and choroidal fissure seen from below, from a human embryo of about four weeks. (Kollmann.) (Text modified from Gray's 1918 Anatomy) {{Gray Anatomy}} Category:Cartoon Category:Senses [[Categ

2012-08-18T22:51:49Z

==Human Optic Cup and Choroidal Fissure== Optic cup and choroidal fissure seen from below, from a human embryo of about four weeks. (Kollmann.) (Text modified from Gray's 1918 Anatomy) {{Gray Anatomy}} Category:Cartoon Category:Senses [[Categ

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==Human Optic Cup and Choroidal Fissure==

Optic cup and choroidal fissure seen from below, from a human embryo of about four weeks. (Kollmann.)

(Text modified from Gray's 1918 Anatomy)

{{Gray Anatomy}}

[[Category:Cartoon]]
[[Category:Senses]] [[Category:Vision]] [[Category:Human]] [[Category:Week 4]]

File:Gray0865.jpg - Revision history

Z8600021 at 22:52, 18 August 2012

Z8600021: ==Human Optic Cup and Choroidal Fissure== Optic cup and choroidal fissure seen from below, from a human embryo of about four weeks. (Kollmann.) (Text modified from Gray's 1918 Anatomy) {{Gray Anatomy}} Category:Cartoon Category:Senses [[Categ