Archive image from page 459 of The development of the human. The development of the human body : a manual of human embryology . developmentofhum00mcmu Year: 1914 448 THE EYE of the optic bulb becomes pushed inward toward the inner wall, and this invagination continuing until the two walls come into contact, the bulb is transformed into a double-walled cup, the optic cup, in the mouth of which lies the lens (Fig. 268). The cup is not perfect, however, since the invagination affects not only the optic bulb, but also extends medially on the posterior surface of the stalk, forming upon this a lon
Archive image from page 459 of The development of the human. The development of the human body : a manual of human embryology . developmentofhum00mcmu Year: 1914 448 THE EYE of the optic bulb becomes pushed inward toward the inner wall, and this invagination continuing until the two walls come into contact, the bulb is transformed into a double-walled cup, the optic cup, in the mouth of which lies the lens (Fig. 268). The cup is not perfect, however, since the invagination affects not only the optic bulb, but also extends medially on the posterior surface of the stalk, forming upon this a longitudinal groove and producing a defect of the ventral wall of the cup, known as the chorioidal fissure (Fig. 267). The groove and fissure become occupied by mesodermal tissue, and in this, at about the fifth week, a blood-vessel develops which traverses Fig. 267.—Reconstruction of the Brain of an Embryo of Four Weeks, showing the Chorioid Fissure.—(His.) the cavity of the cup to reach the lens and is known as the arteria hyaloidea. In the meantime further changes have been taking place in the lens. The ectodermal depression which represents it gradually deepens to form a cup, the lips of which approximate and finally meet, so that the cup is converted into a vesicle which finally sepa- rates completely from the ectoderm (Fig. 268), much in the same way as the otocyst does. As the lens vesicle is constricted off, the surrounding mesodermal tissue grows in to form a layer between it and the overlying ectoderm, and a split appearing in the layer
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