. The elements of embryology . Embryology. VI.] THE EYE. 135. Diagrammatic Sections illustrating the Formation op THE Eye. (After Eemak.) In A, the tMn superficial epiblast A is seen to be thickened at x, in front of the optic vesicle, and involuted so as to form a pit 0, the mouth of which has already begun to close in. Owing to this involution, which forms the rudiment of the lens, the optic vesicle is doubled in, its front portion r being pushed against the back portion u, and the original cavity of the vesicle thus reduced in size. The stalk of the vesicle is shewn as stiU. broad. In 5, th
. The elements of embryology . Embryology. VI.] THE EYE. 135. Diagrammatic Sections illustrating the Formation op THE Eye. (After Eemak.) In A, the tMn superficial epiblast A is seen to be thickened at x, in front of the optic vesicle, and involuted so as to form a pit 0, the mouth of which has already begun to close in. Owing to this involution, which forms the rudiment of the lens, the optic vesicle is doubled in, its front portion r being pushed against the back portion u, and the original cavity of the vesicle thus reduced in size. The stalk of the vesicle is shewn as stiU. broad. In 5, the optic vesicle is still further doubled in so as to form a cup with a posterior wall u and an anterior wall r. In the hollow of this cup Hes the lens I, now completely detached from the superficial epiblast x. Its cavity is still shewn. The cavity of the stalk of the optic vesicle is already much narrowed. blast, which forms a continuous layer in front of it, all traces of the original opening being lost. There is thus left lying in the cup of the secondary optic vesicle, an isolated elliptical mass of epiblast. This is the rudiment of the lens. The small cavity within it speedily becomes still less by the thickening of the walls, especially of the hinder one. At its first appearance the lens is in immediate contact with the anterior wall of the secondary optic vesicle (Fig. 47 jB). In a short time, however, the lens. 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 Foster, M. (Michael), Sir, 1836-1907; Balfour, Francis M. (Francis Maitland), 1851-1882; Sedgwick, Adam, 1854-1913; Heape, Walter, 1855-1929. London ; New York : Macmillan
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Keywords: ., bookcentury1800, bookdecade1880, bookpubli, booksubjectembryology
