The development of the human body; a manual of human embryology . stalk, at the ex-tremity of which is the yolk-vesicle. The further continu-ance of the folding in of theedges of the embryonic area Fig. 40.—Embryo mm. Long. , , . , am. Fragment of the torn am- leads to an almost complete nion; mg> medullary groove; closing in of the digestive J^ yolk-sac—(A lien Thomp- tract and reduces the opening through which the yolk-stalk and belly-stalk communicate with the embryonic tissues to a small area known as the umbilicus. An embryo which exhibits an early stage in the processof constricti
The development of the human body; a manual of human embryology . stalk, at the ex-tremity of which is the yolk-vesicle. The further continu-ance of the folding in of theedges of the embryonic area Fig. 40.—Embryo mm. Long. , , . , am. Fragment of the torn am- leads to an almost complete nion; mg> medullary groove; closing in of the digestive J^ yolk-sac—(A lien Thomp- tract and reduces the opening through which the yolk-stalk and belly-stalk communicate with the embryonic tissues to a small area known as the umbilicus. An embryo which exhibits an early stage in the processof constriction has been described by Allen Thompson andis represented in Fig. 40.* It measured about mm. inlength and had reached a stage in which the medullaryfolds had become very pronounced and their edges hadcome into contact at one portion, although the anteriorand posterior portions of the groove (mg) between them * It must be noted that in the figure neither the amnion (except for asmall fragment still persisting in front) nor the belly-stalk is 88 THE DEVELOPMENT OF THE HUMAN BODY. were still widely open. The embryo will be seen from thefigure to project somewhat both in front of and behind theyolk-sac, although the greater part of its ventral surface isstill formed by that structure. At the sides also it is wellseparated from the yolk-sac, and resting upon the sac infront is a swelling which represents the heart. In another embryo (Fig. 41), slightly smaller though
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
