A system of obstetrics . , BOOn becomes indistinct ; tracesOf it may, however, be found later in the mesoblastic BOmib - These new foldings, known as the side-folds or lateral folds, serve,with the head- and tail-folds, to separate off a -mailer upper cavity ofthe blastoderm from a much larger lower part (non-embryonic part)which spreads over the food-yelk. There is, however, at this stage afree communication between the two cavities, and the smaller or embry-onic one contains food-yelk as well as the larger. If, now, the under side (Fig. 35) of the head-fold were to grow backward, and the und
A system of obstetrics . , BOOn becomes indistinct ; tracesOf it may, however, be found later in the mesoblastic BOmib - These new foldings, known as the side-folds or lateral folds, serve,with the head- and tail-folds, to separate off a -mailer upper cavity ofthe blastoderm from a much larger lower part (non-embryonic part)which spreads over the food-yelk. There is, however, at this stage afree communication between the two cavities, and the smaller or embry-onic one contains food-yelk as well as the larger. If, now, the under side (Fig. 35) of the head-fold were to grow backward, and the under side of the tail-fold forward, and the1 con-verging parts (Fig. 36) of the Bide-folds inward, there would be shutoil* more and more an upper smaller cavity from a lower and much THE EARLY STAGES OF DEVELOPMENT. 115 larger. Ultimately, the folds would all meet at one point, and if theycoalesced there would completely shut off the upper cavity. The dia-grams below will illustrate this condition (Figs. 37 and 38). Fig. 3. Diagram illustrating the Meeting of the Head- and Tail-folds at the Navel to close off the embryofrom the yelk-sac cavity. No attempt has been made to indicate the various layers of theblastoderm. Em, embryonic tube; Ys, part of yelk-sac; Yk, food-yelk; Al, alimentary canal,nearly closed; ph, embryonic pharynx; re. embryonic rectum; the buccal and anal open-ings are pitted in from the exterior at a much later stage of development; H, head-fold ; T,tail-fold; Ne, neural canal. Fig. 38.
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectobstetrics, bookyear1
