. The science and art of midwifery. ndred diameters), t w,*the dorsal plates have closed to form tubusmedullaris; the connection with the outer or cutaneous layer (c) is broken off; ; v, vertebral chords ; a p, the abdominal plates, have separated into an externaland internal stratum, united at m to form the mesenteric folds. The intermediate layer (mesoderm) now separates into an internaland external stratum, the existence of which, it has been noted, wasindicated at an earlier stage. These two strata remain united by theirinner borders, and form later at the point of union the mesen
. The science and art of midwifery. ndred diameters), t w,*the dorsal plates have closed to form tubusmedullaris; the connection with the outer or cutaneous layer (c) is broken off; ; v, vertebral chords ; a p, the abdominal plates, have separated into an externaland internal stratum, united at m to form the mesenteric folds. The intermediate layer (mesoderm) now separates into an internaland external stratum, the existence of which, it has been noted, wasindicated at an earlier stage. These two strata remain united by theirinner borders, and form later at the point of union the mesentericfolds. The outer extremities of the inner of these strata now curveinward, and finally unite together to form the intestine. They in-close at the same time the internal layer of the blastodermic mem-brane (entoderm). The closure, unlike that of the dorsal plates,takes place from front to rear, as wrell as from the two sides. The in-testinal tube is thus formed from the inner stratum of the mesoderm,4 50 PHYSIOLOGY OF THE which furnishes the fibro-muscular tissues, and from the internalblastodermic layer (entoderm), from which the glandular structuresare derived. A portion of the blastodermic vesicle is, however, notincluded in the intestinal tube, but hangs, during the early months ofgestation, from the body of the embryo, and is termed the umbilicalvesicle (u v). Finally the outer or cutaneous layer of the blastoder-mic membrane (ectoderm) and the outer stratum of the mesoderm(the fibro-muscular layer of the trunk) curve forward and inward so as to inclose a long cavity, theccelum, which surrounds the in-testine. This cavity in mam-mals subsequently becomes divid-ed by the diaphragm into thoraxand abdomen. The body of the embryo, seenin profile, at the time thesechanges are going on, possessesa thickened anterior, or cephalicportion, and a tapering posteriorextremity. It manifests at anearly period a tendency to elevateitself above the level of the areagerminativa.
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Keywords: ., bookcentury1800, bookdecade1890, bookidsci, booksubjectobstetrics
