. An American text-book of obstetrics. For practitioners and students. ks the estab-lishment of the segmentation which later is permanently effected by the devel-opment of the vertebrae and the associated parts of the trunk. The productionof the somites is so closely related to that of the mesoderm that the primaryarrangement of this important sheet must be recalled. After its origin fromthe double source of entoderm and ectoderm, the mesoderm rapidly expandslaterally, the growth being particularly active toward the caudal pole of theembryo, in consequence of which the layer becomes pyriform i
. An American text-book of obstetrics. For practitioners and students. ks the estab-lishment of the segmentation which later is permanently effected by the devel-opment of the vertebrae and the associated parts of the trunk. The productionof the somites is so closely related to that of the mesoderm that the primaryarrangement of this important sheet must be recalled. After its origin fromthe double source of entoderm and ectoderm, the mesoderm rapidly expandslaterally, the growth being particularly active toward the caudal pole of theembryo, in consequence of which the layer becomes pyriform in outline whenseen from its upper surface. At first a continuous sheet, the further develop-ment of the neural groove from above downward and of the notochord from 82 AMERICAN TEXT-BOOK OF OBSTETRICS. below upward soon divides the mesodermic tract along the embryonic axis intotwo great wings (Fig. 73). Each of these wings undergoes further differentiation into a paraxial bandnext the mid-line, and a lateral plate which blends away laterally into the Amnion. Mesoderm. Visceralmesoderm Pleuropericar-dial cavity. Pericardialplates. Extensionof celom. Fig. 73.—Transverse section of a sixteen and a half day sheep embryo (Bonnet). widely extending mesodermic area (Fig. 74). The lateral mesodermic plateundergoes cleavage into an upper and a lower lamina which respectivelyadhere to the ectoderm and the entoderm. The upper and outer of the result-ing two-layered lamellse constitutes the somatopleure; the under and inner one, Medullaryfurrow. Ectoderm. Uncleftmesoderm. Amnion.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectobstetrics, bookyear1
