. Cunningham's Text-book of anatomy. Anatomy. Trophoblast of _ chorion Mesoderm chorion Mesoderm of - amnion Ectoderm of- amnion Neural crest Roof-plate" Lateral wall of, neural groove Floor-plate'' Entoderm^' Mesoderm entoderm vesicle'" Cavity entoderm vesicle Fig. 36.—Transverse Section of a Zygote, showing early stage- of development of embryonic ccelom and differentiation of mesoderm. Noto- chord Neural crest Neural tube. Ectoderm of amnio] Mesoderm, of amnion Trophoblast of chorion Paraxial mesoderm j Intermediate cell tract Splanchnic and somatic layers of later
. Cunningham's Text-book of anatomy. Anatomy. Trophoblast of _ chorion Mesoderm chorion Mesoderm of - amnion Ectoderm of- amnion Neural crest Roof-plate" Lateral wall of, neural groove Floor-plate'' Entoderm^' Mesoderm entoderm vesicle'" Cavity entoderm vesicle Fig. 36.—Transverse Section of a Zygote, showing early stage- of development of embryonic ccelom and differentiation of mesoderm. Noto- chord Neural crest Neural tube. Ectoderm of amnio] Mesoderm, of amnion Trophoblast of chorion Paraxial mesoderm j Intermediate cell tract Splanchnic and somatic layers of lateral plate Notochord' Meso. of yolk-sac Entoderm of yolk-sac \ Extra-embryonic coilom Alimentary canal Yolk-sac Fig. 37.—Transverse Section of a Zygote, showing union of intra- and extra-embryonic parts of ccelom and separation of embryonic mesoderm into paraxial bars, intermediate tracts, and lateral plates, with separation of lateral plates into somatic and splanchnic layers by the intra-embryonic part of the ccelom. appears; this is the primitive streak(, 34). It is formed by the proliferation of the ecto- mesodermal cells of the wall of the larger inner vesicle. The deeper cells of the streak, which displace the primary mesoderm from the median plane, and thus come into contact with the entoderm, are the rudiments of the secondary or primitive streak mesoderm (Fig. 34). The superficial cells form part of the surface ectoderm of the embryo. At the anterior end of the primitive streak the mesoder- mal elements of the streak fuse with the subjacent entoderm and through the fused mass a perforation, the neurenteric canal (p. 23), is formed (Fig. 32). The canal itself soon dis- appears, but the cells of its walls form a nodal growing point, and by their proliferation the length and breadth of the embryonic area are increased. The mesoderm cells proliferated from the cephalic border of the nodal point are the rudiments of the notochord, which has already been cons
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1914
