. The elements of Embryology,. 126 THE THIRD DAY. [chap. FiGf. Section through the Dorsal Region of an Embrto at the commencement OF the Third Dat. M. C. medullary canal. Ch. notochord. p. v. protovertebra composed of an investment of columnar cells enclosing a central nucleus of rounded cells. w. d. Wolffian duct, which has commenced to travel doWn from the dorsal surface of the mesoblast. A. o. dorsal aorta of right side. g. e. germinal epithelium; an epitlieliimi of columnar cells lining the upper end of thepleuro- peritoneal cavity, and which is related to the formation of MuUer's duc
. The elements of Embryology,. 126 THE THIRD DAY. [chap. FiGf. Section through the Dorsal Region of an Embrto at the commencement OF the Third Dat. M. C. medullary canal. Ch. notochord. p. v. protovertebra composed of an investment of columnar cells enclosing a central nucleus of rounded cells. w. d. Wolffian duct, which has commenced to travel doWn from the dorsal surface of the mesoblast. A. o. dorsal aorta of right side. g. e. germinal epithelium; an epitlieliimi of columnar cells lining the upper end of thepleuro- peritoneal cavity, and which is related to the formation of MuUer's duct and of the ovary. S. o. somatopleure. s. p. splanchnopleure. The splanchnopleure is very little folded in, the embryonic sac being in this middle region widely open to the yolk below. The somatopleure is much more folded in. At a little distance outside the protovertebra is a ridge with thickened mesoblast, the Wolffian ridge, marking the line along which the limbs will be developed. Beyond this ridge the somatopleure suddenly descends to form the bodj'-wall (of the abdomen); it then ascends, and after a fold, probably due to the action of the chromic acid, forms an angular projection at about the level of the protovertebra. This projection is the lateral fold of the amnion, the section having been taken just at that point between the head and tail where the amnion is, on the third day, least developed. Beyond the amniotic fold the somatopleure and splanchnopleure come into apposition, and still farther out completely coalesce. It will be observed that the pleuroperitoneal space already reaches laterally far beyond the limits of the embryo itself. In the splanchnopleure is seen at F a section of a large branch of the omphalo-mesaraic trunk. The shading of the general mesoblast is diagrammatic. The width of the cavity of the neiu-al tube is unusually Please note that these images are extracted from scanned page images that may have been digitally enhanced for readabili
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Keywords: ., bookcentury1800, bookdecade1870, bookpublisherlondo, bookyear1874
