A Reference handbook of the medical sciences embracing the entire range of scientific and practical medicine and allied science . f (Eimiithe, Phellan-drium, Sium, and others have more or less ileleteriousqualities. Henry U. Pushy. UMBILICAL CORD.—A knowledge of the develop-ment of the cord is prerequisite for understanding itsstructure at birth. Consequently its embryology will bedescribed first, then its general condition at term, andfinally the finer structureof its component parts. E-msryology.—In young human embryos the layer ofcells which later forins the skin does not encircle thebody.
A Reference handbook of the medical sciences embracing the entire range of scientific and practical medicine and allied science . f (Eimiithe, Phellan-drium, Sium, and others have more or less ileleteriousqualities. Henry U. Pushy. UMBILICAL CORD.—A knowledge of the develop-ment of the cord is prerequisite for understanding itsstructure at birth. Consequently its embryology will bedescribed first, then its general condition at term, andfinally the finer structureof its component parts. E-msryology.—In young human embryos the layer ofcells which later forins the skin does not encircle thebody. After covering the dorsal and lateral body wallsthislayer turns upoultself, and over the back of the em-bryo it meets and joins the corresponding layer from theopposite side, thus forming a closed transparent sac, the Uniblliral Cord. REFERENCE HANDBOOK OF THE MEDICAL SCIENCES. amniou (Fig. 4827, Am.). Since the body ?wall is thuslackini,^ on the ventral side, the intestinal tract is allowedto protrude. A great dilatation of the primitive intes-tine, the 3olk .sac, projects through this ventral opening. Am Fig. 4827.—Diagram of a Human Embryo S.!.! mm. Long. A part ofthe entoderma! tract is shown bv dotted lines. .4/«., Amnion;; body stalls: C/io., chorion; , yolk sac. (After W. His.) hounded b_y the line where the body wall is reflected toform the amnion. The yolk sac (Fig. 4827, ) is sur-rounded by an extension of the body cavity or ca? entire embryo, including the amnion, lies within ahollow sphere of tissue lined with mesoderm and coveredwith villous ectoderm. This is the chorion, a small frag-ment of which is drawn in Fig. 4827 (C/(0.). As madeknown by His, the human embr}0 is never free from thechorion, but is attached to it by a posterior continuationof the body, named the body stalk (Fig. 4827, ). If a cross section ofFig. 4827 weremade, passing be-tween the lettersC of C/io and Bof , the bodystalk would ap-pear as in Fi
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