A Reference handbook of the medical sciences embracing the entire range of scientific and practical medicine and allied science . in most mam-mals, but not in the horse (Bonnet). In man, rarely thetwo veins remain apart. The umbilical arteries some-times fuse as reported by Hyrtl—a very uncommon oc-currence. The further development of the cord is chiefly a length-ening jirocess, due to the drawing away of the embryofrom the line of reflection of the body wall to form theamnion. The yolk stalk and are stretched outinto very slender tubes (Fig. 4831). The yolk sac remainsbetween the a
A Reference handbook of the medical sciences embracing the entire range of scientific and practical medicine and allied science . in most mam-mals, but not in the horse (Bonnet). In man, rarely thetwo veins remain apart. The umbilical arteries some-times fuse as reported by Hyrtl—a very uncommon oc-currence. The further development of the cord is chiefly a length-ening jirocess, due to the drawing away of the embryofrom the line of reflection of the body wall to form theamnion. The yolk stalk and are stretched outinto very slender tubes (Fig. 4831). The yolk sac remainsbetween the amnion and tlie chorion. A cross section of alater stage is found in Fig. 4830, B. The cadom has be-come quite small. It contains, at F, a mass of meso-derin, from which the entodermal yolk stalk, and theblood-vessels which accompanied it, have entirely disap-peared. Bridges of mesoderm form mesenterj-like struc-tures across the ccelom, and finally obliterate the cord then shows no trace of the yolk stalk. The CoitD at Birth.—At birth the cord is a smooth,glistening, white or pearly, apparently twisted rope of. Fig. 4S29.—Diagram of a Human Embryo, mm. Long. Letteringas in Fig. 4827. Iln part after W. His.) tissue extending from foetus to chorion. Its length isvariable, but is usualIj about cm.; the extremes aresaid to be 13 cm. and 1G7 cm., respectively. The hu-man cord is relatively much longer than that of other REFERENCE HANDBOOK OF THE MEDICAL SCIENCES. Vnibilical Cord. auimals. a ptculiarity correlated gratuitously ?with thegreat distention of the human amniotic cavit}. Its diam-eter, also viivial)le, averages 13 mm. The twistingof the cord, wliich begins in the second month, is gener-
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