A manual of practical obstetrics . tive tract, and the genito-urinary organs. 4. The Entoderm forms the epithelial lining and glands of 4 74 FECUNDATION AND NUTRITION OF OVUM. the intestinal tube. The vitelline membrane still surroundsand encloses all of these. In now studying the development of the ovum, it must firstbe understood that all the changes to be related take placeinside the vitelline membrane, which, though extremely thiu,delicate, and soft, really plays the part of a sort of eggshell,inasmuch as it contains all the other structures of the embryowith which we have to deal. Moreove
A manual of practical obstetrics . tive tract, and the genito-urinary organs. 4. The Entoderm forms the epithelial lining and glands of 4 74 FECUNDATION AND NUTRITION OF OVUM. the intestinal tube. The vitelline membrane still surroundsand encloses all of these. In now studying the development of the ovum, it must firstbe understood that all the changes to be related take placeinside the vitelline membrane, which, though extremely thiu,delicate, and soft, really plays the part of a sort of eggshell,inasmuch as it contains all the other structures of the embryowith which we have to deal. Moreover, the vitelline mem-brane does not break until the end of pregnancy, though, aswe shall see, it becomes lost by extreme attenuation, and byamalgamation with other membranes lining its inner surface. If, now, at a very early stage of development, we supposethe vitelline membrane to be cut open and removed artificially,it would bring into view the outer surface of the externalblastodermic membrane (the epiblast, ectoderm, or serous.
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