Human Anatomy & Physiology (9th Edition)

Published by Pearson
ISBN 10: 0321743261
ISBN 13: 978-0-32174-326-8

Chapter 28 - Pregnancy and Human Development - Review Questions - Page 1093: 5

Answer

A

Work Step by Step

The allantois is a sac-like structure which after 3 to 5 weeks starts forming blood, and that leads to that blood formation becoming the arteries and veins of the embryo.
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