Page 7 - SONO 260 THE FIRST TRIMESTER
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                                       ž By the end of week 4, the secondary yolk sac becomes wedged between these two membranes in an area called the chorionic cavity or extraembryonic coelom.
¡ The developing embryo is located between the yolk sac and amnion at 4 weeks.
ž At this time, the alimentary canal is formed. ¡ It will become the foregut, midgut, and hindgut.
ž The neural tube also begins to develop at this time. ¡ The neural tube will become the fetal head and spine.
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