Description: This stock medical illustration features a side cut view through the uterus, chorionic villi, chorionic sac, chorionic cavity and amniotic sac containing a human embryo in the fourth week of development (first month of pregnancy). At this stage the embryo has a C-shaped curve. The caudal neuropore is closed. The upper limb buds are like flippers and the lower limb buds have begun to form. Four pairs of branchial or pharyngeal arches are visible and the lens placodes (primitive eyes) are distinct. Otic pits are also present (primitive ears). The curled tail with its somites (primitive vertebrae) is a characteristic feature of this stage. The heart prominence is also easily recognized.
Last Updated: Jul 14th, 2020
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