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Stage 13 embryos have a greatest length of 3.9 to 6 mm and an estimated postfertilization age of 30 to 33 days. There are 30 or more pairs of somites or body segments along the body axis. The retinal part of the optic vesicle and the lens disc can be identified. The caudal neuropore is closed resulting in a completely closed neural tube. The lower limb bud has formed. The stomach and omphalomesenteric duct are present. The right and left lung buds form, which are the precursors of the primary bronchi.


New structures include C-2 spinal ganglion, endocardium, hepatocardiac vein, lamina terminalis, neural canal, root of trigeminal nerve (CN V).

Section 109

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Preparation for microscopic examination

Preparation for microscopic examination

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