Three-Week Embryo

#367, Slide 2 of 21

3 weeks

From The Biology of Prenatal Development.

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Note:

The first hint of central nervous system development (brain and spinal cord) occurs about 18 days after fertilization with the appearance of the neural folds.

Label Key:

1. midbrain

2. forebrain

3. hindbrain

4. somites

All ages referenced to fertilization, not last menstrual period.