Week 7 of development

◦CONNECTION BETWEEN THE GUT AND YOLK SAC consists of only the small yolk stalk

◦THE LIMBS change markedly during this week

Week 8 of development

This is the final week of the embryonic period

◦THE FINGERS are noticeably webbed and short

◦NOTCHES now are seen between the toe rays, and the tail bud is still visible

◦THE LIMB REGIONS are clear, fingers lengthen, toes are distinct, and the tail bud disappears by the end of this week

◦THE EMBRYO has human characteristics, but the head is distinctly large (about one-half of embryo)

◦THE EYES usually open, but near the end of week 8 the eyelids begin to meet and fuse

◦THE EXTERNAL EARS (AURICLES) assume their final shape but are still low set

◦THE EXTERNAL GENITALIA are not distinct enough for accurate sexual identification

External Embryo Appearance

◦BY THE END OF WEEK 4 the embryo has about 28 somites, the ventral body wall has closed, and the major external features are somites and pharyngeal arches. The age of the embryo now is often expressed in somites or as the crown-rump (CR) length (sitting height) in millimetres. The standing height or crown-heel (CH) length is sometimes used for 8-week and older specimens, but these are hard to make accurately

◦THE EXTERNAL APPEARANCE during month 2 changes due to the great size of the head and formation of the limbs, ears, nose, and eyes. By the beginning of week 5, the fore- and hind-limbs appear as paddle-shaped buds

◦AGE ESTIMATION usually relies on 2 commonly used references, namely, the onset of the last menstrual period (LMP) and the time of fertilization

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