Seventh week (stages 18 to 20; ca. 44-49 days)
Numerous changes to the embryo's limbs happen in this week. The places where finger and toes arise become visible.
The interdigital necrosis zones (INZ) are also now clearly recognizable in the lower extremities (stage 18).
The heart musculature differentiates.
Hematopoiesis begins in the liver (stage 18).
The physiologic umbilical hernia is still present.
The ossification of the upper extremities has already begun. The head becomes rounded, raises and looks more and more human.
The cloacal membrane tears (stage 19).