8.4 The most important events in the third to eighth developmental weeks

• Introduction to the development processes during the third week (stages 6 to 7; ca. 17-19 days)
• Fourth week (stages 8 to 10; ca. 23-28 days)
  
• Fifth week (stages 11 to 14; ca. 29-33 days)
  
  • development of the pharyngeal arches
• Sixth week (stages 15 to 17; ca. 36-41 days)
  • development of the pharyngeal arches
• Fifth week (stages 11 to 14; ca. 29-33 days)
• Sixth week (stages 15 to 17; ca. 36-41 days)
• Seventh week (stages 18 to 20; ca. 44-49 days)
• Eighth week (stages 21 to 23; ca. 51-56 days)

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 18.

The heart musculature differentiates.

Hematopoiesis begins in the liver 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 19.