Normal fetal weight: 1300 gm
Moore KL, Persaud TVN. 1998. The Developing Human: Clinically Oriented Embryology. 6th ed. Philadelphia: WB Saunders Co.
Respiratory bronchioles subdivide to produce terminal sacs (primitive alveoli) numbering between 20 and 70 million before birth.
Duration: 8 weeks
Larsen WJ. 1997. Human Embryology. New York: Churchill Livingstone Inc.