Histogenetic Study on Human Fetal Lungs

Using 27 externally normal human fetuses ranging from the four to the tenth lunar months gestation (M) (7.3 to 36.0cm in crown-rump length), the histogenesis of the lung was examined by the conventional methods. A part of the middle lobe of the lung was sectioned and stained with hematoxylin and eosin, respectively.
The epithelia of the terminal buds were the columnar or the low columnar at the fourth M, the low columnar to the cuboidal at the fifth M and the cuboidal to the flattened at the sixth M. The difference of the nuclei's stainability between the tubuli appeared at the end of the fourth M, and became evident at the fifth M, and was clear at the sixth M. The proliferation of the capillaries appeared in the mesenchyme near the epithelium between the end of the fourth M and the beginning of the fifth M. Thereafter, the capillaries began to invade at the proximal part of the terminal buds and were exposed directly to the air spaces at the seventh M. The mesenchymal condensation and irregularity of arrangement of the epithelium appeared at the proximal part of the terminal buds.