Development of the human fetal lung in the pseudoglandular stage: scanning electron microscopic remarks.

The lung buds of 15 human fetuses from the 9th to the 14th week of i.u. life were examined by scanning electron microscopy (SEM). SEM allows to clearly evidentiate the branching pattern of the respiratory tree, the development of the vascular network, the differentiation of the layers in the bronchial wall and the maturation of the epithelium. Particularly, as concerns the epithelium, its pattern in the air conducting ways and in the respiratory zone appears to be different from the very start; the presence of vascular spaces and then of well-defined vessels can be already detected starting from the 9th week of development.