The rudiment of the respiratory organs appears as a median longitudinal groove in the ventral wall of the pharynx.

The cephalic end opens into the pharynx through a slit-like aperture formed by the persistent anterior part of the groove.

Initially, the cephalic end is in open communication with the foregut, but eventually it becomes separated by the indentations of the mesoderm, the tracheoesophageal folds.

The right and left bronchial buds branch into main (primary), lobar (secondary), segmental (tertiary), and subsegmental bronchi and lead to the development of the lungs.

This article incorporates text in the public domain from page 1071 of the 20th edition of Gray's Anatomy (1918)