Prenatal development of the human trachea

The tracheas of 46 human foetuses were examined: 26 male, 20 female with C-R length of 99-255 mm. The analysis of the total length of the trachea was carried out and its transverse dimension was presented on three levels: on the first tracheal cartilage, in the mid-length of the trachea, and at the bifurcation into the main bronchi; also the proportions between these dimensions and the C-R length were analysed. The length of the trachea was measured in a straight line--from the end of larynx to the bifurcation of the trachea. Comparing tracheas to a tunnel with two openings, it was observed that the transverse dimension, the "laryngeal", is greater than the "bronchial"--in the case of smaller foetuses by 2 mm, but in foetuses with C-R length of over 250 mm by 1 mm. Moreover, no significant differences between male and female sex were noticed. All the measurements were taken with the use of a slide caliper. The results should be useful in the detection of abnormalities in the structure of the trachea, in problems with respiratory physiology and in endotracheal intubation, endoscopy or tracheostomy.