The early development of the larynx in staged human embryos. I. Embryos of the first five weeks (to stage 15).

Abstract

More than 15 serially sectioned human embryos from stage 8 to stage 15 were examined, together with relevant reconstructions and photographs. Their lengths ranged from 1 to 7 mm, and their ages from 18 to 33 postovulatory days. The necessity of employing a recognized staging system is stressed. The foregut appears either late in stage 8 or during stage 9. The median pharyngeal groove that appears during stage 9 presages the first indication of the respiratory system and includes the future larynx. The laryngotracheal sulcus begins to be circumscribed at stage 10 and a caudal expansion represents the pulmonary primordium. The tracheoesophageal septum appears at stage 12. The right and left lung buds become definite by stage 13. The hypopharyngeal eminence, arytenoid swellings, and epithelial lamina of the larynx are detectable at stage 14. Vestibulotracheal and pharyngotracheal canals are distinguishable at stage 15. Hence, from the first appearance of the foregut at about 19 days, the larynx has developed into a recognizable organ two weeks later, namely, by 33 days.