In the fourth week of development, the respiratory diverticulum,[1] starts to grow from the ventral (front) side of the foregut into the mesoderm that surrounds it, forming the lung bud.

[2] The epithelium of the larynx is of endodermal origin, but the laryngeal cartilages, unlike the rest of the respiratory bud connective tissue, come from the mesenchyme of the fourth and sixth pharyngeal arches.

The sixth pharyngeal arch, located around the laryngeal orifice, will become the thyroid, cricoid and arytenoid cartilages.

These structures are formed in a process in which the lining cells of the primitive larynx proliferate and occlude it.

During these stages, the terminal tubes narrow and give rise to small saccules, which become increasingly associated with capillaries as to make gas exchange possible.