The lung primordia

An endodermal diverticulum arises at the medial and ventral aspects of the foregut. It bulges outwards as the laryngotracheal ridge. At S10, from inside it appears as the laryngotracheal groove (sulcus laryngotrachealis). The cranial part of this diverticulum develops into the larynx, while the caudal part becomes the lung anlage or lung bud. The larynx remains connected with the foregut caudal to the hypopharyngeal eminence via the aditus of the larynx. The lung anlage grows caudally to form a stalk, the future trachea, before dividing into the left and right lung buds. The mesenchyme between the lung anlage and the foregut is called the tracheo-oesophageal septum. In relation to the vertebral column, the position of the aditus of the larynx remains constant while the division point of the trachea into the two lungs (bifurcation of trachea) descends.