Embryology and secretory activity of labial salivary glands.

This study was carried out on the heads of 20 foetuses aged between 11 and 26 weeks. Four stages were distinguished in the development of labial salivary glands, each stage corresponding to gestational age. Stage I is characterized by a localized, rounded thickening of the stomodial epiblast into the mesenchyma of the mucosal side of the lower lip. This occurs at the 9th-10th week of gestation. Stage II is reached when the epiblastic thickening assumes the form of a single cord. It is oval when sectioned transversally and is the result of the proliferation of epiblastic cells into the underlying mesenchyma during the 11th-12th week. Stage III corresponds to a branching process which takes place at the 13th week. The single cord branches to form the future secretory lobes, which rapidly assume a grape-like appearance. The number of rudimentary glands increases during the first three stages of development, i.e. as long as the first formed glands have not developed ducts. Stage IV corresponds to the process of duct formation at the 18th week. Simultaneous differentiation of acinal and duct cells is observed and this procedes the onset of secretory activity.