Abstract:ObjectiveTo provide theoretical support for clinical sinus surgery by realizing the developmental rules and characteristics of the nasal structures, especially the basal lamellae and cells of ethmoidal bone, through the microanatomical observation of the fetal nasal structures of different gestational ages.MethodsNine (a total of 18 sides) fetal cadaveric head specimens of 24-38 weeks gestational age were obtained. The nasal mucosae were removed after median rupture, and the lamellar layers of the ethmoid as well as the bony or cartilaginous connections between the lamellae were observed.Results① From fetal weeks 24 to 38, uncinate process, middle turbinate, superior turbinate and supreme turbinate were presented in the ethmoid bone. The superior turbinate and ethmoid horizontal plate existed in the form of cartilage. The cephalic cartilagelike tissues of all lamellae were fused together with ethmoid horizontal plate to form skull base, and bony connections were found between adjacent lamellae on the lateral wall below the ethmoid bone. ② The cephalic end of uncinate process had an inverted Ushaped bone plate connection with the upper end of ethmoidal bulb, and the embryo frontal recess could be observed at early stage. ③The thickness of the lateral ethmoid wall was variable. Multiple bony ridges and depressions existing between adjacent lamellae got obvious with the gestational age. The depression formed by these bony ridges was early drainage pathway.ConclusionsMicroanatomical observations reconfirm the skeletal junction between the uncinate process and ethmoidal bulb as well as the level of the basal lamella in embryology. The bony bulges (also known as connecting plates) among adjacent lamellae on the lateral wall of the ethmoid divide interlamellar spaces into orderly drainage pathways, which establishes an anatomical basis for subsequent development of ethmoid sinus.