[Comparative studies of the endolymphatic sac and duct in embryonic skull (author's transl)]

The endolymphatic sac and duct were studied in 25 embryonic ears of humans between the 10th and 25th week of development. In the early stage the anlage develops as a protrusion medio-caudally from the utricle. During further development vacuoles appear within the connective tissue surrounding the duct and sac which eventually unite with the endolymphatic system enlarging the endolymphatic space as an answer of the connective tissue to the expansion and proliferation of the endothelium. In older specimens (fronto-occipital diameter: 40 mm) we find a tongue-like projection of the wall of the duct into the utricle known as the endolymphatic valve. This structure is covered with a thickened folded epithelium. It is stabilized by fibrous, cartilaginous, and bony tissue. Under normal conditions it therefore seems improbable that it can serve as a valve as supposed by other authors. The proliferation of endothelium and a concentration of blood vessels in this might indicate a higher metabolic activity with a biochemical filtering mechanism.