Normal development of the middle ear in the mouse: a light microscopic study of serial sections.

Development of the ear, especially the middle ear, was studied histologically in ddN and CF mice. Primordia of the 3 ossicles and the otic capsule appeared on day 12 of pregnancy. The stapedial primordium was observed as a mass of mesenchymal cells lateral to the primordium of the otic capsule, attaching to the medial part of the facial nerve. On day 13, the stapedial primordium continued to develop with the Reichert's cartilage. On day 14, the malleus and incus were differentiated. On day 15, the 3 ossicles were mostly completed in shape, and the stapedial footplate had a bilaminar structure at this stage. This structure appeared to correspond to the lamina stapedialis in the developing human stapes.