Normal Development of the Middle and Inner Ear of the Mouse

The authors studied on the development of the ear, especially of the middle ear, in ddN and CF strain mice histologically.Materials included 54 normal mouse fetuses ranging from 7 to 18 of gestation. Their heads were serially sectioned and stained with hematoxyline and eosin.Results were as follows.The otic vesicle appeared on the day 9 of gestation and then the ear began to develop.Primordia of the 3 ossicles and the otic capsule appeared on the day 12. The facial nerve ran transversely close to the vestibular portion in the region of the otic capsule.Stapedial primordium was observed as a mass of mesenchymal cells laterally to the primordium of the otic capsule, attached to the medial part of the facial nerve.On the day 13, the stapedial primordium still continued to develop with Reichert's cartilage.On the day 14, the malleus and incur were not differentiated histologically.On the day 15, the 3 ossicles were mostly completed in shape and the stapedial footplate seemed to have a bilaminar structure at this stage.