Development of the utricular macula in the mouse.

There have been many studies reporting on the development of the utricular macula using transmission electron microscopy. This study demonstrates the morphological development of the utricular macula in the mouse using scanning electron microscopy. Utricular maculae from CBA/CBA mice were studied from the 11.5th gestational day to 2 weeks after birth. Between the 11.5th and 12.5th gestational day there are numerous microvilli and a primary cilium on the surface of the otocyst. Sensory hairs appear on the 13.5th gestational day. The kinocilium and stereocilia are short and the latter of almost equal in length. The polarity of the kinocilium is first noticed after the 16.5th gestational day. The formation of otoconia starts on the 14.5th gestational day. They are shaped like a dumb-bell and are oval and columnar. Otoconia with a hexagonal form are recognized after the 16.5th gestational day.