The organization of the horizontal semicircular duct, ampulla and utricle in the rat and guinea pig.

Microdissections of the labyrinth of the guinea pig and rat were carried out with the labyrinth in place in the skull. This enabled photographs to be taken from a standardized identified orientation so as to show the relation of the horizontal semicircular duct and utricle to the planes of the head, and changes in the horizontal duct and utricle during development. It was also possible to show, for the first time, the relation of the horizontal duct and utricle to major brainstem structures. Photographic evidence is presented of the distribution of dark cells around the horizontal duct and ampulla in the guinea pig and of postnatal developmental changes in dark cells in the rat.