[A brief history of hearing research. III. Microscopic anatomy]

The present review provides merely a glimpse of the vast field of modern anatomy of the ear, which began with the introduction of the light microscope and histological techniques. Owing to the poor accessibility and small size of the inner ear, the investigation of its structure was highly dependent on the development of modern histological techniques, i.e. fixation, embedding, sectioning and staining of tissue, which took place in the 19th century. In 1824 Huschke discovered the papilla spiralis acoustica and in 1851 Corti described the structure of the sensory epithelium of the inner ear, and also detected the outer hair cells. A little later Deiters also found the inner hair cells, while Leydig discovered the stereocilia on the hair cells. In 1863 Hensen showed that the hair cells were provided with nerve endings, but it was Retzius who proved that the nerve fibres terminate at the basal end of the hair cells. He concluded from his studies that the hair cells are the actual receptors of the organ of hearing. Hensen, Retzius and Held provided morphometric data of the cochlea which are still largely valid today. In 1926 Held managed to isolate single hair cells. He also described two different types of nerve fibre in the cochlea. In 1926, Kolmer was the first to propose that apart from afferent nerve fibres there might also be an efferent innervation of the cochlea. In 1942 this was confirmed by Rasmussen. In animal experiments, he and others demonstrated the efferent nature of the olivo-cochlear bundle by dividing the nerve, which subsequently showed secondary descending degeneration.(ABSTRACT TRUNCATED AT 250 WORDS)