Pressure equilibration in the penguin middle ear.

CONCLUSIONS: King penguins have a venous structure in the form of a corpus cavernosum (CC) in their middle ear (ME) submucosa. The CC may be viewed as a special organelle that can change ME volume for pressure equilibration during deep-sea diving it is a pressure regulating organelle (PRO). A similar CC and muscles also surround the external ear (EE) and may constrict it, isolating the tympanic membrane from the outside. A CC was previously found also in the ME of marine diving mammals and can be expected to exist in other deep diving animals, such as marine turtles.
OBJECTIVES: Marine animals require equalization of middle ear (ME) pressure when diving hundreds or thousands of meters to catch prey. We investigated what mechanism enables king penguins to protect their ME when they dive to great depths.
MATERIALS AND METHODS: Biopsies and serial sections of the ME and the EE of the deep diving king penguin (Aptenodytes patagonicus) were examined microscopically.
RESULTS: It was demonstrated that the penguin ME has an extensive network of small and large submucosal venous sinuses. This venous formation, a corpus cavernosum, can expand and potentially 'flood' the ME almost completely on diving, thus elevating ME pressure and reducing the ME space. The EE has a similar protective mechanism.