Morphology of the seagull's inner ear.

The morphology of the seagull ear was investigated and found to be generally similar to that of other Aves. Several specific outer middle and inner ear features were found to be sufficiently different as to be remarkable. Most notably, the dual membranes of the external auditory meatus: one, a collecting (and possibly amplifying and reflecting) parabolic membrane chamber situated immediately anterior to the slightly deeper tympanic membrane. The convex tympanic membrane attaches a cartilagenous extracolumella and a thick osseous columella, which is less thin and fragile than that observed in domestic fowl of comparable body size. The columella footplate and round window are completely covered with a second middle ear membrane which apparently serves as an H2O seal and hydrostatic pressure matcher. The short, hard seagull cochlea houses an elaborate basilar papilla which contains thousands of short and tall hair cells, each with a systematic arrangement of stereocilia bundles. In the seagull, the length of the basilar papilla and the length, width, and number of stereocilia, features which affect the transduction process and frequency resolution, are different from those reported for certain other Aves.