Cochlea to structures in the brainstem for further processing. The "stapes" (stirrup) ossicle bone of the middle ear transmits vibrations to the "fenestra ovalis" (oval window) on the outside of the cochlea, which vibrates the perilymph in the "vestibular duct" (upper chamber of the cochlea). The ossicles are essential for efficient coupling of sound waves into the cochlea, since the cochlea environment is a fluid–membrane system, and it takes more pressure to move sound through fluid–membrane waves than it does through air; a pressure increase is achieved by the area ratio of the tympanic membrane to the oval window, resulting in
Evolution of the cochlea apex of the cochlea faces more inferiorly in the hominins than the latter two groups. Finally, the cochlea of European middle Pleistocene hominins faces more inferiorly than Neanderthals, modern humans, and Homo erectus. Human beings, along with Apes, are the only mammals that do not have high frequency (>32 kHz) hearing. Humans have long cochleae, but the space devoted to each frequency range is quite large (2.5mm per octave), resulting in a comparatively reduced upper frequency limit. The human cochlea has approximately 2.5 turns around the modiolus (the axis). Humans, like many mammals and birds, are able to perceive auditory