The human ear consists of three regions called the outer ear, middle ear, and inner ear. The oval window, also known as the fenestra ovalis, is a connective tissue membrane located at the end of the middle ear and the beginning of the inner ear.
The fenestra ovalis connects the tiny bones of the middle ear to the scala vestibuli, which is the upper part of the cochlea. (The cochlea is the central organ of the inner ear.) The bone of the middle ear that actually connects to the fenestra ovalis is called the stirrup, or stapes.
The middle ear functions to transmit the motion of the eardrum (or tympanic membrane) to the inner ear. This increases the pressure on the connective tissue of the oval window. This pressure is ultimately transmitted through the stapes, which presses against the fenestra ovalis, to the cochlea. From there, it travels through the auditory nerve to the brain, which processes the sound.