The middle ear was the portion of the ear internal to the eardrum. It consisted of the malleus, incus, and stapes bones.
The microscope laser was a specialized medical instrument designed for middle ear healing. (TAS: "The Terratin Incident")
In 2371, while Kes was studying medical texts to become a nurse, The Doctor tested her on the bones of the middle ear, all of which she correctly quoted. (VOY: "Eye of the Needle")