The vibrations from the eardrum set the ossicles into motion. The ossicles are three tiny bones, and in fact are the smallest in the human body. They’re named the malleus (hammer), incus (anvil), and stapes (stirrup), which all work to further amplify the sound.
The stapes attaches to the oval window that connects the middle ear to the inner ear. The eustachian tube, which opens into the middle ear, is responsible for equalizing the pressure between the air outside the ear to that within the middle ear.