The auditory system comprises the ears and their connections to and within the central nervous system. From the standpoint of physical layout, the auditory system may be divided into the outer, middle, and inner ears; the auditory nerve; and the central auditory pathways. The outer ear is made up of the pinna and ear canal. The eardrum separates the outer and middle ears, and is generally considered to be part of the latter. The middle ear also includes the tympanic cavity; the ossicular chain with its associated muscles, tendons, and ligaments; and the eustachian tube. The auditory nerve leaves the inner ear through the internal auditory canal, enters the brain at the angle of the pons and cerebellum, and terminates in the brainstem at the cochlear nuclei. The ear canal leads from the concha to the eardrum and varies in both size and shape.