The mammalian ear has three major components: the outer, middle, and inner ears (Fig. 20.1). The outer ear consists of a cartilaginous flange, the pinna , incorporating a resonant cavity that connects to the ear canal Ear canal and finally to the tympanic membrane Tympanic membrane. It performs an initial filtering of the sound waves, increasing the sound pressure gain at the tympanic membrane in the 2- to 7-kHz region. It also aids sound localization. Bats, for example, have highly developed pinnae, with a high degree of directional selectivity. Although less efficient in humans, the outer ear accounts for our ability to distinguish whether sounds come from above or below, in front or behind.