Theearis theorganofhearing, and in mammalsbalance. In mammals, the ear is usually described as having three parts—theouter ear,middle earand theinner ear. Theouter ear consists of thepinnaand theear canal, and as the outer ear is the only visible portion of the ear in most animals, the word "ear" often refers to the external part alone.The middle ear includes thetympanic cavityand the threeossicles. Theinner ear sits in thebony labyrinth, and contains the semicircular canals, the utricle and saccule, and the cochlea. These facilitate a sense of balance and allow eye tracking when moving, allow a fixed sense of balance, and allow hearing, respectively. The ears ofvertebratesare placed somewhat symmetrically on either side of the head, an arrangement that aidssound localization.The ear develops from the firstpharyngeal pouchand six small swellings that develop in the earlyembryocalledotic placodes, which are derived fromectoderm.The ear may be affected by disease, including infection and traumatic damage. Diseases of the ear may lead tohearing loss,tinnitusandbalance disorderssuch asvertigo, although many of these conditions may also be affected by damage to the brain or neural pathways leading from the ear.