Editing Inner ear (section)

==Other animals==
Birds have an auditory system similar to that of mammals, including a cochlea. Reptiles, amphibians, and fish do not have cochleas but hear with simpler auditory organs or vestibular organs, which generally detect lower-frequency sounds than the cochlea.  The cochlea of birds is also similar to that of crocodiles, consisting of a short, slightly curved bony tube within which lies the basilar membrane with its sensory structures.<ref>{{Cite web|url=https://www.britannica.com/science/sound-reception/Hearing-in-birds|title=Bird cochlea}}</ref>

===Cochlear system===
{{See also|Evolution of the cochlea}}
In [[reptile]]s, sound is transmitted to the inner ear by the [[stapes]] (stirrup) bone of the middle ear. This is pressed against the [[oval window]], a membrane-covered opening on the surface of the vestibule. From here, sound waves are conducted through a short '''perilymphatic duct''' to a second opening, the [[round window]], which equalizes pressure, allowing the incompressible fluid to move freely. Running parallel with the perilymphatic duct is a separate blind-ending duct, the '''lagena''', filled with [[endolymph]]. The lagena is separated from the perilymphatic duct by a [[basilar membrane]], and contains the sensory hair cells that finally translate the vibrations in the fluid into nerve signals. It is attached at one end to the saccule.<ref name=VB>{{cite book |author=Romer, Alfred Sherwood|author2=Parsons, Thomas S.|year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders International |location= Philadelphia, PA|pages= 476–489|isbn= 003910284X}}</ref>

In most reptiles the perilymphatic duct and lagena are relatively short, and the sensory cells are confined to a small '''basilar papilla''' lying between them. However, in [[mammal]]s, [[bird]]s, and [[crocodilian]]s, these structures become much larger and somewhat more complicated. In birds, crocodilians, and [[monotreme]]s, the ducts are simply extended, together forming an elongated, more or less straight, tube. The endolymphatic duct is wrapped in a simple loop around the lagena, with the basilar membrane lying along one side. The first half of the duct is now referred to as the [[scala vestibuli]], while the second half, which includes the basilar membrane, is called the [[scala tympani]]. As a result of this increase in length, the basilar membrane and papilla are both extended, with the latter developing into the [[organ of Corti]], while the lagena is now called the [[cochlear duct]]. All of these structures together constitute the cochlea.<ref name=VB/>

In [[theria]]n mammals, the lagena is extended still further, becoming a coiled structure (cochlea) in order to accommodate its length within the head. The organ of Corti also has a more complex structure in mammals than it does in other [[amniote]]s.<ref name=VB/>

The arrangement of the inner ear in living [[amphibian]]s is, in most respects, similar to that of reptiles. However, they often lack a basilar papilla, having instead an entirely separate set of sensory cells at the upper edge of the saccule, referred to as the '''papilla amphibiorum''', which appear to have the same function.<ref name=VB/>

Although many fish are capable of hearing, the lagena is, at best, a short diverticulum of the saccule, and appears to have no role in sensation of sound. Various clusters of hair cells within the inner ear may instead be responsible; for example, [[Osteichthyes|bony fish]] contain a sensory cluster called the '''macula neglecta''' in the utricle that may have this function. Although fish have neither an outer nor a middle ear, sound may still be transmitted to the inner ear through the bones of the skull, or by the [[swim bladder]], parts of which often lie close by in the body.<ref name=VB/>

===Vestibular system===
By comparison with the [[cochlea]]r system, the [[vestibular system]] varies relatively little between the various groups of [[gnathostome|jawed vertebrates]]. The central part of the system consists of two chambers, the saccule and utricle, each of which includes one or two small clusters of sensory hair cells. All jawed vertebrates also possess three semicircular canals arising from the utricle, each with an [[osseous ampullae|ampulla]] containing sensory cells at one end.<ref name=VB/>

An [[endolymphatic duct]] runs from the saccule up through the head and ending close to the brain. In [[cartilaginous fish]], this duct actually opens onto the top of the head, and in some [[teleost]]s, it is simply blind-ending. In all other species, however, it ends in an [[endolymphatic sac]]. In many reptiles, fish, and amphibians this sac may reach considerable size. In amphibians the sacs from either side may fuse into a single structure, which often extends down the length of the body, parallel with the [[spinal canal]].<ref name=VB/>

The primitive [[lamprey]]s and [[hagfish]], however, have a simpler system. The inner ear in these species consists of a single vestibular chamber, although in lampreys, this is associated with a series of sacs lined by [[cilia]]. Lampreys have only two semicircular canals, with the horizontal canal being absent, while hagfish have only a single, vertical, canal.<ref name=VB/>

===Equilibrium===
The inner ear is primarily responsible for balance, equilibrium and orientation in three-dimensional space. The inner ear can detect both static and dynamic equilibrium. Three [[semicircular ducts]] and two chambers, which contain the [[saccule]] and [[utricle (ear)|utricle]], enable the body to detect any deviation from equilibrium. The macula sacculi detects vertical acceleration while the [[macula utriculi]] is responsible for horizontal acceleration. These microscopic structures possess stereocilia and one kinocilium which are located within the gelatinous otolithic membrane. The membrane is further weighted with otoliths. Movement of the stereocilia and kinocilium enable the hair cells of the saccula and utricle to detect motion. The semicircular ducts are responsible for detecting rotational movement.<ref>Anatomy & Physiology The Unity of Form and Function. N.p.: McGraw-Hill College, 2011. Print.</ref>