Form and function of the mammalian inner ear

Abstract

The inner ear of mammals consists of the cochlea, which is involved with the sense of hearing, and the vestibule and three semicircular canals, which are involved with the sense of balance. Although different regions of the inner ear contribute to different functions, the bony chambers and membranous ducts are morphologically continuous. The gross anatomy of the cochlea that has been related to auditory physiologies includes overall size of the structure, including volume and total spiral length, development of internal cochlear structures, including the primary and secondary bony laminae, morphology of the spiral nerve ganglion, and the nature of cochlear coiling, including total number of turns completed by the cochlear canal and the relative diameters of the basal and apical turns. The overall sizes, shapes, and orientations of the semicircular canals are related to sensitivity to head rotations and possibly locomotor behaviors. Intraspecific variation, primarily in the shape and orientation of the semicircular canals, may provide additional clues to help us better understand form and function of the inner ear.

Exceptional Skull of Huayqueriana (Mammalia, Litopterna, Macraucheniidae) From the Late Miocene of Argentina: Anatomy, Systematics, and Paleobiological Implications

“…The secondary crus commune is also absent in Macrauchenia and Diadiaphorus, and the notoungulates Notostylops, Altitypotherium, Pachyrukhos, and Cochilius, but it is present in Early Eocene litopterns (Macrini et al, 2010(Macrini et al, , 2013Billet et al, 2015). The secondary crus commune is a plesiomorphic trait for mammals (e.g., Meng and Fox, 1995;Ekdale, 2016), evidently retained in basal litopterns but subsequently lost in later members of the group (Billet et al, 2015).…”

“…The vestibule contains the membranous utricule and saccule (Meng and Fox, 1995;Macrini et al, 2010;Ekdale, 2016). In IANIGLA-PV 29 the vestibule is rostrocaudally elongated, parallel to the main axis of the LSC.…”

“…As in all mammals, the labyrinth consists of a series of interconnected spaces within the petrosal, including the cochlea, vestibule, and the three semicircular canals (e.g., MacIntyre, 1972;Ekdale, 2013Ekdale, , 2016. The cochlear canal NO.…”

Digital reconstruction of the inner ear of Leptictidium auderiense (Leptictida, Mammalia) and North American leptictids reveals new insight into leptictidan locomotor agility

“…Based on the study by Ekdale and Rowe (2011) and further recent works Luo et al 2012;Ekdale 2013Ekdale , 2015, we propose that thin and distinctly arcuate semicircular canals and the presence of a secondary crus commune, as present in all of our Leptictida, are plesiomorphic features of the leptictidan groundplan (in the sense of Hennig 1950). Mesozoic (Meng and Fox 1995;Ekdale and Rowe 2011;Ekdale 2015). The precise pattern in Leptictis remains ambiguous, because our observation of 2.25 cochlear turns in Leptictis sp.…”

“…Thus, we propose that the secondary bony lamina is a plesiomorphic character of Leptictida and Theria as well. The secondary bony lamina is reduced several times independently in modern mammals (Fleischer 1973;Ekdale 2015). Leptictidium auderiense also shows a derived pattern concerning the absence of the secondary bony lamina.…”