On the Structure of the Avian Maculae

The maculae of the labyrinths of several avian species were examined. The striola of the macula utriculi and lagenae is tri‐zonal, consisting of two zones of hair cells type I (HC I) located on each side of a middle zone of hair cells type II (HC II). An exception is the mute swan, in which the macula utriculi has a striola consisting of one broad zone of HC I. The macula sacculi is, in its central part, mainly consisting of HC I, and the striola does not have a tri‐zonal structure. The hair cells in the macula utriculi are polarized with their kinociliar end oriented towards the striola, while in the macula sacculi and lagenae they are oriented away from this dividing line. A varying number, from 1 to 12, of HC I are enclosed within the same nerve chalice. The macula sacculi seems to contain chalices with slightly more HC I than the two other maculae do.