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Hair Cell Morphology And Innervation In The Basilar Papilla Of
The Emu
(Dromaius Novaehollandiae)
FP Fischer
Institut fur
Zoologie
Technische
Universit at Munchen
Garching, Germany
24 1998 Jul
The emu, being a member of the rather primitive
bird group of the palaeognathid Ratitae, may reveal primitives features of
the avian basilar papilla. There are, however, no qualitative differences
with the papillae of other birds such as the chicken or the starling. There
are only quantitative differences in the continuous morphological gradients
(such as hair cell height, stereovillar height) from neural to abneural,
and from the base to the apex of the papilla. Only few (about two in the
emu) afferent terminals and on average one efferent fiber contact each hair
cell. Along the abneural edge, there is a population of hair cells that
lack afferent innervation (short hair cells), suggesting that their
function must lie in the papilla itself. There is thus a general pattern in
the structures of the avian basilar papilla. In detail, however, a number
of primitive characters were observed in the emu, as compared to advanced
birds such as the starling and the barn owl. The hair cells are very
densely packed and comparatively tall (up to 40 microm in the apex). This
anatomy correlates well with the good lower-frequency hearing (see K oppl
and Manley, J. Acoust. Soc. Am. 101 (1997) 1574 1584). The afferent nerve
fibers contacting the hair cells within the basilar papilla are rather
thick, and there are a large number of afferent fibers that contact more
than one hair cell. The zone of hair cells without afferent innervation
(short hair cells) along the abneural edge of the basilar papilla is rather
narrow in the emu.
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