Abstract:
The tongue body of Rhea americana is triangular
and partially pigmented with each caudo-lateral
margin displaying a round, sub-divided lingual papilla. The
tongue root is a smooth, non-pigmented tract of mucosa.
The tongue body is supported by the paraglossum and
distal half of the rostral projection of the basihyal (RPB),
and the tongue root by the proximal half of the RPB, body
of the basihyal and proximal ceratobranchials. An urohyal
is absent; however, peculiar to R. americana, the caudal
margin of the cricoid body displays a median projection,
which may represent the remnant of the urohyal incorporated
into the cricoid. The laryngeal mound is less elevated,
the arytenoid cartilages are smaller than in other ratites,
and the caudal margin displays pharyngeal papillae that
vary in shape and number. The unique morphology of the
lingual skeleton and its positioning within the tongue of
R. americana, the rostral insertion of the M. ceratoglossus,
the absence of the urohyal (enhanced ventroflexion) and
the caudal positioning and mobile attachment of the ensheathed
basihyal to the paraglossum would appear to
allow independent movement of the tongue body relative to
the hyobranchial apparatus. Additionally, the deeply
indented base and rostral oval opening in the paraglossum
limits the length of cartilage present in the midline of the
tongue body. This may allow the tongue the necessary
flexibility for the lingual papillae to clean the choana. The
cleaning action of the tongue would occur simultaneously
with the previously described role of this organ and associated
structures during feeding. Thus, the so-called
reduced, ancestral tongue of R. americana may be structurally
and functionally more complex than previously
believed.
