Notes on the nasal tract complex of the Boutu, Inia
(De Blainville,
geoffrensis
1817) (Cetacea, Platanistidae)
by
E.J. Schenkkan
Zoological Laboratory, University of Amsterdam,
Abstract
of the
anatomy
Boutu has been
The
nasal
of three
passage
of the
specimens
studied.
various
diverticula
appear
aberrant
be
from
The
vestibular
enormous
the
diverticulum.
the total
blowhole,
covered
The
airsac
system
Except
dorsal
and rostral
strikingly symmetrical
for
maxillary
this somewhat
by
has
caudal
region
to the
caudal
area
one
to
orbits is
dome-shaped airsac system.
aspects
as
into
developed
a narrow
are
of the
also the
vestibular
system
here,
2277)
rostral
developed,
air
Accessory
ticula
are
of
parts
parts
sacs
broad,
the
nasofrontal
tubular
are
and
lacking
are
but their
diverticula
and
the
small.
relatively
bony
illary
filled
with
bones when the former
dorsal
swellings
frontal
the
for
the
of the
lian characteristics
was
not
that
The
curiosity.
and
study
of
only
in
morphology
those
of
of
a
several
of
the
Ray
seventeenth
great
the
Major
species,
with
the
Por-
1758)
and
Tyson
of
one
the
first
anatomical
cetacean,
"An
account
porpess",
John
Ray
scription
to
of the nasal
provide
a
of
the
studies
dissection
(1671) included
apparatus
functional
a
the
larynx
was
on
a
of
a
brief de-
in which he tried
interpretation
of
the features. He noted that the trachea
and
It
elongated,
some
was
of
short
terminating
in
&
naso-
cavity
conjecture,
neither
find
mammillares".
other papers
more
appeared,
Gruhl
1873),
(1930,
1919),
&
Young
been known
could
cetaceans
Schulte
a
Galambos
since
produce
used
as
(1940,
(1958)
sensitivity
classical
and
by bats,
1941),
see
Dijkgraaf
(1943)
dolphins
to
led
sounds
to
the
1947),
might
exist
high frequency
elegantly
folding
a
a
for emission and
sounds.
In
demonstrated
Bottle-nosed
of
high
to
that in
perception
1961, Norris
echolocation
Dolphin,
and
about
assumption
similar mechanism
cetaceans
discovery
e.g. Griffin &
with observations
together
of
sounds
perceive
that
bats
and
times that
frequency (Fraser,
in
(1888),
Beddard
(1918)
communicative meaning. The
of echolocation
the
Von
1911),
e.g.
(1879),
Carlsson
(1885),
Kernan &
concern-
published,
were
Beauregard
Murie
Hanke (1914)
(1911),
Watson
Hunter
e.g.
(1848),
Detailed data
1934).
species
(1867),
see
Sibson
(1826),
dealing
detailed studies of
(1934).
had
Griffin
(1680).
In
could
Benham (1901), Le Danois (1910,
having
e.g.
Baer
1871,
Pouchet
Huber
(1672)
two
tending
narrow
[Ray]
I
processus
have
region
Von
Burmeister
(1915,
Harbour
or
but
I
as
brain
anatomy,
uncommon
anatomy,
dealing
reports
no
two
and
two
of the
section
long
a
time, amongst
Huber
the
of
nor
ing
not
variety
the
nerves
and
in
proliferation
of
Common
(1671),
beyond
grew
phocoena (Linnaeus,
Phocoena
poise,
great
demonstration
Man but
resulted
interest
zoological
mamma-
and whales, but it
until the last decades of the
century
mere
dolphins
of the
[caudal
smelling,
opening
cetacean
(1870,
in
of
Since that
(1787),
aware
Ray
having
premax-
INTRODUCTION
were
brain
use
though
REVIEW AND
ancient Greeks
skull,
nasal plugs];
c.q.
airsacs], having
the facial
The
spout
nares.
snout;
diverticula
with
HISTORICAL
the
towards
tending
a
nares are
deflated.
are
the
[premaxillary diverticula];
olfactory
nearly completely
of
an
found
bony
blind holes
beneath it
diver-
premaxillary
lumina rostral to the
well
are
he
above the valve that stops the nostrils [now called
towards
caudal
level
vestibular
passage.
The
the
observed "six
four
out-let;
of the
lining
flesh"
above
From
the end like
at
distally,
the apex of the laryngeal
"glandulous
(1671:
More
are
of the nasal
deeper parts
a
those
described for other Platanistidae.
above
sphincter
"a nob
(: 2276)
fashioned Ewer".
and
to
he called
what
old
The
The Netherlands
et
al.
by
Tursiops
of
most
blindtrun-
276
E.
catus
found
increased,
quency
Caldwell
interest
in
structures
an
anisms involved in
modulation,
of
morphology
NASAL TRACT OF INIA
fre-
Prescott
&
Beil
the
augmented
has
-
list of
high
Sutherland &
Evans,
facial
various
understand the mech-
to
attempt
of
Caldwell,
e.g.
phenomenon
the
in
see
and
(1966)
This
(1964).
sounds
produce
to
SCHENKKAN
From that time the
1821).
(Montagu,
species
J.
production, transmission,
the
and
emission,
of
perception
has
Purves (1954,
Purves
been
the
nasal passage
in order
the
Schevill
with
dealt
find the
to
perception
Fräser
by
de Haan
Utrecht
and
adjacent
struc-
and
emit-
(1972,
Norris
of
phology
the
nasal
is
its
1972,
that,
sounds
the
the
by
mor-
suborder
the
concerning
used
in
in
function
alleged
in
within the
tract
and
1973)
variation
great,
so
of
uniformity
(1971,
The
1975).
Odontoceti
species,
nasal tract have been under-
Schenkkan
various
the
this
phonatory
system is unlikely.
The
apparatus in the
Platanistidae has been dealt with
by the
extent
Purves
Wagler,
blainvillei
Mead
&
Lipotes
for
Hinton
while
1918;
preliminary
a
Pontoporia
1844);
Miller,
vexillifer
(1878),
Schenkkan
(1867),
1975)
some
Platanista
genus
d'Orbigny,
(1975) published
to
Anderson
the
(1972,
(Gervais
for
(1936)
for
(1973)
Burmeister
1830;
and
of
descriptions
Pilleri
&
(1972)
Mead
nasal
morphology of the
note
Inia
on
geoffrensis (De Blainville, 1817).
&
Lawrence
e.g.
(1969),
and
responsible
structures
sounds,
Moris
(1956),
(1956),
(1963),
transmitting, beaming
various
&
whilst others
by Fleischer (1973),
recently
of
sound
Purves & Van
monitoring,
ting
the
1960), Reysenbach
(1966),
explored
for
of
morphology
structures
tures
Mead
family
The
more
by
these
sounds.
of the
morphology
taken
and
(1969)
MATERIAL AND DESCRIPTION
Norris
al.
et
(1971).
Analysis
of sounds
and the
pattern of emission had been dealt with by Evans
&
Prescott
(1962),
that
echoes
that
(1967). It would
of
importance
the
the
reflected
are
Evans
character
from
the
In
Kamminga,
of
the
surface
mammals
terrestrial
most
sounds is located in the
through
laryngeal
mitted
since
laryngeal
air-filled
to
and
there is
since
they
the
cally
to
reflection
lacking,
many
In
of
modifications
Edgardo
Mondolfi,
taxonomie
A
2.
of
mechanism of
the various sounds
theories
have
as
at
energy
where
any
the
by
is
over
air-water
is
enable
to
the
such
phonation
and
is still in debate,
the
postulated.
In
conflicting theories, comparative
Van
of
this
kindly
cast was
3.
head
of
kind
very
albino
water.
staff,
Goethe University
As
usual in
at
Inia
view of these
on
the
dissection
left of the
most
most
midline.
other
Contrary
the
almost
was
made possible by
Dr.
M. Klima
Centre
to
less
in
nasal passage
the orifice
vestibule,
state is
Zoo
of
J.
W.
Frankfurt/Main.
concavity
the
a
that
geoffrensis
Prof.
odontocetes,
species,
the
downwards,
the
at
head
tract.
Dr. W. Gewalt.
by
was
of
the
16.936).
this
Duisburg
the apex of the head,
Exploring
sound
the
of
dissect the head
From
Morphological
and
contra-
in
hospitality
directed with its
studies
the
Inia
Tax-
of
ZMA
no.
to
well.
as
of
Museum)
me
Dissection of this specimen
found
for
Mondolfi
Institute
made from the nasal
offered for
his
Dr.
Pedro Trebbau of
the
to
allowed
died
unfortunately
kindly
and
specimen
C.
Dr.
by
(Zoölogisch
specimen
silicone
The
from
Venezuela,
Bree
deepfrozen
Zoology
as
the vibra-
of
Caracas,
Venezuela,
Bree
geoffrensis
Bree
van
Van
donated
emission of
site
H.
University of Amsterdam (coll.
and
found in
surrounding
consisted of:
dissect the head.
me to
Caracas,
are
mammals, though special
to
J.
studies.
geoffrensis,
the
folds could subas
P.
mam-
cords
structures
concerning
been
there
vocal
phonation,
required
are
aquatic
by
air,
in
Dr.
complete
trans-
emitted
as
to
aryepiglottic
or
easily
surrounding
water
laryngeal
tions to be transmitted
sources
of
be transmitted economi-
the
other terrestrial
dicting
passed
inforcement
sounds
cetaceans
other
the
useless
are
cannot
the function
The
to
surrounding
thyroarytenoid
serve
air is
change in density
large
Airborne
99%
interface.
of
source
vibrations
are
for
cavities
terrestrial mammals
mals
The
structures
thence
no
path.
sound
by
onomie
the air and
resonance
the
study
head of Inia
preserved
borrowed
allowed
larynx where
structures.
formalin
of
comm.).
pers.
A
seem
various structures has been underestimated (Van
der Ree,
The material for the present
1.
& Evans
(1966) and Norris
Caldwell &
Caldwell,
what is
a
slit
is
caudal direction.
from the blowhole
slightly
of which in
completely
found in
crescentic
widens
lumen
the blowhole is
slightly disposed
filled with
to
its
the
form
resting
lips
of
BIJDRAGEN
Fig.
1. Dorsal
position
and
aspect
shape
of the
skull
of
of the vestibular
Inia
TOT
DE
DIERKUNDE, 46
geoffrensis (Zoological
system
by
means
of
a
(2)
Museum
mounted
-
277
1977
Amsterdam
silicone
cast
of the
coll.
no.
nasal
16.936) demonstrating
passage.
Photograph:
S.
the
van
Mechelen.
CSM
orbit;
=
supramaxillary
PM
=
crest; F
premaxillary bone;
=
frontal
SVL
=
bone;
FM
=
foramen
left vestibular sac; SVR
=
magnum;
right
M
=
vestibular
maxillary bone;
sac.
O
=
occipital bone;
OR
=
278
E.
the
blowhole.
over
passes
equal
in
After
blubber
In
the rostral
density and
removal
of
in
an
This muscle
ment.
the
In
skin
SCHENKKAN
the
rigid
and
more
Inia both
lips
NASAL TRACT OF INIA
sacs
and
thin
symmetrical
only
most
is
rostral
layer,
to
In
is extended
of the
Fig.
2.
Rostral
vestibular
BL
=
and
right
enormously,
deeper
muscle
the
layers
of the
aspect
of
the
system. Photograph:
blowhole;
M
=
covering the whole
extends
even
vestibular diverticulum
skull
van
maxillary bone;
to
and
the
nasal
mounted
cast
can
at
the
of
right
=
It
completely
anterior
the left side of the head, whilst
the
horizontally
&
Purves,
recognized
through
vestibule
situated
as
slit
in
1973).
being
its
a
mesial
Nevertheless
an
extension of
In
as
in
fig.
Inia,
Mead (1975)
1, demonstrating
the
mentioned
symmetrical
a
vestibular
orientation
Mechelen.
PM
the
side.
complexly trabeculated,
situated
with
(Schenkkan
still be
that
the lateral wall of the vestibule.
maxillonasalis
rostrally
same
S.
right
it
area
is
sac
complex, since
more
enormous,
the vestibule
corner
is
component
narrow,
Pontoporia,
an
communicating
the vestibular
covers
diverticula.
Schenkkan,
breviceps (De Blainville,
Kogia
situation
vestibular
possesses
arrange-
that controls the blow-
hole region, is very thin and
the
1838)
of
(see
lateral extensions of the lateral walls of
the vestibule. In
layer
the
are
midline
in odontocetes the vestibular air
1972). However,
are
the
crossing
passage
observed.
was
maxillonasalis muscle
almost
-
odontocetes
blowhole,
the
of the
layer
found lying
lip.
overlap
no
around
just
superficial
other
most
of the blowhole is
posterior lip
J.
premaxillary bone; SVL
=
left vestibular sac; SVR
=
right
vestibular
sac.
of the
BIJDRAGEN
system similar
to
that
found in
I
species
vestibular
right
this. At
confirm
cannot
does
sac
first
seem
not
to
is
of this
the
sight,
be
DE DIERKUNDE, 46
How-
Pontoporia.
from my dissection of the specimens
ever,
TOT
only
an
extension of the lateral wall of the vestibule, but
also
an
entire
its
over
Rostrad
airsac
and
vestibular
by
specimens
of the
vestibule,
somewhat
slopes
slit
it
tissue
of
lip-like
a
vestibular
sac
by
about
a
this
1
extension of
connection. No
lumina of left and
the
itself reaches
right
to
vestibular
system
right
seems
of the
sacs
above
vestibular
The
BL
3.
=
be
due
to
sac
across
left
one.
seem to
of
the
In
sacs
the
level
causes
the
slightly
rostroventral
as
is
Inia
developed
wall of the
of
vestibular
the
both
however,
and the
vestibule in
orifices
to
Lateral
aspect
of the silicone
=
cast
mounted
left vestibular sac; SVR
of
left
and
the
the
orbits;
direction
somewhat
are
odontocetes,
a
total
whole
and
slopes
3).
(fig.
is
right
(fig. 2).
area
covers
dome-shaped
in
rostral
there
The
wrinkled,
indicating its
the
bony
as
level of the
a
In
nares.
the
of the
crests.
dition found in
of this
to
slit-like
found, just
ligaments which
nor-
from the caudomesial border of the
laterally
maxillary bones towards
These
diverticula
expanded,
contrary
Pontoporia.
diverticulum,
partly
septum
caudal wall
the blowhole
to
nuchal
wall
flattened tube
the nasofrontal diverticula is
to
mally stretch
what
its
nasal
vestibule, the
rostrocaudally
dividing
In
I
Inia,
found
the
air
are
to
some-
the
con-
in
the dorsal
a
transverse
sac
into
two
compartments lying behind each other. A similar
condition
though
far
more
described for Phocoena
developed
has
been
phocoena (see Schenkkan,
1973).
this confluence.
dorsal aspect of the whole vestibular
blowhole; SVL
the
to
runs
caudal extension
could
midline and sup-
normally found
the
to
somewhat
ventrally
of
of the
dorsal
area
in
orifice
melon.
outgrowth
an
be well
of the rostral
protrusion
just
confluence
,
vestibular
Fig.
to
vestibular
pression
or
the
level
nearly
is
the
Kogia
system
system
the
about 3
sac
the
Mead's
though
in the communication
sac
vestibular
passage
be traced.
In
vestibular
The
in
to
the
contrary
Furthermore,
symmetrical
fairly
difference
slight
Deep
and
separation
1).
extensibility.
strand
thick
cm
(fig.
walls of the airsac
system
pene-
gristly
is
maxillary
ventrally
through which it
is bordered dorsally
left
wall
the base of the extension.
corner
The
rostrad of this
the
adult
rostral
symmetrical,
surprisingly
aspect
279
1977
-
observation
the dorsal wall of the left vestib-
through
sac
ventrally
cm
In
its
becomes continuous with the left
sac.
connective
The
at
cm
left
arrangement
trates
of
the
to
surprisingly
ular
width.
about 5
measures
of
extension
enormous
(2)
on
=
the
right
Rostral parts
area
same
skull
as
in
vestibular sac; V
fig.
=
are
1. Photograph:
vestibule.
tubular and
S.
van
relatively
Mechelen
small.
280
E. J.
4.
Fig.
BLi
=
=
of the
Deep aspect
nasofrontal
sac.
blowhole
caudal
ligament;
section
measuring about
the nasal system.
like
the
In
a
=
extensions.
cm
premaxillary
completely by
=
in length
albino
Inia
be
be
on
OF INIA
geoffrensis. Strips
of
paper
As
contrary
the
expected,
lack
premaxillary
bones lateral
to
air
over
the
in
no
to
nasal
lateral
sacs
lipare
illary bones (fig. 4), just
swellings
plug muscle;
is
the
indicating
are
passage
to the
left
also
found
Although
nasal
canal;
NP
=
nasal
plug;
SNC
less
conspic-
sac.
Pontoporia though
not
pertaining
it
has
the
to
be
to
nares
is
order
of the odontocetes,
striking
of the
ment
of
This
nasal
=
premaxillary
study
noted
of
the
that
the
symmetry of the skull of Inia in the region of the
those
nares.
in
cavities,
bony
nares.
NC
=
uous.
bones
of the premax-
rostrad of the
nasal
the parts of
their lumen is occluded nearly
the dorsal
=
of nasofrontal sac; SPM
both sides
configuration
traced,
bulbous and
The
NASAL TRACT
crest; MNP
rostral section
In all specimens I dissected
broad and extend also
deflated state
an
supramaxillary
symmetrical
findings.
appear to
relatively
CSM
could
sacs
Mead's (1975)
plugs
IVi
of
system
-
J. Herforth.
of nasofrontal sac; SNR
and also showing
accessory
nasal
Photograph:
SCHENKKAN
of the
complete
that
the
and
right
side
left side
nares
to
where
are
the
of the
a
left.
(fig.
rostrum
the
whole
sub-
specifically
always
causing
skull from above
the axis
in
unique
larger
slight
displace-
Observing
1), it
does
not
the
than
the
is obvious
lie
in
the
TOT DE DIERKUNDE, 46
BIJDRAGEN
the foramen
plane with
same
continuous
not
column
(see
with
also
the
in that it is
magnum
axis
of
the
vertebral
Slijper, 1936).
(2)
air
passing
1973).
this
in
mechanism and
debate and
possible
main
site
is
opinion
divided
in
generated
are
the
is
two
between
Certain authors
systems.
that all sounds
of sound production
maintain
is
Norris
(1962),
Mead
(1975).
source
(1964),
Norris &
Others
consider
being
as
laryngeal,
be
might possibly
tures
Evans
involved
tion of various sounds that have
meaning
Lilly
or
emotional
are
Purves
(1961),
Schenkkan &
in the
(1973)
struc-
communicative
a
see
Schenkkan
e.g.
(1973),
Purves &
and
main
produc-
expressions,
(1966),
Purves
the
other
though
and
(1967)
least
at
Pilleri
(1973).
Norris et al.
(1971) concluded
the left nasal
at
echolocation,
nasal
plug.
tidae
and
bous
structures
the
at
Since
in
Purves
Purves
(1973)
clicks,
lateral
Physeteridae,
used
Hyperoodon-
nasal
lateral
Pilleri
(1973),
and Schenkkan
were
lip of the right
lacking
&
chirps
and
plug,
Platanistidae the
sions,
that
plugs
bul-
are
flap-like
operating.
able
that
as
it
Moreover,
when
lateral lip-like
act
its
the
nasal
structures
one-way
valves
plugs
be
to
apex
(Schenkkan,
the
oscillations,
suitable for
that
site
where
that
by
1973).
of
apex
above
the
the
reflecting sounds that
be
might
involved.
of
of
are
transmitted
easily
acoustic
most
phonation
whole
sealing
The
all.
at
airsac
only
system
has
be
to
secondary function
a
a
a
in
transmitted from below
are
in
However,
sounds
opinion
my
rostral
in
is
significance
direction
overestimated.
Prevention of transmission of these sounds in the
direction of receiving
bulla,
meatus
etc.
structures
might
the
as
of
be
tympanic
equal
or
even
greater importance.
LITERATURE
the
ANDERSON,
1878.
J.,
comprising
Purves
is
the
to
these
larynx,
with the
nasal plugs
sealing function, though
relaxation
larynx
the
of the
level
mem-
within the
Moreover,
interfere
for
to
must
cella.
at
to Western
can
Text:
I—LXXXI,
1—29
rostrum
sounds
I,
BAER,
Anatomical
account
an
monograph of
highly
phonation, while sounds produced
its apex the emission of
at
of
way
is the
uniform
nasal passage
function
primary
expeditions
concluded
(1966)
diagonal
the
strikingly
not
site
the air. This
seated.
are
cetaceans.
does
reserve
phonation
&
found in Delphinidae
as
is
reason-
seated,
are
for
considered
large
a
that
(1972) thought
seems
of the
fit
plugs
mechanism of the
being
have
sealing
exten-
Schenkkan
least in these families another mechanism
at
be
not
which
whole order of
at
the
(Schenkkan,
also
(1975)
only remaining possibility
structure
reflection
monitored
for
does
hypothesis
side
with
passage
to
by
membranes;
necessity for recycling
branes when the
The
nasal
Mead
either
on
of the
interfere
the
produced
be
may
edges
advantageous
minimize the
distal
most
of the nasal apparatus, e.g. Evans & Prescott
part
will
of
Moreover,
it
volume
The
the
along
mechanism
that
sounds
seated,
pletely
however,
DISCUSSION
281
1977
-
and
of the
in
Yunnan
researches:
zoological
results of the two
zoological
1868
and
1875;
the two cetacean genera, Platanista
vii—xxv,
XI1IA,
1
1—985,
XXVA,
map;
and
II. Plates: i— vi,
LXXVA,
a
and Or-
LXXVB,
pis.
i—xi,
(B. Quaritch, London).
K.
E.
1826.
VON,
Die
Nase
der
Cetaceen.
Isis,
Jena,
1826: 811—847.
be
Phonation and
traced.
avoids
great
sound path
Mead
so
discontinuity
emission
in
the
in
this
way
BEDDARD,
of the
density
that reflection is minimized.
(1975) concluded
from the
muscle fibres associated with the
based
discovery
diagonal
ban
of
mem-
—,
branes,
subserve
these
the
these
ities
airflow
with
ing
air
to
upwards
be
and
restricted
type of
these membranes
act
pressed
only
suitable
the
one-way
alongside
when
the
higher
To my
valves
the
plugs
of air
mind,
of two
prevent-
not
plugs
com-
W.
of
to the
of the
knowledge
(Physeter macrocephalus)
a
young
foetus. Ann. Dur-
VIII.
contributions to the
foetus.
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based
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upon
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an
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VIII—XI.
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An.
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additional
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BENHAM,
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BURMEISTER, G.,
nasal
are
his
1
Further
to
veloc-
quantities
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as
In
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permit
structures
needed for this
are
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of
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opinion
of
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the
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