A COMPARATIVE MORPHOLOGICAL STUDY ON
THE TONGUES OF MANATEE AND
DUGONG (SIRENIA)FUSAO YAMASAKI, SHUNRO KOMATSU
Department of Biology, Sapporo Medical College, Sapporo

AND

TOSHIRO KAMIYA*
Department of Anatomy, Faculty of Medicine, University of Tokyo, Tokyo

ABSTRACT

Tongues of two species of manatee, Trichechus senegalensis, and T. manatus, and of the dugong, Dugong dugon, were observed macro- and light microscopically. The tongue, with an anterior short free tip in both families, wasa slender, firm, very muscular structure set rather vertically but with adipose
tissues being rather rich in the posterior part. No circumvallate papillae,
sulcus terminalis, and foramen caecum could be seen on the dorsum. The
lingual apex was rounded in the manatee and truncated in the dugong. While
many digitiform, cuticular spines were present in the tip region, in dugongthey extended further posteriorly and were shaggier than in manatee. The
remainder of the dorsum of the manatee was quite smooth whereas that ofthe dugong had small elevations, some of which had a bunch of spines. A
pair of multifossulate swellings was present on both posterior margins withanother pair occurring on the posterior part of the side wall in the manatee.
In the dugong, two rows with pits could be seen on either of two regions corresponding to the dorsal swelling in the manatee. Similar pits were also
found in a group at the base of the lingual side wall. These structures on thedorsum of both manatee and dugong are homologous to each other, as arethose on the side wall. However, those on the dorsum and side wall may exhibit variations in the vallate and foliate papillae, respectively. Taste buds
were limited to the thin epithelia of the fossulae of the swelling in the manatee
and to the epithelia of the pits in the dugong. Mucous glands, though partially mixed ones, in the manatee and well developed serous glands in thedugong opened into the fossulae and pits, respectively. The posterior glandular portion contained well developed pure mucous glands. The lateral surfaces were studded with round, flat patches in the form of large-sized fungiform papillae, which may act as tactile organ.

* Present address:
Japan.

Anatomical Laborato'f)1, College of Jl.{edical Technology, University of Tsukuba, lbaraki 305,

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YAMASAKI, KOMATSU AND KAMIYAINTRODUCTION
The sirenian order is one of three major mammalian groups (along with cetaceans
and pinnipeds) that have adapted to living in water. There are two living sirenianfamilies; manatees (Trichechidae) and dugongs (Dugonidae). Trichechidae has
only one genus, and that genus is classified into three species; Trichechus manatus,
T. inunguis, and T. senegalensis. On the other hand, among Dugonidae, only one
species, Dugong dugon, now remains. As sirenians feed on water plants (being entirely
vegetarian) in shallow water, their digestive systems are interesting and differ considerably from those of cetaceans or pinnipeds. Not a few morphological observations have been made on the tongues of manatee or dugong (Rapp, 1857; Owen,
1868; Murie, 1870; Gmelin, 1892; Beddard, 1897; Weber, 1904; Gudernatsch,
1907, 1908, 1909; Sonntag, 1922; Aoki et al., 1938; Hill, 1945; Gohar, 1957; Nairet al., 1975; Husar, 1978). However, most of these descriptions excepting Gudernatsch's (1908, 1909) have been very brief and ambiguous, and comparative studies of manatee and dugong tongues have been very scarce. Since we have identified some differing morphological characteristics on the tongues between the two
families, the results are reported here and offered as an addition to the knowledgeof sirenian tongues.
MATERIALS AND METHODS
Two tongues of the African manatee, Trichecus senegalensis, one of the West Indian
manatee, T. manatus, and three of the dugong, Dugong dugon, were used for this study(Table 1 ). The African manatees (body length 158 cm, male, specimen No. TS-1;
and 198 cm, male, TS-2), sent by boat from Africa in a frozen state, were given us
by the Ocean Research Institute of the University of Tokyo. The West Indian
manatee (body length 282 cm, male, TM- I) was provided by the Yomiuriland
Aquarium, Tokyo. One of the dugongs (138 cm, male, DD-1, collected in thePhilippines) was imported for scientific research by permission of the Philippine
Government, while the other two (204 cm, female, DD-2; and 254 cm, DD-3, collected in Indonesia) were provided by the Okinawa Expo Memorial Park Aquarium, Motobu, Ja pan. After dissection, the tongues of these animals were fixed with
10% formalin solution in our laboratory. Following gross anatomical observationsof the tongues, materials for histological observations were excised from several
parts of the tongues and were embedded in paraffin or celloidin. Sections madefrom these materials were stained with hematoxylin-eosin.
OBSERVATIONSGross anatomy
The tongues of the sirenians, both manatee and dugong, observed were firm andhard muscular structures. They were slender when viewed from the dorsal aspect(Figs 1 and 6), and were set rather vertically due to the narrowness of the space
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between the mandibular rami. There were no median sulcus, vallate papillae,
sulcus terminalis or foramen caecum on the dorsum. Since the anterior two-thirds,
which was elevated, was divisible from the posterior lower glandular portion, forconvenience sake we regarded the anterior and the prosterior as the body and theroot of the tongue, respectively, in this study. Measurements of the tongues areshown in the following table.
TABLE 1.

Specimens

MEASUREMENTS OF THE TONGUES OF MANATEESAND DUGONGS OBSERVED
Sex

Length*(cm)

Breadth**(cm)

Thickness***
(cm)

158
198

male
male

14
15

3
3

2.5
2.5

282

male

19

4

4

138
204
254

male
femalefemale

10.5
13
16

2.7
3.5
4

2.5
3.5
4.2

Body length(cm)

Trichechus senegalensis

TS-1
TS-2
Trichechus manatus

TM-1
Dugong dugon

DD-1
DD-2
DD-3

* Whole length from the lingual apex to the base of the epiglottis.
** The widest portion at the posterior of the lingual body.
*** The thickest portion from the floor of the mouth at the mid-part of the body.

The anterior free tip of the tongue, without frenulum, was short, about 1 cm
to 1.5 cm in length, and the tongue, ventrally, was extensively attached to the floorof the mouth, indicating that the sirenian tongue may possesses only limited mobility. The tip of the tongue of the manatee was rounded (Fig. 1) while that of thedugong was truncated (Fig. 6). The tongue of sirenians thickened progressively
from the anterior to the posterior part of the body, and thinned in the posterior
glandular portion, the lingual root (Figs 2 and 7). The mid-part of the dorsum of the
body was considerably convex, both lengthwise and transversely in the dorsal direction. In the dugong, a wide longitudinal elevation of about one-third of the lingual width was seen on the mid-part of the dorsum, thus forming lateral strips oneither side. In the young dugong, DD-1, the lateral strips were not so marked.
The anterior dorsum in the African manatee, approximately 2 cm in extent fromthe apex, was covered with many hard, digitiform, cuticular spines, each about 2
mm in length and 0.2 mm in thickness, which were anteriorly directed along thecornified hard anterior margin (Fig. 1). Small amounts of fine, soft spines wereseen extending almost to the posterior half of the lateral margin. In the West Indian manatee, the anterior margin was rather uneven in appearance, and a few
spines, 1 mm or less in length, were seen in several parts along the margin. In
both species of the manatee, the dorsum, excluding the anterior spine covered region, was quite smooth, both to touch and the naked eye, and was devoid of thepapillous processes seen in other land mammalian tongues. In the dugong, the anterior dorsum of the tongue, about 1.5 cm in extent from the apex, was thickly covSci. Rep. Whales Res. Inst.,

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YAMASAKI, KOMATSU AND KAMIYA

ered with hard spines quite closely resembling those in the manatee, though far
shaggier (Fig. 6). Anterior spines extended to the ventral side of the free tip, being about 5 mm in breadth and having a clear border. Smaller and softer spines
than those in the apex region occurred on the anterior fourth of the mid-part andon lateral strips, except at the middle longitudinal elevation. In the case of theyoung dugong, DD-1, they extended far posteriorly covering almost all of the dorsal surface of the body and were shaggier than those in the apex region. Spines
in the dugong were stained dark brown in color, probably by the juices of seaweed.
In the dugong, the lingual dorsum had small elevations, 0.2 to 1 mm in diameter,with superficial minute unevenness, especially remarkable along the mid-line area
except for the tip region. A bunch of digitiform spines grew on the elevations (Fig.
8), showing the patterns of what Gohar in 195 7 called "papillae calici-penicilliformes".
In the manatee, specific areas with many fossulae forming pairs were present nearboth posterior lateral margins of the dorsum (Figs 1, 3 and 4). There were roughly
25 to 30 rather large fossulae in the area, each area being clearly distinguishable
from the neighborhood. These areas formed remarkable swellings, multifossulate
swellings, in the African manatee (Figs 1, 3 and 11) but not such remarkable ones in
the West Indian manatee (Fig. 4). The swellings, with gradual thinning anteriorly,
were slightly opened anteriorly. The swellings in the African manatee were approximately 2 cm long and 0.7 cm wide in the posterior part; was 2.5 cm long and
0.8 cm wide, in TS-1 and TS-2, respectively; and was about 2 cm long and 0.8 cm
wide in the West Indian species. Another multifossulate swelling was present oneither lateral wall, in the anterodorsal region of the palatoglossal arch (Figs 2 and 5).
This lateral swelling was about 0.8 cm across in TS-1, and 1 cm in TS-2, and had
about six to eight fossulae*. Since the swelling of this area was rather more poorly developed than that of the dorsal swelling, and since a part of the lateral swellingintermingled with the patches which are mentioned later, the boundary of the lateral swelling was rather inconspicous compared with that of the dorsal swelling.
Some fossulae resembling those of the swellings were seen at the lingual margin between the dorsal and lateral swellings. Therefore, at first sight it appeared thatboth the dorsal and lateral swellings were fused each together into one continuous
large swelling**. Fossulae at the swellings were rather elliptic, about 1 mm inminor and 2 mm in major axes, and were arranged in a rather parallel mannerin the African manatee. Fossulae located at the posterior part of the dorsal swelling in the West Indian manatee were rather shallow and composed of several minuteglandular openings. Many small glandular openings were observable on the dorsum
from the region between the middle part of both dorsal swellings to the epiglottis.
In the case of African manatee, TS-2, both sides of the dorsum of the root wereslightly swollen with rather large openings being observable on their surface.

* In the West Indian manatee the regions on both sides on which the lateral swellings may be present
were not observable, because they were excoriated.
** We described both swellings, dorsal and lateral, as a single swelling in a previous paper (Yamasaki
et al., 1980).
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On the other hand, in the dugong tongue, two rows with deep pits (three onboth sides in DD-1; right, six, and left, seven in DD-2; three on both sides in DD3) were present near both posterior lateral margins which correspond to the posterolateral region of the dorsal swelling in the manatee (Figs 6 and 9). The regions withthe dorsal pits were not elevated. The pits were round, about 1 mm in diameter.
Arranged longitudinally, they opened slightly anteriorly with a separation of about
3 to 4 mm. Small projections could be seen in some pits. Glandular openings,
smaller than those of the pits and surrounded by small elevations, were observedon the dorsum from the posteriormost pit to the epiglottis. Three to seven pits,
the lateral pits, (seven on the right and six on the left in DD-1; six on the right in
DD-2*; three on either side in DD-3) resembling the dorsal pits, were present ina group, a little nearer the dorsal surface adjacent to the anterior region of the palatoglossal arch (Figs 7 and 9). This region was confined to within about 1 cm orless and was not elevated.
In both, manatee and dugong, 20 to 25 round, fiat conspicuous patches wereseen extending on both sides from about the anterior one-fifth of the tongue almost
to the palatoglossal arch in the manatee (Fig. 2), and from the mid-part to near
the arch in the dugong (Fig. 7). The patches were rather white in color in the
fixed state, 1 to 3 mm in diameter, and slightly elevated. One or more small
glandular openings were seen on the surface of some of these patches. Those located at the posterior intermingled regionally with the lateral swelling in the African
manatee, and the lateral pits in the dugong. Small glandular openings were seenin the ventral region of these patches, being particularly abundant on the posterior
part.

Histology
Though the sirenian tongues observed were extremely muscular, adipose tissues was rich in muscular tissues in the posterior area. Superior longitudinal muscle bundles were rather well developed immediately subjacent to the mucous membrane on the dorsum except in the posterior glandular portion. The epithelium of
the dorsum at the spiny apex region was thick, approximately 2 mm or more, but
gradually thinned toward the rear. The epithelium of the dorsum along the midline region of the manatee was relatively thin, with the epithelium becoming thickat the lingual lateral margin. The thickness of the epithelium of the side wall was
about 1 mm. A superficial layer, about 15 µm, of the epithelium, excluding therear part, was cornified. Epithelia of the dorsum and side wall of the dugong were
not thick when compared with those of the manatee. The spines ofsirenians, whichwere strongly cornified filiform papillae, consisted of a cornified superficial epithelium without a conical elevation of the tunica propria. All spines located posterior of the dorsum were thinner than those in the apex region but were almost thesame in histological appearance.
The submucosa beneath the multifossulate swellings in the manatee was oc-* Pits on the left could not be counted, because this area was excoriated.
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cupied by a lobulated gland mass mostly composed of mucous glands (Figs 11 -14).
In regions with fossulae, mixed glands which were usually present often opened directly into the fossulae at the relatively upper part (Figs 12 and 14). The glandmasses at the mid-part of the dorsal swelling were approximately 7 mm and 8 mmdeep in the African manatee and West Indian species, respectively. The gland massof the lateral swelling (Figs 15 and 16) reached about half the depth (TS-2) or less(TS-1) of that of the dorsal swelling. The gland masses of both the dorsal and lateralswellings fused with each other. The fossulae were approximately 1 mm in depth.
The inside wall of the fossula was covered with stratified squamous epithelium of
about 50 µm in thickness, without cornification. Secondary papillae were rather
poorly developed in this part. This epithelium contained pale flask-shaped structures or irregularly arranged cell masses with occupied almost the total thicknessof the epithelium (Fig. 12). These were undoubtedly degenerated taste buds, although they were not clearly confirmed due to their poor condition. Well developed pure mucous glands about 6 mm in depth were present from the front of themultifossulate area to the rear. This mucous gland field extended from the anterior part of the palatoglossal arch to the ventral region of the side wall of the tongue.
Capacious ducts were seen in places in the glandular tissues of the tongue (Figs 12
and 13).
On the other hand, in the dugong, pits, both dorsal (Fig. 17) and lateral (Fig.
18), were approximately 3 mm in depth, and surrounded by well developed lobulated pure serous gland masses, clearly distinguishable from the neighboring welldeveloped pure mucous glands (Fig. 17). Wide lumens of gland ducts were observed in these glandular tissues. Since the serous gland mass was fused .to theadjacent gland mass, large serous gland areas existed beneath the pits. The glandmass at the dorsum was approximately 14 mm in depth, and that at the side wall
was about 10 mm deep. Serous glands opened into the pits and the neighboring
mucous glands opened directly onto the dorsum. Some of pits had small projections protruding from their bottoms or walls (Figs 17 and 18). The epithelia of thepits, in which taste buds could be seen, were thin, being about 50 µm in thickness.
Taste buds were found grouped together in some places, especially in the lateralpits (Figs 18 and 19). There seemed to be a larger number of taste buds in thepits of the dugong than in the fossulae of the manatee.
Sections of the round patches on the lateral surfaces of the tongues of manatee(Fig. 20) and dugong (Fig. 21) showed a thinning of the epithelium of approximately 100 to 200 µm. Secondary papillae at the patches were relatively short witha superficial 12 to 20 µm of their epithelium having a tendency towards cornification. The lamina propria of this region contained relatively abundant thick nerve
fiber bundles (Fig. 22). No taste buds were present at the patches. Mucous
glands, comparatively poorly developed in relation to those at the rear part of thedorsum, opened on the surface of some of the patches.
The mucous glands of the rear part of the tongue extended to the palate andpharynx. Those in the dugong were well developed when compared with thosein the manatee. Dugong glands also extended down almost to the end of theSci. Rep. Whales Res. Inst.,
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esophagus. Condensations of lymphoid tissue could not be observed at the lingual
root except in one case, African manatee, TS-2, which had some lymphatic nodulelike structures with crypts.
DISCUSSION

The sirenian tongue is difficult to divide strictly into two portions, the body andthe root, due to the lack of a row of vallate papillae, sulcus terminalis, and a traceof foramen caecum, which are features seen at the border between the two portions
in many land mammalian tongues. Therefore, the whole length of the tongue wasmeasured from the apex to the base of the epiglottis. However, data reported byformer investigators have often been unclear as to the posterior measuring point.
Measuring points are necessary in the estimation of data showing the length of
tongues such as those of sirenians, since they have no border marks between the
body and the root as in cetacean tongues (Yamasaki et al., 1976a, 1976b, 1978a,1978b).
There are some ambiguities among previous descriptions on the manatee anddugong tongues. However, the characteristics of the sirenian tongue observed were
1) comparative smallness in relation to body size, 2) slenderness and vertical thickness, 3) absence of sulci on the dorsum, 4) existence of hard, digitiform, cuticularspines in the apex region, 5) existence of large-sized patches on the side wall, 6)presence of peculiar gustatory organs, varied types of foliate and vallate papillae.
Anatomical differences between the two families are summarized and shown intable 2. Items in the table will be compared and discussed.
TABLE 2.

ANATOMICAL DIFFERENCES BETWEEN MANATEE
AND DUGONG TONGUES
manatee

I.
2.

Apex
Spines3.

Dorsum4.

Gustatory organ

5.

Glands of thegustatory organ

round
existing in the apex region
onlysmooth, devoid of papillous
projections
forming dorsal and lateralmultifossulate swellings
mucous, partially mixed

dugongtruncate
extending posteriorly on the bodyof the tongue
full of small elevations with spines
having several pits on dorsum andside wall, forming no swellings
serous, well developed

The outline of the apex of the manatee tongue is rounded. That of the dugong is truncated, but the bifid tip in the dugong as reported by Hill (1945) could
not be observed. Since the apex in the young dugong is round as in the manatee,
age and individual differences may be related to its outline. In young dugong,
Gohar (1957) observed that the cornified tip of the tongue is smooth but that withadvancement in age it develops stiff bristles and becomes rasp-like in appearance.
Our observations on a young dugong, whose spines at the tip were very short, is inapproximate agreement with his descriptions. Drawings of a conspicuous horny
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YAMASAKI, KOMATSU AND KAMIYA

process at the apex pointing anteriad in the dugong tongue were done by Sonntag(1922) and Aoki et al. (1938), and the process was described by the latter.
However, we could not locate such a process at the tip region in the tongues of either family.
One of the great differences between the two families is the appearance of thedorsum. In the dugong, small epithelial elevations, each with a bunch of spines,
spread over the dorsum in contrast with the smoothness of the dorsum of the manatee. Gohar (1957) made very detailed descriptions of the appearance of the dorsum of the tongue of the Red Sea dugong. He stated that no typical circumvallate papillae could be seen, and proposed to call the special type of papillae observed, a bunch of spines on the elevation, "papillae calici-penicilliformes". He looked
upon them as a modified form of the circumvallate papillae. We cannot agree
that the structure composed of special papillae is a modification of the circumvallate papillae, but we assume that it may be a specially arranged filiform papilla,
because of its form, distribution, number and histological features. Vallate papillae have been reported on the posterior part of the dorsum of the manatee by several investigators; Rapp (1857)* in Manatus latirostris, Murie (1870)* in M. americanus,
Gmelin, (1892) in M. latirostris, Weber (1904), species unclear. In the dugong,clustered vallate papillae and rudimentary ones have been reported by Sonntag(1922) and Hill (1945)**, respectively. However, Gudernatsch (1909) observedthat these papillae were absent in sirenian tongues, and we also could not locate
such papilla in our specimens. Gudernatsch (1909) reported "Spiegeln" on thedorsum resembling those on the side wall of M. latirostris and he considered them
to be fungiform papillae. However, in our specimens we could not find such
structures on the dorsum, except for the side wall.
The most characteristic feature of the sirenian tongue is the presence of
peculiar gustatory organs, a multifossulate swelling in the manatee and pits in thedugong, with notable differences in the organs being marked between the two families. Several interpretations have been made by former investigators and there
has been confusioh in terminology among them, especially on the organs of themanatee.
The structures that seem to indicate a dorsal swelling in manatee judging fromthe descriptions, drawings or figures are:
1. a sieve and tonsil-like plate by Rapp (1857) in M. latirostris
2. many fossulate-papillae by Owen (1868)***, species unclear
3. a double set of circumvallate glands by Murie (1870) in M. americanus
4. an anterior tonsil by Gmelin (1892) in M. latirostris (with a drawing)
those seemingly indicating a lateral swelling are:*Rapp (1857) and Murie (1870) might have considered even the patches on the side wall as vallate
papillae, since they indicated that the structures extended to the anterior third of the tongue. This distribution almost corresponds to that of the patches of our specimens.
Hill (1945) reported another group of vallate papillae just anterior to the foremost group in the piton the side wall in the dugong.
Owen (1868) described the structures as extending to the anterior third of the tongue.

**

***

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a simple lateral gustatory organ by Gmelin (1892) in lvl. latirostris (witha drawing)
2. a large papillary plate by Weber (1904), species unclear
and those probably indicating a continual single swelling, dorsal and lateral, are:
1. a large patch of circumvallate papillae (Mayer's organ)* by Beddard(1897) in lvl. inunguis (with drawings)
2. a compact glandular apparatus with gustatory pits by Gudernatsch (1909)
in lvl. latirostris (with photographs)
3. a large cushion with numerous fissures (lateral organ)** by Sonntag(1922) in lvl. americanus (with a drawing)
However, the descriptions of the pits in the dugong by former investigators
have been clearer than those on the swelling in the manatee, though the pits havebeen written of with various terms: Gudernatsch (1907, 1908), on the dorsal andlateral pits (with photographs); Aoki et al. (1938), dorsal and lateral (with drawings); Hill (1945), dorsal and lateral; Gohar (1957), lateral only (with a drawing);
Nair et al. (1975), lateral only; Husar (1978) dorsal only. Although detailed
observations were made on the gustatory organs in both manatee and dugong
by Gudernatsch (1908, 1909), for some reason, no investigators have referred tohis articles.
Undoubtedly the multifossulate swelling and pits are a variation of the gustatory organs*** formed by lingual papillae. However, it is difficult to conclude
whether they correspond to the vallate or foliate papillae, since neither animal has
these two kinds of papillae, at the corresponding regions as seen in other land mammalian tongues. The classification of the lingual papillae is based on their formand distribution. Since the gustatory organs on the dorsum and on the side wallin sirenian tongues are quite similar to each other morphologically, it would be moreadvisable to clarify the organs by distribution rather than by form. The lateraland dorsal pits of the dugong are clearly distinguishable in their location. As thelateral swelling in the manatee is located in almost the same region as the lateralpits in the dugong, both structures may be considered homologous to each otheras indicated by Gudernatsch (1909). Some former investigators have stated thatstructures corresponding to the lateral swelling (Gmelin, 1892; Weber, 1904; Gudernatsch, 1909) and the lateral pits (Gudernatsch, 1908)**** were primitive typeof the foliate papillae. We agree that the structures belong to the foliate papillae,
but believe it advisable to consider them a varied type of foliate papillae rather than1.

* Mayer's organ is a structure with numerous fissures located on the lateral surface of the elephanttongue. As this structure was first described by Mayer in 1844, it has since been called Mayer's organ inhonor of its discoverer (Forbes, 1879). This structure in the elephant tongue consists of the foliate papillae
themselves (Shimizu et al., 1960). Therefore, the description by which Beddard (1897) regarded circumvallate papillae as Mayer's organ is inadequate.
** Although Sonntag's description is extremely ambiguous in the use of the term lateral organ, we
have judged from his drawing that the organ may have indicated a swelling.
*** Aoki et al. (1938) and Gohar (1957) considered the pits of the dugong as merely glandular openings.
**** Gudernatsch (1908) also used the term" remnants" for the structures.
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to label them a primitive type of foliate papillae variation. Gudernatsch (1909)
observed that the group of gustatory pits on the side wall (=lateral swelling) in themanatee extended to the dorsum, that is, he believed the pits on the dorsum ( =dorsal swelling) to be a continuation of those on the side wall. We, however, consider the dorsal swelling in the manatee to be an independent structure from thelateral swelling as is also true in the case of the dorsal pits in the dugong, and believethat the structures on the dorsum in both animals may be a variation of the vallate
papillae. In the case of the manatee, the organ is multifossulated and expanded,and swells upwards. In the dugong, on the other hand, the organ grows downwards, with each pit becoming deep instead of being multifossulated. In the manatee, when each swelling, dorsal and lateral, has become well developed with age,the swellings may fuse with each other, and may then be seen as a single continuous
large swelling as shown in Beddard's figure (1897).
There have been no descriptions concerning the existence of taste buds in themanatee, and only Gudernatsch reported numerous ones in the dorsal pits (1907)
and in the lateral ones (1908) in the dugong. However, though the number oftaste buds in the sirenians observed may not be as numerous as those of vegetarianland mammals, they are much more numerous than those in cetaceans (Komatsu
and Yamasaki, 1980).
The region with pits in dugong consists of a well developed serous gland mass,
while that of the swelling in the manatee is composed of a mass of mucous glands,
though partially mixed ones, in agreement with Gudernatsch's descriptions (1908,1909). In the region having taste buds in the fossulae, mixed glands are foundnear the upper part of the fossulae in manatee. Serous fluid may be useful in rinsing the fossula or pit having taste buds, particularly in the case of dugong, which
feed on sea grasses. It is possible that some enzymes contained in serous fluid mayturn the polysaccharide of sea grasses into the small molecules which stimulate thetaste buds. Gudernatsch (1909) considered that the manatee's gustatory organ
glands showed a far simpler grade of development than those in dugong, based on the
poorly developed serous glands in manatee, and stated that marked morphologicaldifferences of the gustatory organs between the animals might depend on some biological factors rather than on the difference in food habits. Since this is a very interesting problem and since adaptation for foods cannot be disregarded, further
studies are expected.
In the dugong, Gohar (1957) observed that mucous glands containing fewer
and smaller serous glands were present under the whole surface of the tongue except for the anterior tip. However, in our observations mucous glands were notpresent in the lingual body except on the lower part of the side wall, but were present at the root, and serous glands were limited to the pit region. Dugong glands,
in particular, are more well developed than those of manatee and extend down almost to the end of the esophagus.
The other characteristic external feature is the presence of patches studded on
the lateral surface of the sirenian tongue. Gudernatsch (1908, 1909) called thesestructures "Spiegeln" in the dugong and manatee, and regarded them as fungiSci. Rep. Whales Res. Inst.,
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form papillae. In the dugong, Gohar (1957) also described various sized fungiform papillae, whereas Hill (1945) stated that these were absent. We consider thepatches in sirenians to be large-sized fungiform papillae. Although they have notaste buds, it is supposed that the structures play the role of sensory organs, probably tactile organs.
Rapp (1857) reported tonsils, which were oval plates having numerous openings and showing a sieve-like appearance, on each side in the posterior part of the
tongue in M. latirostris. Gmelin (1892) showed anterior* and posterior tonsils in
his drawing of the same species. However, it is as yet uncertain whether or not
lingual tonsils are present in the sirenian tongue at the corresponding region since
only in one case of African manatee have structures which seem to be poorly developed lingual tonsils with crypts been seen.
ACKNOWLEDGMENTS
We are greatful to Doctors M. Nishiwaki, University of the Ryukyus, Naha,
Okinawa and T. Kasuya, Ocean Research Institute, University of Tokyo, for kindly
supplying the materials for this study. We wish to thank Doctors J. E. Reynolds
III, School of Marine and Atmospheric Science, University of Miami, K. Kubota,
Institute of Stomatognathic Science, Tokyo Medical and Dental University, andK. Takahashi, Department of Anatomy, Sapporo Medical College, who gave us
valuable suggestions and advice for our study. The techincal assistance of Mr S.
Ohtani, Risto-Technical Center, Sapporo Medical College, is also acknowledged.
REFERENCES
AOKI, B., S. TATEISHI, R. TANAKA and K. FuRuHATA, 1938. Anatomical notes on the dugong. Kagaku no
Taiwan (in Japanese), Lab. Comp. Morph. l\1ammal., Zoo[. Inst. Taihoku Imp. Univ., 5: 1-28.
BEDDARD, F. E., 1897. Notes upon the anatomy of a manatee (Manatus inunguis) lately living in the society's
garden. Proc. Zool. Soc., London, pp. 47-53.
FORBES, \V. A., 1879. On the anatomy of the African elephant (Elephas africanus Blum.). Proc. Zool. Soc.,
London, pp. 420-435.
GMELIN, W. 1892. Zur Morphologie der Papilla vallata und foliata. Arch. f. mikr. Anal., 40: 1-28.
Gm1AR, H.A.F., 1957. The Red Sea dugong. Publ. l\llarine Biol. Sta. Chardaqa, 9: 3-49.
GuDERNATSCH, ]. F., 1907. Untitled. Amer. Nat., 41: 665.
GuDERNATSCH, J. F., 1908. Zur Anatomie und Histologie des Verdauungstraktes von Halicore dugong Erxl.
Morph. ]b., 37: 586-613.
GuDERNATSCH, J. F., 1909. Zur Anatomie und Histologie des Verdauungstraktes der Sirenia. II. Die
Zunge von Manatus latirostris Harl. Morph. ]b., 40: 184-194.
HILL, W. W.C.O., 1945. Notes on the dissection of two dugongs. J. Mammal., 26: 153-175.
HusAR, S. L., 1978. Dugong dugon. Mammalian Species, 88: 1-7.
KOMATSU, S. and F. YAMASAKI, 1980. Formation of the pits with taste buds at the lingual root in the striped
dolphin, Stenella coeruleoaha. j. Morph., 164: 107-119.
MAYER, F.J.C., 1844. Uber die Zunge als Geschmacksorgan. Nova Acta Acad. Leop. Carol., 20: 721-748.
MURIE,]., 1870. On the form and stucture of the manatee (Manatus americanus). Tran. Zoo[. Soc. London,

8: 127-202.

* As mentioned above, this seems to be the structure corresponding to our dorsal swelling.
Sci. Rep. Whales Res. Inst.,
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138

YAMASAKI, KOMATSU AND KAMIYANAIR, R. V., R.S.L. MOHAN and K. S. RAo, 1975. The dugong, Dugong dugon. Cent. Marine Fish. Res. Inst.
Cochin, 26: 1-42.
OWEN, R., 1868. Organ of taste. In: On the anatomy rifvertebrates. Vol. III. Mammals., Longmans, Greenand Co., London, pp. 193-194.
RAPP, W. VON, 1857. Anatomische Untersuchungen tiber Manatus (Lamantin). Jahrh. Ver. vateral. Natkd.
Wurttenburg, Stuttgart, pp. 87-98.
SHIMIZU, Y., T. FUJITA, T. KAMIYA and S. IsoKAWA, 1960. Anatomy of a female Indian elephant with special reference to its visceral organs (in Japanese with English summary). Acta Anat. Nipponica, 35: 261301.
SONNTAG, C. F., 1922. The compartaive anatomy of the tongue of the mammalia. VII. Cetacea, Sirenia
and Ungulata. Proc. Zool. Soc., London, pp. 639-646.
WEBER, M., 1904. Sirenia. In: Die Saugetiere. Verlag von Gustav Fisher, Jena, pp. 727-741.
YAMASAKI, F., H. SATOMI and T. KAMIYA, 1976a. The tongue ofFranciscana (La Plata dolphin), Pontoporia
blainvillei. Okajimas Fol. anal. jap., 53: 77-92.
YAMASAKI, F., H. SATOMI and T. KAMIYA, 1976b. An observation on the papillary projections at the lingual
margin in the striped dolphin. Sci. Rep. Whales Res. Inst., 28: 137-140.
YAMASAKI, F., S. KOMATSU and T. KAMIYA, 1978a. Papillary projections at the lingual margin in the.striped
dolphin, Stenella coeruleoalba, with special reference to their development and regression. J. JY!orph.,
157: 33-48.
YAMASAKI, F., S. KOMATSU and T. KAMIYA, 1978b. Taste buds in the pits at the posterior dorsum of the
tongue of Stenella coeruleoalba. Sci. Rep. Whales Res. Inst., 30: 285-290.
YAMASAKI, F., S. KOMATSU and T. KAMIYA, 1980. An anatomical note on the tongue of dugongs, Dugong
dugon. Proc. Seminar Workshop Dugongs James Cook Univ. in 1979, (in press).

Sci. Rep. Whales Res. Inst.
No. 32, 1980

TONGUES OF THE SIRENIAEXPLANATIONS OF FIGURES
Fig. I. A dorsal view of the tongue of an African manatee (TS-2). The tongue israther slender as a whole, and its tip is rounded. The tip region is covered withmany hard, digitiform, cuticular spines. Dorsal multifossulate swellings, slightly
opened anteriorly, forming a pair may be observed near both posterior lateral
margins of the dorsum. Numerous small openings of mucous glands are visibleon the posterior part of the dorsum. X 1.
Fig. 2. Left side view of TS-2 tongue. The tongue becomes thick posteriorly but
thin at the lingual root. A lateral multifossulate swelling is observed in the anterodorsal region of the palatoglossal arch. Some twenty-five round fiat patches
are present, extending from the anterior fifth of the side wall to near the palatoglossal arch. Small mucous glandular openings are visible from the mid-part tothe arch. X 1.
Fig. 3. A higher magnified view of the left dorsal swelling of TS-2 in figure I.
Roughly twenty-five rather oval, large fossulae are obviously visible on the swelling. Numerous glandular openings, far smaller than the fossulae in diameter, areclearly seen from the posterior region of the swelling to the posterior part of the
tongue. x2.
Fig. 4. A left dorsal swelling of a West Indian manatee (TM-I). The swelling,having many large fossulae, is not as remarkable as that ofTS-2. X2.
Fig. 5. A higher magnified view of the lateral swelling of TS-2 tongue in figure 2,
showing more than ten oval fossulae. Numerous glandular openings, far smaller
than the fossulae in diameter, are observable. x2.
Fig. 6. A dorsal view of the tongue of a dugong (DD-3). The tongue is rather
slender as a whole, with the spine-covered tip region being truncated. Thin, soft
spines extend posteriorly, being especially shaggier on the lateral strips. Smallelevations are seen on the dorsum. A row of dorsal pits can be seen at both posterior margins (arrows). x I.
Fig. 7. Left side view of DD-3 tongue. The body of the tongue strongly bowsanteroposteriorly, with the root being situated at a lower level to the body. Three
lateral pits are observable on the posterior side wall (arrow). About fifteen roundflat patches are present on the mid-part of the side wall. X 1.
Fig. 8. Bunches of spines grow on the small elevations at the anterior dorsum of
the DD-3 tongue. x20.
Fig. 9. A higher magnified view of the dorsal pits on the left side of the dorsum of
DD-3 in figure 6. Small mucous glandular openings can be seen on the posterior
part of the pits. X 2.5.
Fig. 10. A higher magnified view of the lateral pits and patches of figure 7. The
pits and patches vary in size. Small mucous glandular openings are observableon the ventral side of the pits and patches. X 2.5.
Fig. 11. A cross section of both dorsal swellings with fossulae in an African manatee(TS-1). Mixed glands are present in the regions with fossulae, whereas in thearea between both swellings the submucosa is occupied by pure mucous glands.
x5.5.
Fig. 12. A cross section of two fossulae of a dorsal swelling of TS-1. Several fiaskshaped spaces in the epithelium of the side wall of the fossulae may show the remnants of taste buds, the cells of which have sloughed off. Glands are, for the mostpart, mucous in nature but partially mixed, especially in the upper part of thegland mass. Capacious ducts are seen at points in the glandular tissues. The
secondary papillae of the side wall of the fossula are poorly developed. X 15.
Fig. 13. A cross section of a fossula of a dorsal swelling of TS-2. Mucous glands

Sci. Rep. Whales Res. Inst.,
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139

YAMASAKI, KOMATSU AND KAMIYA

140

more developed than those of TS-1 are seen but serous glands intermingle partiallyat the bottom of the fossula. The thin epithelium of the inner wall of the fossula
has exfoliated due to its poor condition. X 15.
Fig. 14. A cross section of two fossulae of a dorsal swelling of the West Indian
manatee (TI-I). Well developed glands are mostly mucous in nature, but partially mixed in the upper part of the gland mass. X 15.
Figs 15 and 16. Cross sections of two fossulae (TS-1, Fig. 15) and a fossula (TS2, Fig. 16) of the lateral swelling. The nature of glands is almost the same as thatof the dorsal swelling, but the glands of the lateral swelling are poorly developed
as compared with those of the dorsal swelling. These glands are well developedin TS-2 as compared with those in TS-1. X 15.
Fig. 17. A cross section of a dorsal pit of a dugong (DD-3). Small projections canbe seen in the pit. The pit is surrounded by well developed serous glands (Sg)which are clearly distinguished from mucous glands (Mg). The epithelium of thepit is very thin. X 7.5.
Fig. 18. A cross section of a lateral pit of DD-3. A small projection having taste
buds in its thin epithelium can be seen in the pit surrounded by well developed
serous glands. X 25.
Fig. 19. A more highly magnified view of a part of the projection in figure 18.
Taste buds lie in the thin epithelium of the projection. This figure is taken fromthe area where taste buds are crowded together. X 300.
Fig. 20. A cross section of two patches of TS-2. The epithelium is rather thin andsecondary papillae are poorly developed in the patches as compared with those of
the remainder. Mucous glands and a glandular opening can be seen in the lower
patch. X 15.
Fig. 21. A cross section of a patch of DD-3. The epithelium is rather thin as compared with that of the remainder. Mucous glands can be seen in places. X 15.
Fig. 22. A more highly magnified view of a cross section of a patch of DD-3.
Abundant, rather thick nerve fibers are observable in the submucosa of the patch.

x50.

Sci. Rep. Whales Res. Inst.,
No. 32, 1980

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