AN OBSERVATION ON THE PAPILLARY PROJECTIONS ATTHE LINGUAL MARGIN IN THE STRIPED DOLPHINFUSAO YAMASAKI
Department of Biology, Sapporo Medical College, Sapporo

HAJIME SATOMI
Department of Anatomy, Sapporo Medical College, Sapporo

AND
TOSHIRO KAMIYA
Department of Anatomy, Faculty of Nfedicine, University of Tokyo, Tokyo

ABSTRACT

Papillary projections were observed along the anterolateral marginsof the tongue in fetal and young stages of the striped dolphin, Stenella
coeruleoalba. The projections appear in the fetal stage and attain maximum development in the early postnatal period. They disappear almost
completely by weaning, although small vestigial eminences remain at thecorresponding region in the adult. The projections may have a close
relation to suck milk.

There are few descriptions of the anatomy of the tongue in Cetacea, and many
uncertainties remain concerning lingual structure and function in many speciesof this order of mammals. One of the most remarkable features of the tongue
in Cetacea is the completely absence of lingual papillae.
We have found papilla-like projections at the anterolateral margin of thetongue in fetal and young individuals of some species of dolphins. Growthand involution of these projections were demonstrated in the striped dolphin,
Stenella coeruleoalba. The fact that the projections appear temporarily, anddo not persist throughout life, has not been reported previously.
As shown in Fig. 1, small projections, approximately 0.5 mm in length andabout twenty in number on each side, are present at the lateral margins of theanterior one-third of the body of the tongue in a 27 cm fetus. The projections
are distinct (1 to 2 mm long) occupying the entire anterior margin of the tongue
in an 80 cm fetus. In a 98 cm fetus, they have grown longer (2 to 5 mm) andwider than those in the 80 cm fetus (Fig. 2) and some of them are subdivided
at their tips (arrows in Fig. 2). In a young Stenella (body length 150 cm),
projections have become somewhat thinner and broken, and some of them havedisappeared in the posterior part (Fig. 3). In an adult animal, several distinct
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YAMASAKI, SA TOMI AND KA:\1IY A

eminences are present near the apex of the tongue (Fig. 4). In another larger
adult one, the eminences have reduced in size and the lateral margins areslightly uneven in appearance. The entire dorsum of each tongue we observed
was quite smooth and no lingual papillae of any type were present.
Since the body length of Stenella coeriileoalba is about 100 cm at the timeof birth (Kasuya, 1972), the appearance of the tongue in the newborn animal
is probably similar to that in the 98 cm fetus we observed. Thus, it is certainthat the papillary projections in the Stenella appear during intrauterine lifeand gradually develop towards parturition. The projections may be mostnumerous and well developed in the early postnatal period and they may begin
to degenerate and disappear at about the 150 cm stage, which roughly corresponds to weaning in Stenella coeritleoalba (Kasuya, 1972). How the numberof the projections increase and how the projections disappear are interestingpoints. It can be assumed that the former increase due to subdivision of theprojections that arc present in the 98 cm fetus as shown with arrows in Fig. 2,and the latter vanish through repeated narrowings in several parts of eachprojection (arrows in Fig. 3) and finally shed off from the tongue proper.
In the adult Franciscana dolphin, Pontoporia blainvillei, no papillae werepresent on the dorsum of the tongue but small eminences were observed at its
lateral margins. Distinct papillary projections (2 to 3 mm long) were foundat the anterior free margin of the tongue in a young, 98.5 cm, Pontoporia(Yamasaki, et al., 1976), and the same region was dotted with warts and fringes
in a young animal (Burmeister, 1869). The small eminences at the anterolateral
margins of the tongue of the adult Stenella and also of the adult Pontoporia
appear to be the remnants of the papillary projections seen in the younganimals. We also observed well developed projections (2 to 4 mm long) at theanterior margin of the tongue in a newborn finless porpoise, Neophocaena
phocaenoides (71.5 cm). And foliate projections (3 to 6 mm), which decrease in
their number with age, were observed in young bottlenose dolphin, Tursiopus
truncatus, and Risso's dolphins, Grampus griseus (Nakajima, et aL, 1963). Thus,
the papillary projections will be found in the fetuses and the young of someother dolphins or toothed whales. Although Anderson (1879) and Sonntag (1922)
described filiform and fungiform papillae on the tongue of Ganges dolphin,
Platanista gangetica, the dorsum of the tongues of the adults was completely
smooth and no type of lingual papillae could be observed (Arvy and Pilleri,1970, Yamasaki, et al., 1976). As they only observed the tongue in the young
stage without observation in the adult, projections were propably described as
the lingual papillae mentioned above.
The projection is composed of a core of the lamina propria mucosa anda thick stratified squamous epithelium without taste buds. Both are continuouswith those of the tongue proper. This structure, as a whole, is similar to thatof filiform or fungiform papillae. However, the projections differ markedly
from the lingual papillae of the general mammalian tongue in that they aretemporary, localized at the anterolateral margin in a radial manner and large
Sci. Rep. Whales Res. Inst.,
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LINGUAL PAPILLARY PROJECTION OF DOLPHIN

139m size.

Sonntag (1922) stated that the apex of the tongue in toothed whales
may or may not have processes and warty growths, however, we suppose that
he observed the tongues in variable stages of involution of the papillary
projections. Since the projections only appear in a specific period during
life, more care is neccessary as to the estimation of the age when observing
the appearance of the cetacean tongue.
The function of the lingual papillary projections described above is notknown. Because they are well developed during the suckling period they may
have an important mechanical functions during suckling in these aquatic
mammals.
As there as yet seem to be several unclear and interesting problems
concerning the papillary projections in dolphins, further observations will bedone on the relationship between the existence of the projections and thesuckling period as well as on food habits and on the process of their development
and degeneration, macro- and microscopically. In addition, comparative
functional anatomical studies with other cetaceans will be neccessary to clarify
this problem.
ACKNOWLEDGMENTS

Greatest thanks are due to Dr. M.M. Bryden, School of Anatomy, Universityof Queensland, Australia, who gave us valuable suggestions and kindly checked
the draft. Dr. T. Mitsui, Department of Anatomy, Keio University, Dr. T.
Ogawa, Department of Medical History, Juntendo University, Dr. K. Takahashi, Department of Anatomy, Sappro Medical College, Dr. H. Ohmura,Whales Research Institute, Dr. T. Kasuya, Ocean Research Institute, Universityof Tokyo, and Dr. R. L. Brownell Jr., Department of Vertebrate Zoology,
National Museum of Natural History, Washington, D.C. are also acknowledged
for their advice for our study.
REFERENCES
A'iDERSO'i, J., 1879. Anatomical and zoological researches: comprising on account of the zoological results of the two expeditions to Western Yunnan 1868 and 1875; and a monographof the two cetacean genera, Platanista and Orcella. Vol. 1, pp. 433-435, Quaritch, London.
ARVY, L. and G. PILLER!, 1970. The tongue of Platanista gangetica and remarks on the cetacean
tongue. In: Investigation on cetacea., Vol. II, ed. by G. Pilleri, 75-77, Berne.
BURM El STER, H., 1869. In: Descripci6n de cuatro especies de delfinides de la costa Argentina
en el Oceano Atlantico. Anal. Mus. Publico Buenos Aires., 1 : 348-445.
KASUYA, T., 1972. Growth and reproduction of Stenella caeruleoalba based on the age determination by means of dentinal growth. Sci. Rep. Whales Res. Inst., 24: 57-79.
NAKAJIMA, M., K. TAKAHASHI, M. 0GURA, and K. SAWAMURA, 1963. On the growth of infantsof the small size toothed whales. J. Jap. Assoc. Zool. Gard. Aqua. Tokyo, 5: 16-22. (in Japanesewith English summery).
SONNTAG, C. F., 1922. The comparative anatomy of the tongue of the Mammalia. VII, Cetacea,Sirenia and Ungulata. Proc. Zool. Soc., 639-646.
YAMASAKI, F., H. SATOMI, and T. KAMIYA, 1976. The tongue of Franciscana (La Plata) dolphin,
Pontoporia blainvillei. Okajimas Fol. anat. jap., 53: 77-92.

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YAMASAKI, SA TOMI AND KAMIYAEXPLANATION OF PLATE I
Four stages of the growth and degeneration of the lingual papillary projections of
the striped dolphin, Stenella coeruleoalba.
Fig. I. Small projections have already appeared at the lateral margin of the anterior
part of the tongue in a 27 cm fetus.
Fig 2. Projections in a 98cm fetus are distinct and occupy the entire anterior marginof the tongue in a radial manner. Some of the projections are subdivided at theirtips (arrows). The dorsum of the tongue is concave along the long axis.
Fig. 3. In young Stene/la (150 cm), projections have become thinner and some at theposterior part have been broken and have disappeared. Note the narrowing seen
in some projections (arrows). The transverse and longitudinal incisions were madeto improve fixation.
Fig. 4. Vestigial small eminences of the projections can be seen at the margin near
the apex in an adult.

Sci. Rep. Whales Res. Inst.,

No. 28, 1976.

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