Sinus-hairs of the Sei-vVhale (Balaenoptera borealis)byJunnosuke Nakai and Toshitomo Shida(Director: Dr. Teizo Ogawa)
Sinus-hairs of a whale possess sensitive tactility like the whiskers of acat. The root of this hair is surrounded by blood sinus in the connectivetissue layer of the hair follicle. It is a venous sinus with numerous nerves
coming into the sinus and twining themselves around the root of the hair.
The whale-bone whales have these characteristic sinus-hairs on their
upper and lower beaks, but in dolphins they occur only in their foetusstage and degenerate after birth.
The lack of sinus-hairs in dolphins is believed, generally, to be due tothe food of them, being so large as to be easily visible that tactile hairs
become unnecessary, but, the food of the baleen whales is tiny Mysidae
and is so difficult to see that they search for the food with these hairs.
In the summer of 1946 and 1947, at Ayukawa, Miyagi Prefecture, we
had a chance to. study sinus-hairs of Sei-Whales, Balaenoptera borealis,which were caught off the coast of Kinkazan and studies were made bothat the whaling station and in the laboratory later. The distribution andnumber of sinus-hairs macroscopically and some facts on histological preparations have been studied.
D. G. Lillie (1910) merely studied thE distribution and number, while
A. Japha (1910) devoted himself to the microscopic study of histologicalpreparations.
We observed, at the whaling station, some white, weak hairs of 1 to
2 cm in length occurring on the giant body, generally symmetric~lly inspecific arrangement. The observation at the whaling station was not easy;because of the giant body and of the speedy disposition of it. It wasalmost impossible to count and examine the hairs of both upper and lower
beaks of an individual.
The arrangement and number of these hairs are shown in Table 1 and. in Figs. 1 and 2. There are four rows of them on the dorsal surface of
the upper beak, from the anterior extremity to the blow-hole, almost 30
hairs at each distance of 20-30 cm. At the anterior end of the lower jaw,
there are two rows which occur closely together along the median line at

J, Nakai, T. Shidaupper

beaklower

beakI

Individual

right
left
rightleft
1·
on the la- rat the an- .onthe la- 'at the an--=.
outer row mner row outer row mner row teral side terior end teral sidel terior end•-N-0-.-1--1--1-0-

5- - - - - _____ ,___9__ 1----1-,-,

No. 2

8I

No. 3

4

11

114/

14

--- --1---~

II

1614

Table 1. Number of sinus-hairs of Sei-Whale_,,.

~~-__j_._......_,...

.....

~ ===-::::::--~--------~~-----

Fig. ?· Sinus-hairs at the anterior
end of lower beak.

Fig. I. Arrangement of sinus-hairson the head of Sei-Whale.

a distance 1 to 2 cm and contain almost 30 hairs. On each lateral side oflower jaw, there is a row of from 5 to 10 hairs. There are a total of nearly
80 hairs in all which does not greatly differ from reports of the former
investigators.
We especially made a study of the hairs at the anterior end of lower
beak. We made observations at first by naked eye or with a magnifyingglass inflicting small cuts in the sinus and its neighbouring parts. By thismeans, we were able to unearth some new facts which seemed to haveescaped notice of earlier workers.
When a large blood sinus, surrounding the hair root, was carefullySinus.hairs of the Sei·Whaleobserved, the skin above it was indented in a funnel shape and becamevery thin at the point where the hair came· out of the sinus, and the sinus
extended itself to just beneath the epidermis.
At the bottom of the funnef shaped dent, the thickness of epidermis
is only 0.3 mm, but it becomes thicker outward, being 1.3 mm thick at theperiphery of the funnel. The corium layer between the epidermis and theblood sinus is only 0.1 mm in thickness.
The sinus-hair is supported in the sinus by many threads from surrounding walls so that the hairwill move freely in all directions whenpressure is applied from outside. It is significant that this part of theepidermis where the hair comes out is very thin in order to make thismotion easily.
Observations of the cross section of the hair follicle show that thishair is situated not equally distant from inner walls ·of the sinus, but iseccentric. Furthermore, the inner walls of the sinus are different inshape, such that the side to which the hair shaft is inclined is almost
vertical, but the wall on the opposite side forms a curve, of which thecentral part swells out remarkably (Fig. 3).
The longitudinal diameter of the sinus is almost 12 mm, maximum
transverse diameter almost 2 mm. The wall of the sinus is made of denseconm:ctive tissue fibers, looking somewhat like the tendon, and is about
1 mm in thickness at the central swollen part. These fibers give off
branches radially into surrounding parts of the corium so that the swollen
part seems to be strongly pulled outwards.
In the skin of the whale, there is only a thin compact layer of connective tissue between the epidermis and the adipose tissue of the subcutaneous layer. Coarse fiber bundles run in complicated directions through theadipose tissues, but, as no remarkable connective tissue fibers are seen in
the neighbourhood of the hair follicle except the above-mentioned radial
fihers, the hair follicle lies nearly surrounded by soft adipose tissues.
We thought that there might be a rule between the eccentric locationof the hair root in the sinus, shape of the sinus walls, and the inclinationof the hair shaft. By a closer observation, it was found that the hair shaft wasalways inclined towards the side to which the hair root was located nearer.
Further observations revealed that the epidermis forming the funnel at theexit of the hair has a gentler slope on the side the hair shaft is inclined

J. Nakai, T. Shida

44and the other side constitutes an almost perpendicular wall (Fig. 3).

sheath of the hair root
threads of connective tissue
venous sinus

covering

connective fibers coveringa nerve bundle
Fig, 3 Root of a sinus-hair and its surroundings
medial side

median line of theanterior end of thelower beakFig. 4, To show the inclination of sinus-hairs

Sinus-hairs of the Sei-Whale

45

Therefore, the direction of inclination of the hair shaft seemed to havesome intimate correlation to the structure of the sinus. Bwt since we could
not make any further generalization on a small piece cut out from the lower
jaw, we proceeded then to the examination of the entire tipe of the lower
jaw, where each direction in relation to the whole body is easily determinable. It was made clear that the hair was always inclined to the lateral
direction (Fig. 4). Therefore, the swollen part of the sinus wall is on themedial side, namely, on the side directed to the median line.
The shaft of the sinus-hair shows no pigmentation and is 0.1-0.15 mm
in diameter, being the thinnest at the exit. Its surface is relatively smooth
only at the part, where it just comes out of epidermis and its tip has many
protrudings and looks like a slender tree trunk with many knots (Fig. 5).
While treating the hair under a microscope, it was found that dust adheres
easily to the hair shaft. The hair has no marrow; bulbus and papilla ofthe hair are divided in complex form.
Next, the nerves come into consideration. We observed both in macro
germinal layerof epidermis

4 mm

2. mm

vein0

Fig. 5. shaft of a sinus-hairFig. 6. Lamellar corpuscles in thesuperficial part of a hair-follicle

46J. Nakai, T. Shidaand microscopical sections, a relatively thick bundle of nerve fibers ascending almost vertically and it gave off one branch entering the hair follicle
from just beneath it and the other branch ascending outside of the follicle.
According to Japha, as several hundreds of myelinated nerve fibers
are counted in one sinus-hair, there must be almost 10.000 fibers at theanterior end of the lower jaw, and he quoted in relation to this an interesting story, told by Malm (1866) that when one touched the lips of a Blue
whale washed ashore alive near Goteborg in Sweden this giant whale started
violently.
We ascertained by microscopic observations that the ascending nerve
bundles end in special terminal apparatus, in the outside of the sinus.
This apparatus resembles the Pacinian corpuscle, but since the number oflamellae is so few that, it comes nearest to the Herbsti's corpuscle.
They are nearly oval, 60-300 µ in length, 20-150 µ in transverse
diameter, and are made of concentric lamellae of connective tissues. The
axis of the corpuscle is occupied by a well developed eosinophile core,containing the termination of a nerve fiber (Fig. 6).
The corpuscles are grouped in the following wise: one group about 1
mm immediately beneath the epidermis, on the lateral side of the hair ;another group about 1.5 mm in length on the opposite side (median); thethird group on the lateral side (same side with the first group) somewhat
beneath the second, and also at the height of the hair papilla, where more
corpuscles are obviously seen on the median side than on the lateral side.
Further researches are needed as to the distribution of the terminal apparatus and differences in its size according to location. We can, however,assume that this distribution of the corpuscles has a close connection withthe functional direction of the hair, when the hair encounters pressure andresistance. Japha also observed that there were especially numerous small
terminal corpuscles (about 20 x 60 µ) in the papillae of corium immediately
beneath the epidermis around the hair.
We are endeavouring to throw more light by the method of axis
cylinder staining on the distribution of nerve fibers to the corpuscles andto study the characteristic feature of nerve fibers at the point, where thesinus continues into a vein.
The inner surface of the venous sinus, as well as nerves, blood vessels
and threads of connective tissues which are all present inside the sinus are•Sinus-hairs of the Sei-Whale47

covered by endothelial cells.
According to macroscopic studies, a relatively thick artery, being thesize of a thin needle, runs up from the under and lateral direction andenters the sinus through the lower lateral part of the hair follicle, aboutat the height of a hair papilla. The artery entering the sinus is divided
into two, runs upward and. becomes more brouched and thinner.
A large amount of blood sent into the sinus from the lower part, runs
up and seems to flow out into a vein near the epidermis. The exit issituated on the opposite side to the artery, namely on the median side.
The terminal corpuscles are crowded in this side near the exit.
It is especially worthy of notice, in the above-mentioned results, thata rule of direction exists between the sinus-hair and things accompanying
it, as a whole. For this reason, the sinus-hair seems to have a greater
significance in the life of a baleen whale than it has been assumed as atool for finding food. We suppose that by use of sinus-hairs the whales
might feel the currents of water upon their beads.
Ki.ikenthal was of the opinion that the scanty remaining hairs of whales
are merely a reduced organ, as they have no sebaceous glands. But it is
the common property of the skin of whales that it lacks not only thesebaceous glands, but also the sweat glands. We are of the opinion, thesinus-hairs of whales seem to be a very important sensory organ for thelife of them.
Literature
Japha, A. : Die Haare dtr Waltiere. 1910. Zool. Jahrb. Bd. 31-. Abt. f. An1lt. (Sonderabdruck).
K:iikenthal, W.: Untersuchungen an Walen. 1909. Jena. Z. f. Naturwiss. Bd. 45. S. 545-588.
Lillie, D. G.: Observations on the anatomy and general biology of some members of the larger
cetacea. 1910. Proc. Zool. Soc. London. p. 779-792.
Tretjakoff, D.: Die Nervenendigungen an den Sinushaaren des Rindes. 1911. z. f. wiss. Zool.
Bd. 97. S. 314-416.