On. the Brain of the Sperm Whale(Physeter Catodon L.)

BY
TOKUZO KOJIMA
Brain Institute, University of Tokyo.
(Prof. Dr. Teizo Ogawa)

During the Antarctic expedition on board the Japanese whaling
factory ship "Nissin Maru No. l" in the season of 1949-50, I haveundertaken to investigate the brain of the Sperm whale upon thefollowing points.
( I ) Brain weight(II) Macroscopical observation on the cerebral hemispheres especially on the fissures and the gyri(III) Cytoarchitecture of the cerebral cortex
The brain weight (I) was surveyed on the deck, while the otherstudies (II and III) were later performed at the Brain Institute, University of Tokyo, upon materials fixed in formalin.
In the Antarctic Ocean we captured none of female and infantile
Sperm whales but only males of over 40 feet length. During the expedition the Nissin Maru could get 172 Sperm whales, in which only
7 (4.1%) were sexually immatured.
(I )Brain weight

The brain was taken out from the huge cranium, using such tools
as chisel, gimlet or hatchet, after the bone was cut by a bone-saw
into a block properly shaped for extraction of the brain, or after
sagittal sectioning of the cranium into halves, two separated parts ofthe brain were gathered.
The brain weight was measured with the steelyard (the measurelimit: 100 g), without stripping off the pia mater, because the brain
substance is too soft to isolate it safely from the pia mater.
As the spinal cord was usually transected at the occipital condyles,
its upper part, more rostral than the place of the IV cervical nerveroots, was attached to the brain.
The brain weights of 16 Sperm whales, of which the average bodylength is 49.8 feet, are shown in Table 1. This average body lengthis nearly equal to that (49.9 feet) of the total (172) Sperm whales
captured. The brain of No. 3 (*l) weighed very light (6.4 kg); as the

T. KOJIMA

50

Table 1. Brain weights, measured fresh, o{ 16 Sperm whales
Date ofMeasurement

5/XII, 1949
II

II

II

II

II

II

7/XII,II"II

9/XII,
11/XII,

II
II

II

II

12/XII,

II

II

II

14/XII,
15/XII,

II

II

JJ

II

JI

II

JI

II

.

Brain /Body
Brain weight Body length weight
No. of thelength(feet)(kg)
Sperm whale(kg)(feet)

1
2
3
4
5
6
7
98
99
108
110
122
123
125
153
154

8.0
7.0
6.4 *I
7.3
7.7
7.0
8.7
9.2 *2
8.6
9.0
8.0
7.0
8.0
7.0
8.0
8.2

50
49
54
49
50
52
54

49
46
51
49
49
54
51
51
49

0.160
0.142
0.118
0.148
0.154
0.134
0.161
0.187
0.186
0.176
0.163
0.142
0.148
0.137
0.156
0.167

cranium of this individual was fragile, the whale was estimated as avery old one, while the most heavy brain of No. 98 (*2) belonged to
an individual, which seemed to be in full maturity, as the brain substance and the cranium were felt very hard.
Naturally I had an interest in knowing the ratio of the brain
weight to the body weight, but it was impossible to determine thelatter ; moreover, even during the short season from beginning tillend of December the Sperm whales increased considerably in the bodyweight, as they eat much food in the meantime ; therefore the bodyweight varied to a high degree.
On the other hand, the ratio of the brain weight (kg) to the bodylength (feet) was easy to determine. Its individual difference wasgreat, between 0.118 as minimum and 0.187 as maximum, the average
being 0.154. We know that the brain weight bears no direct ratio tothe body length. Considering the fact that the Sperm whales caught
in the Antarctic are all males and almost all of them are fully matured,
the difference in question seems to have some relation to the degreeof senility.
It should be noted here that scarcely any reference has ever been
made to the . brain weights of the Sperm whale, ~hough those of some
Mystacoceti and of other Odont0ceti have been sometimes studied. But

On the Brain of the Sperm Whale

51

even in these cases they were surveyed under different conditions as
to fixation, its duration, the meninges contained or not, and the age,often including embryos.
GULDBERG reported the brain weight of a Blue whale of 60 feetlength, measured fresh inclusive the pia mater, arachnoides, and blood,as 6700 g, and the dura mater and rete mirabile of it as 3050 g. He
said also that the brain fixed a few weeks in alcohol of a Blue of 64
feet length weighed 4673 g, and that the brain of a Fin whale together
with the dura mater and rete miriable was 13680 g, after 8 weeks'
fixation in alcohol. According to him, the brain weight had beenmeasured by KNOCH and HUNTER in Balaenoptera rostrata, by SCORESBY
and RUDOLPHI in Balaena mysticetus, and by EscHRICHT in Megaptera
hoops. After all, we know in the literature GULDBERG's only one case,when the fresh brain was measured in a whale of over 50 feet length;
other reports concerned always the weights after fixation, or the brainof smaller whales, mostly of dolphins and porpoises. The brain weights
measured by me in Physeter seem to be,.. though they are quite difficult to compare, heavier than those of Mystacoceti of over 50 feetlength.
.
AccorCl.ing to GULDBERG, the brain weight· loses about 1/3 after
fixation in alcohol. I myself fixed pieces of the cerebral cortex of theSperm whale in 10% and 20% formalin and followed how they change
in weight by fixation ; the results are shown in Table 2. I reached
Table 2.

Changes of the weight of brain substance during
fixation. in formalin solution (200 cc)
in 10% formalinin 20% formalin

Weight before fixation

21.5g

15.0g

9.8g

39.4g

After 24 hours' fixation

29.2g

21.0g

13.2g

50.0g

After 29 hours' fixation.31.2g21.Qg·l3.2g

51.2g

After 98 hours' fixation

31.0g

22.0g

13.2g

51.0g

Ratio of increase

44%

46%

34%

29%

the opinion that the ratio of. increase is smaller as the size of the fixed material is larger and the increase stops nearly after 29 hours'
fixation. In cases of such large materials as the cetacean brain thepermeation of the fixing fluid occurS quite uncertainly and ineompletely, for example we found that after 7 months' fixation in 10% formalin
the brain of the Sperm whals showed very few fo.filtration of the fluid

T. KOJIMA

52

even in the relatively small outlined brain stem ; therefore I think theweight after fixation is quite unreliable.
Now that the brain weights reported in the present paper include
pia mater, blood vessels and the cranial nerves of various lengths areattached, they can never be said to represent the genuine weight ofthe brain substance itself. There can be errors of about 500 g.
(II)
1)

Macroscopical observation on the brain especially on
the gyri and the fissures of the cerebral hemisphere

Weight, volume and dimensions

The brain of a Sperm whale of 50 feet length was examined indetails. It weighed 8.2 kg inclusive of the pia mater, which was attached
to medial and basal parts of the hemisphere and to the brain stem.
- - - - ---- -l!().Bcm- - - - - -- -F1o:.lFig. 1. Size of the brain of a Physeter.

The volume of the whole brain measured by the displacement ofwater is 8050cc. The specific gravity as the whole is therefore 1.01.
The brain was deformed to a certain degree during fixation in formalin.
Especially the basal surface was pushed by the bottom of the vaseand the vertical axis was shortened, while the transversal and sagittal
axis became larger. Because of the deformation the following data
must be a little different from the size of the brain in the living state(fig. 1).
Sagittal axis : 25.5 cm. This is the longest distance between theOn the Brain of the Sperm Whale

53

frontal and occipital extremities. The difference between both hemispheres is very slight (left 25.4 cm, right 25.5 cm).
Transversal axis: 30.8 cm, with some asymmetry. The right hemisphere 15.8 cm ; the left one 14 cm. It was already pointed out by
GULDBERG and RAWITZ in Mystacoceti that the right hemisphere isbroader than the left.
Vertical axis: 17.5cm. This must be smaller than in the living
animal, as mentioned above.
The ratio between the sagittal and the transversal axis is 0.822 :1, the latter surpassing the former. In the Mystacoceti (Balaenoptera
sibbaldi, B. rostrata and B. musculus etc.) the ratio comes very near
to 1: 1. Therefore, the Sperm whale is extraordinarily brachycephalic.
The cerebellum is 10.8 cm sagittally and 16.4 cm transversally.
2) Brain stem and cranial nerves (fig. 2, 4 and 8)
In addition to the above mentioned specimen, I could use the brainof another Sperm whale for the morphological observation of the brain
stem and cranial nerves. Viewed from antero-basal (fig. 4 and 8) thetelescoping of the brain isquite remarkable ; that is,
the axis of corplis callosum
is directed at a right angle
supraoccipitaJ \to the axis from midbrain
to pons and the latter axis
forms again nearly a rightangle with the axis frompons to the upper part ofoccipital
the spinal cord. The spinal
superior
cord shows in its upper part
~anteriora very unusual spatulate
basisphenoid
bending. It runs at first
Fig. 2. Peculiar bending of the axis of brain
along the occipital edge ofstem (dotted line) projected to the lateral
the cerebral hemisphere,
surface.
reaching far above the surface of the hemisphere (fig. 2).
Cranial nerves :The olfactory bulb and tract could not be seen. But in the otherbrain of the same species we noticed a mere trace of the nerve, which
begins from the olfactory area and runs together with a very small
vein along the olfactory fissure.

I;

54

T. KOJIMA

The oculomotor nerve appears as a few small roots, ventro-medial
to the cerebral peduncle and is immediately gathered into one bundle
running ventrolateralwards.
On the basal surface of the brain :The olfactory area ( =substantia perforata anterior), relatively
large and swollen, has a shallow transversal furrow, and lies between
the under surface of the frontal lobe and the optic nerve. Its frontal
edge, differently than in Mystacoceti, is not divided into ecto- andentorhinal fissures and borders mediad on the frontal lobe by a very
shallow sulcus.
The cerebral peduncle is composed by two masses of fibers, theone running from dorso-lateral to ventro-medial, the other from dorsal
to ventral, a furrow showing the border between the two. The sizeof them are different between both sides; on the right the ratio is 1
to 3, on the left on the contrary the former protrudes like a boal
occupying about 2/3 of the whole peduncle. Besides on .• the left side
the · tractus peduncularis transversus of a transversal Y-form is seen,
but no such a tract exists on the. rig lit side.
On the ventral surface of medulla oblongata we see . a pair ofolivary eminences, along the outside of which one or two small groupsof longitudinal fibers (pyramidal tract) run uphead and seem to crossat the caudal end of medulla oblongata.
Up to the present the brain stem and cranial nerves of the Spermwhale have not been reported by any authors, though many works havebeen published on those of Mystacoceti and other OdQntoceti (HUNTER,
v. BAER, BRUNS, RAPP, MAJOR,. HERBERT, BEAUREGARD, HASWELL,.
WILLIAM, GULDBERG, RAWITZ, MILLER, LANGWOR'l'HY and ADDISON etc.).
Among them the works of GULDBERG and RAWJTZ on Balaenoptera
rostrata and that of LANGWORTHY on Tursiops truncatus are aspeciallyinteresting for comparison with the Sperm whale.
All of the Mystacoceti are said to have small olfactory bulb andtract, while the Odontoceti can be grouped into two; one group (embryoof Beluga, Hyperodon and Phocaena communis) having mere traces ofthem, and the other (Globicephalus melas, Delphinus delphis) showing
no residue of them. The Sperm whale belongs from my observations
to either of them, but more possibly to the latter group.
In Mystacoceti the oculomotor nerve comes out from the interped'uncular fossa, while in the Sperm whale it is a little apart fromthis fossa.
The two division of the cerebral peduncle above mentioned andOn the Brain of the Sperm Whale55

the existence of tractus peduncularis transversus have never been heardof the cetacean brains.
3) Gyri and fissures (fig. 3-10)
The configuration of the cerebral hemispheres of the Sperm whalelooks at first very much complicated, but after a closer inspection, we
recognize in the gyri and fissures a certain regularity which bears somedefinite resemblances to that in carnivores or ungulates.
Since GULDBERG published his classical work on the brain of thewhalebone whales (1885), almost all of the workers have adopted his
nomenclatures. On the dorsal surface of the hemisphere pretty paralleland more lateral to the inter hemispherical fissure (Fit) the lateralfissure (F 1) runs and on the inner and outer sides of this we see F.
endolateralis (F enl) and the F. ectolateralis (F ectl). About at middleof the lateral surface the F. sylvia is surrounded semicircularly by thethe F. ecto- and F. suprasy1via and the anterior surface has F. olfactoria, F. coronalis and F. praesylvia.
My own observations will be described in the ord!Olr of anterior,posterior, inferior, dorsal and medial surfaces of the hemisphere andsuch terms as "frontal", "occipital", "temporal", will be limited only
to the places quite near to each pole, because boundaries between thelobes can scarcely be determined in this whale.
A)

Fissuresa) Dorsal surface (fig. 3)
Nearly all of the fissures run here in sagittal direction without any
large transversal fissures.
i) F. praesylvia (F pr)
Though it is not quite sure whether this fissure corresponds tothat of carnivores and ungulates, I adopted this name considering its
situation in relation to the whole hemisphere.
This fissure is asymmetrical, for on the right its anterior end lies
lateral to the olfactory fissure, while on the left it is medial to thisand moreover, on the right its posterior end does not reach themedial surface, while on the left it reaches almost the F. splenialis.
ii) F. cruciata (F er)
In carnivores and ungulates this fissure courses quite transversely.
But in the whales nobody has remarked about it, except LANGWORTHY,
whose reference is but very insufficient. In the Sperm whale the F.
cruciata runs almost parallel to the posterior part of the F. praesylvia
and enters the medial surface. Its frontal part is not directedtransversally, but compared with other fissures, it is the most oblique

58

T. KOJIMAThis is a large nearly straight fissure between the pallial margin(Mantelkante) and the F. lateralis. On the right side it is interrupted
at one place and runs around the occipital lobe to reach the basal
surface after a long course, while on the left side it goes without
interruption to the neighbourhood of the occipital pole, assuming there
a complicated figure.
According to GULDBERG, this fissure is always present in Phocaena
communis, either combined with F. splenialis or bent into the medialsurface, but no such combination or bending was seen in the Spermwhale.
iv) F. lateralis (F 1)This very large and uncrooked fissure is located about at middle
between the ecto- and endolateral fissures. It runs quite symmetrically for a long distance along the lateral occipital part up to thelateral temporal portion. Though GULDBERG and RA WITZ pointed out
in B. musculus and B. rostrata that its frontal end often continues toF. coronalis and F. praesylvia, as this continuance occurs in carnivores,in the Sperm whale there are no direct connections between them.
v) F. coronalis. (F. co)
We can locate this fissure only with much difficulty. It is very
asymmetrical. On the left two crooked fissures run to the frontal
surface after being interrupted by F. lateralis and F. ectolateralis,while on the right a fissure which is continuous with F. cruciata andectolateralis reaches the anterior surface after being cut on the way
as on the other side. TURNER mentioned some variations of the F.
lateralis: it is continuous either with F. cruciata (Dictyles, a kind of
Ungulata) or with F. lateralis (cats etc.); in some other animals it
continues to neither of them. There are also individual differences.
In addition there are between the F. endolateralis and the interhemispherical fissure short fissures which run symmetrically (fig. 3, :If1). Other small quite asymmetrical fissures do not seem to be of muchsignificance.
b) Lateral surface (fig. 6 and 7)· Around the F. sylvia three semicircular fissures are arranged concentrically in the order from outside F. ectosylvia, F. suprasylvia andF. ectolateralis. Their forms are rather near to a circle than to a key,as this is the case in carnivores and ungulates.
vi) F. ectolateralis (F. ectl)
This is a quite symmetrical, large, very clearly defined sulcus,
running from antero-medial of the frontal lobe to postero-basal of theOn the Brain of the Sperm Whale59

temporal lobe, nearly parallel to F. lateralis.
vii) F. suprasylvia (F ss)
FI
F SS
On the left, the frontal F it
end of this fissure continues
directly to about the middle ofF. sylvia, while on the rightit starts from a lateral partof the frontal lo be and runs
parallel to F. sylvia, fromwhich it is completely apart(fig. 6 and 7).
viii) F. ectosylvia (F ects)
This also is different between both halves ; on the left
it is directly connected with
F. sylvia. Quite a long andF ectldistinct fissure, a little asymmetrical, runs along with F.
suprasylvia and F. ectosylvia
Fig. 7. The left cerebral hemisphere ofparallel to them. On the
Physeter: Lateral viewleft a short sulcus connects F.

VII

VIII

F enl

Fig. 8.

Basal view of the posterior part of the Physeter~brain

On the Brain of the Sperm Whale61

suprasylvia with F. ectosyivia in the temporal lobe (fig. 7, :!*2), while on
the right in the lateral part of the frontal lobe a short sulcus runs
between these two fissures (fig. 6, :!*3) and besides a long distinct
sulcus courses from the frontal lobe to the temporal lobe (fig. 6, #4).
iv) F. sylvia (F S).
This is nearly symmetrical on both sides.
c) Posterior surface (fig. 5)
No symmetry is seen here. Especially the right shows very irregular sulci of very complicated form. On the left we see parallel tothe pallial margin the endolateral, the lateral, and the ectolateralfissures run side by side, while on the right the endolateral, fissure is notfound, but the lateral and the ectolateral fissures are present in thelateral border. On both sides sulci of the region between the pallial
margin and the lateral fissure show very complicated curving andbending, except the left F. endolateralis, which courses very distinctly
as mentioned above.
d) Medial surface (fig. 9 and 10)x) F. suprasplenialis (F ssp)
This long fissure shows no great difference between both sides.
It starts from F. cruciata and runs to about middle of the medial
temporal surface in a large semicircular form. It gives off many small
sulci at right angles. As discussed before, this corresponds in myopinion to F. suprasplenialis observed by GULDBERG in the Fin whaleand differs from "scissure endolaterale" mentioned by RICHARD in
Globicephalus melas. TuRNER reported this fissure in Balaenoptera
rostrata. But nobody seems to have found its continuance to F. cruciata. In carnivores and ungulates it is connected with F. splenialis
or intercepted from this by a gyrus ; so there is a possibility that thefissure in question corresponds to F. splenialis, but as a more probable
F. splenialis is observed in a more basal region, I identified it to F.
suprasplenialis.
xi) F. splenialis (F sp)
On both sides it begins from near the frontal pole and runs on
the medial surface as if encircling the corpus callosum up to the gyrus
hippocampi, which is at the medio-anterior end of the temporal lobe
and united there with F. rhinica posterior.
xii) F. corporis callosi (F cc)
It demarcates the upper margin of the corpus callosum and its
hinder part runs from the splenium along the medial border of thetemporal lobe to the uncus, where it continues to F. hippocampi.

T. KOJIMA

62xiii) F. subsplenialis '(F sbsp)
This nearly straight fissure'Jies oetween F .. splenialis and F. cor~poris callosi, and shows at the frontal end some asymmetry; on theright it is bent semicircularly around the genu corporis callosi, buton the left it begins from dorsal of the genu. On the medial surface
no fissure, which seems to correspond to the calcarine, was observed.
e) Anterior and basal surface (fig. 4 and 8)xiv) F. olfactoria (F ol)
It runs from the medial part of the ariterior F. rhinalis almost
parallel to the pallial margin, and behaves somewhat asymmetrically;on the right it lies medial to F. praesylvia, having few branchings,
while on the left it is lateral to this fissure and shows a longer coursewith many side branches. As previolisly mentioned, owing to absence. of the olfactory tract, the anterior F. rhinalis is not divided into twoparts, in- and outside.
The uncus is subdivided into three portions. by F. hippocampi andanother shallow sulcus in the medial part of the posterior F. rhinalis.
Till now I have related only comparatively well defined fissures,
while many others of more irregular, very complicated forms arepresent on the basal· temporal and occipital surface.
B)

Gyri

On the dorsal and lateral surface, bordered by the abo'\'>'e named':tiSsures, broad gyri are arranged concentrically around the posterior
end of F. sylvia in the following order, from the median margin of
the pallium to the Sylvi's fissure : G. medialis interna, G. medialis externa, G. ectolateralis, G. suprasylvius, G. sylvius inferior. Generally
speaking, those gyri show at their terminal parts very complicatedfigures pari passu with irregularity of the fissures. They show also
some notable asymmetries. The gyri, which border the obliquely directed
F. cruciata from anterior and posterior, must be called G. sigmoideus
anterior and G. sigmoideus posterior in analogy to the cases in carnivores. In the left hemisphere the G. medialis is divided on the posterior
surface into internal and external portions owing to the presence of a
distinct F. ectolateralis, while in the right such a division does nottake place.
On the medial surface there are G. submedialis and G. fornicatus
demarcated by F. suprasplenialis, F. splenialis and F. corporis callosi
etc. The G. fornicatus is narrowed remarkably when it extends aroundthe splenium and continues then. to G. hippocampi, terminating in a

On the Brain of the, Sperm Whale

63

swollen form (uncus). Besides we can see also G. dentatus and Fimbria
hippocampi behind the medial part of uncus.
Medial to the olfactory fissure lies on the anterior surface G.
rectus, which shows some differences between both sides owing to theasymmetry of F. praesylvfa. The configuration in the lateral frontal
surface is quite irregular.
A number of anatomists have hitherto. studied the fissures andgyri in the cetacean brains, especially GULDBERG worked on Balaenoptera musculus, Balaenoptera sibbaldi and Phocaena communis, RAWITZ
on Balaenoptera rostrata, RICHARD on Globicephalus melas, and TURNER
on Monodon and Balaenoptera rostrata, and the similarities to carnivores and ungulates have been very often acknowledged.
According to my own observation the fissures and gyri of theSperm whale are also similar to those of Mystacoceti, and of other
Odontoceti. But I met with following several points, somewhat different from the mentioning of the fore goers.
As to F. cruciata, LANGWORTHY slightly referred to this in Tursiops
truncatus, but no one has remarked its continuance to F. suprasplenialis.
In the Sperm whale I found F. suprasplenialis in direct connection
with F. cruciata.
The F. coronalis is very differently connected with other fissuresaccording to the kinds of animals, sometimes with F. suprasylvia, with
F. lateralis, or with F. cruciata, while its continuance to F. cruciata
has been reported neither in Cetacea nor in carnivores. Also in my
Sperm whale one hemisphere had two fissures probably corresponding
to it, but their direct connection with F. cruciata was not seen.
The presence of F. olfactoria in the Sperm whale is interesting,for it has not been reported in Odontceti, carnivores and ungulates.
It is likely that this fissure is present only in such animals as Primates,and Mystacoceti, which have the largely developed hemisphere and areat the same time microsmatic.
The direct continuance of F. corporis callosi to F. hippocampi is
not known in pig, cow, horse and baleen whales, though it occurs in
the elephant seal and man etc.; from this fact, considering also therelations previously mentioned of F. cruciata and F. coronalis, theSperm whale seems to have more similarity to carnivores rather thanto ungulates.
Two divisions of the uncus has been mentioned in some ungulates
and it forms wrinkles divided by several fissures in the polar bear,
while three divisions of it were found only in this whale.

T. KOJIMA

64

(III)

Cytoarchitecture of the cerebral cortex

1) Method. Materials fixed in formalin were cut into pieces of
1-3 cm thickness. Then by freezing 20-40 µ sections were prepared,
put in 90% alcohol or acid alcohol, containing 10% of concentrated
acetic acid and preserved about 24 hours in 37-38°C. After washingin water they were stained with 1 % thionin for about half an hour
at 40°C. Then they were washed in water again, and differentiatedin alcohol.
2) Resultsi) General observation
From various parts of the right cerebral hemisphere 38 pieces of
the cortex with underlying white matter were cut off at regular andabout equal intervals (1-8 of fig. 3, 4, 5, 6, 9 and photo A, B, C).
Compared with the cortex of other mammalia it is noteworthy inthis whale that the nerve cells are scarce and their differentiation in
6 layers is not fully developed.
Especially the development of the layers IV, V and VI is comparatively poor and in most places the layers IV and V are not well distinguishable from each other and so the cortex seems to have only 5cell-layers.
Each of the layers will be described in the following.
Layer I, Lamina zonalis :This layer is very inconstant in thickness (0.24-0.80 mm) ; the thickness is different also between top and sides of a gyrus.
Here a number of glia cells are dispersed and though scarce, smallround nerve cells are observed. Besides, though it is of great rarity, we
see sometimes large nerve cells of 10/30 µ (the largest diameter along
the cortical surface, the largest diameter vertical to the cortical surface)(9, 13). This layer is sharply distinguished from the next deeper layer.
Layer II, Lamina granularis externa :Of all layers this is the narrowest (0.08-·0.20 mm), but very densely populated with cells and clearly distinguishable; most of the cells
are either round granular or pyramidal, of the size 5/15-18/20 µ, andare arranged regularly. This layer is present in all places examined.
Layer III, Lamina pyramidalis externa :This is well discerned from the more superficial layer but its
border against the deeper layer is indistinct. Generally it ·is thick(0.4-0.6 mm), has scattered granular cells of various size (9/15-24/18 µ)and pyramidal cells exist in a larger number. The deeper within thisOn the Brain of the Sperm Whale65

layer, the larger become the cells, the form of which is mostly polygonal or triangular, though sometimes large round cells are also seen
and the density of them is different according to the places observed.
Layer IV, Lamina granularis interna:
The granular cells, whose presence characterizes this layer in othermammalia, are not especially gathered here. Though in the deeper
portion comparatively large cells are flocked together, I am not surewhether they really belong to this layer.
Layer V, Lamina pyramidalis interna:
The thickness (0.2-0.4 mm) is nearly constant in all places. Thereare comparatively large cells (about 18-24/30 µ) mostly of polygonal or
pyramidal form, and they are much crowded. In some places thislayer has giant pyramidal cells constituting a very clear layer, whilein other places, where no such cells are present, it is difficult to determine the border against the more superficial layers.
Layer VI, Lamina multiformis :It is 0.8-1.0 mm thick. Here are scattered relatively large pyramidal, round or stellate cells of 18-24/30-24 µ and many other forms.
ii) As the next step I tried to know the structural localization of
the cortex, examining, if any, the peculiarity of each plac~.
a) Anterior and dorsal surface (1-4 of fig. 4, 3-20 of fig. 3,
photo. A and B)
Giant pyramidal cells are present from the lower end of G. rectus
to the anterior part of G. medialis on the dorsal surface and up to
the frontal part of F. ectolateralis on the lateral surface. Especiallyon and near G. sigmoideus (5, 9, 8, 14) most of them are gathered.
It reminds us of area 4 (praecentralis gigantopyramidalis) of BRODMANN.
Further backward as well as foreward they become sparse.
At G. sigmoideus posterior (9) cells increase in number and forma clear layer in the deeper portion of the layer III (IV?). Further
backward at G. medialis interna (13) this layer becomes indistinct.
Still further back near the occipital pole (17, 18) no giant pyramidalcells are found in the part corresponding to the layer IV (V ?) but
relatively large granular cells are present forming a sheet.
At G. rectus (1) and near the frontal pole (3, 4) the layer IV canbe observed only with difficulty and the layer II becomes thinner. On
the whole, nerve cells of the cortex are few in number and giant
pyramidal cells are shrunken to angular forms.
The anterior part of G. ectolateralis (3, 4) is similar in structure

T. KOJIMA

66

F ectlF ectl

F sp
Fco?

F ssp

Fol

Fig. 11. Distribution of giant pyramidal cells in the right cerebral hemisphereof Physeter: The dots represent the cells in question

to G. sigmoideus, though the number of nerve cells is here somewhat
less. G. suprasylvius contains no giant pyramidal cells.
From these observations I came to the opinion that the places,
where giant pyramidal cells are present, probably representing the
motor area, are in the Sperm whale not restricted within narrow limits
but extend widely in the hemisphere.
They are most abundant on the anterior and posterior sides of G.
sigmoideus, and dispersed both towards frontal and occipital. Also in
the layer IV (V?) cells tend gradually to become dense from F. cruciata backward. The layer II becomes thinner in the frontal part andcells decrease in number, as we go more frontal. But further backthan F. cruciata scarcely any change occurs. Generally speaking, cells inall layers tend to increase in number as we examine further backwards.
b) Posterior surface (26, 27, 28 of fig. 5, photo. B 27)
Three places near the occipital pole were studied, with the resultthat cells are numerous here, especially in the layer IV (or V) they

On the Brain of the Sperm Whale67

are abunda,,Ylt and large in size. This finding reminds us of the striatearea, though it was impossible to observe macroscopically neither the
intracortical white stria nor the calcarine fissure.
c) Lateral surface (21-25 of fig. 6, photo. B 23)
Both of the superior and inferior G. sylvius and a part of G. suprasylvius were studied. In the antero-dorsal part of G. sylvius superior
no giant pyramidal cells are present, while they appear on the lateralbasal part of this gyrus and the cells are generally larger.
In the f3Uperior and inferior G. sylvius giant pyramidal cells areseen here and there, and cells of the layer III are also comparatively
numerous.
d) Medial surface (28-37 of fig. 9, photo. B 29, C 30, 32)
G. submedialis, G. fronicatus and G. hippocampi were examined.
The upper frontal part of G. submedialis (30) has densely arranged
giant pyramidal cells, and the layers II and III are thick, having manycells. This part resembles G. sigmoideus posterior.
In the postero-basal part (33) many large round cells are assembled
in the layer IV (V). Further lower (35) this layer shows middle sizedpyramidal cells.
In G. fornicatus (29) each layer, is narrow and in the layer V large
round nerve cells are gathered densely, forming a special sheet.
G. hippocampi (32, 34, 37) has a quite particular structure; thatis, the layers II and IV are thick and crowded with cells. Most cellsof the layer IV are polygonal or pyramidal. In the extremely thinlayer III small cells are scattered.
Uncus (38 of fig. 4, photo. C 38) is of an extraordinary cytoarchitecture; here only 3 layers are discerned, the first layer of which
resembles the layer I of other regions and the second layer, though
not very much different from the layer II of other regions, is comparatively thick and has many cells. The third layer contains very
few cells of round or pyramidal form.
Considering the colossal bulk of the cortex and the very complicatedfissures and gyri of the cetacean cerebral hemisphere, it must be of.
much interest to know the cytoarchitecture especially its difference
according to regions. Though I desired at first to make a map upon
the structural differences of the whole cortex, the fulfillment had tobe postponed to a later occassion, for the present study was limited
to only 38 places in one hemisphere. Meanwhile my object was directedto the determination of cortical regions, which might correspond to
the so-called motor area, to the striate aera 1 o~ to the superior tern-

68

T. KOJIMA

poral area of the human brain, but the result is yet far from success,for the macroscopical orientation of these places is very difficult andmoreover the cytoarchitecture of the cetacean cortex is very insufficiently differentiated.
Till today the cerebral cortex of the cetacea has been histologicallystudied by' several authors, among whom MAJOR'S work on Balaenoptera
musculus, RAWITZ's on Balaenoptera rostrata and Phocaena communisand LANGWORTHY's on Tursiops truncatus are worthy of special reference.
MAJOR observed quite in details the cytoarchitecture at several
places chosen from Gyri sylvius, suprasylvius, ectosylvius and medialis,and stated consequently· that the frontal lobe is quite similar to thetemporal lobe, while the occipital lobe only is a little different in
structure as the cells are here smaller. Besides, the cells are pyramidal in the layers I, II, III and the layer IV is not clearly discriminated, while the layer V consists of spindle cells. Chronologically
MAJOR'S report is previous to BRODMANN's famous work on the localization of the cerebral cortex, and so it did not tell about the formationof 6 cell-layers.
In my opinion, the layers IV a~d V of MAJOR, are of much doubtful
existence, and as giant pyramidal cells were seen in the deeper portionof the layer III in his classification, which I believe is corresponding
to our layer V, I can not agree with MAJOR, so far as he said
that the layer III has pyramidal cells, as I observed there round andpolygonal cells too. As to the fact that in the frontal lobe and in
the temporal lobe giant pyramidal cells are extensively observable, I
agree with him (fig. 11).
RAWITZ examined only three parts of the cetacean cerebral cortex
and stated that it is of a primitive, quite unusual structure, and that
there is no differentiation of cell layers as seen in other mammals.
LANGWORTHY researched 16 places quite minutely. He discussed
much on the thickness of the layer I, though he did not refer to the.conditions of fixation. Deeper than the layer II he named each layer
as supragranular, granular, infragranular, and polymorphic. He tried
to determine motor area, sensory area, striate area and temporal area
as in other mammalia, but he did not seem to have minded muchabout the complicatedness of the gyri, and identified F. cruciata, F.
calcarina and other fissures relatively easily, and spoke even the physiological function of these areas. I endeavoured to compare LANGWORTHY' s observations on the "striate area" of his nomination to myOn the Brain of the Sperm Whalefindings in the cortical region, which looks macroscopically like corresponding to his (36 of fig. 9) and further :on another place of the occipitalpole (27), and found that cells of the layer IV are increased the mostnoticeably in (27) than in the "striate area" of LANGWORTHY.
One point, in which I agree completely with him, is as also with
MAJOR, that giant pyramidal cells exist quite in wide areas beginningfrom the anterior end of the frontal lobe.
It is a much discussed problem, which fissure in other mammalia
the central fissure of Primates corresponds to. And most of the previous
authors have identified it either with F. cruciata, with F. praesylvia
or with F. coronalis, etc. BYCHOWSKY took F. coronalis for it on thehistological basis, that in front of this fissure giant pyramidal cells
are found while they are absent in the posterior. In the Sperm whale
I can not find such a fissure as showing a clear borderline upon thehistological structure. I want to say only that giant pyramidal cells
are present the most densely in F. cruciata; it seems to be the centreof their existence (fig. 11).
As to the division of the whole cortex into granular and agranular
ones which EcoNOMO tried and recently BAILEY reported in the humanbrain, I can't say anything definite in the Sperm whale, because thelayer IV is not well differentiated and moreover my microscopicalobservations are limited to only a relatively few cortical localities.
But so far as my own results are concerned, the granular cortex exists
near the occipital pole, on G. sigmoideus posterior and on the laterobasal portion of G. suprasylvius and on G. sylvius etc., while theagranular cortex is seen anterior to F. cruciata and in the antero-dorsal
portion of F. ectolateralis. And further to determine the gigantopyramidal area within the agranular cortex was impossible as the gianpyramidal cells are so extensively distributed in the cortex of theSperm whale, as I stated _above.
ResumeFollowing observations were made on the brain of the Sperm whale
caught in the Antarctic Ocean.
1) The average brain weight of 16 male whales (body length of
46-54 feet) is 7.8 kg, that is heavier than that of Mystacoceti (over 50feet).
The ratio of the brain weight (kg) to the body length (feet) is
0.154 as average and this ratio seems to decrease in senility.

70

T. KOJlMA

2) Measurement and macroscopical study on the brain of a Spermwhale (50 feet long)a) The ratio of the sagittal axis to the transversal axis is 0.822:
1 ; that is extremely brachycephalic.
b) The olfactory bulb and tract do not exist.
c) The cerebral peduncle is divided in two parts and the tractus
peduncularis transversus is present.
d) . On the ventral surface of medulla oblongata
small pyramidal
I
tracts are seen.
e) F. cruciata continues directly to F. suprasplenialis.
f) Differently from Mystacoceti, F. rhinalis is not divided into
two, medial and lateral, parts.
g) F. corporis callosi is continuous with F. rhinalis posterior.
h) F. olfactoria is present.
i) Uncus js divided into three parts by two shallow sulci.
3) Cytoarchitecure of the cerebral cortexa) The formation of 6 layers is not clearly observed. As it isdifficult to discriminate between the deeper portion of the layer III
and the layers IV and V, it seems that only 5 layers exist.
b) Giant pyramidal cells are found quite extensively from thelower end of the frontal lobe till the anterior part of G. medialis,
spread on the outside from the anterior part of G. ectolateralis andon the inside till G. submedialis. Especially in G. sigmoideus anterior
and posterior they are the most densely gathered.
c) In the vicinity of the occipital pole the layer IV (V ?) becomes thicker, having more and larger cells. ·d) In the frontal lobe cells of each layer decrease in number,as one observes more forewards.
e) Though it is difficult to divide the cortex into granular andagranular ones, in generai F. cruciata seems to show the borderline,
for further anterior from this the cortex becomes more agranular,
while further posterior it gets more granular.
It is a pleasure to record my indebtedness to Prof. T. Ogawa forhis constant guidance and encouragement. My thanks are also due toAss. Prof. T. Kusama for help and advice on various aspects of thissubject.

On the Br:J.in o:f the Sperm Whale

Literature
1) Addison, W. H. F~: On the Rhinencephalon of Delphinus delphis, L. J. Comp.
Neurol. Vol. 25, 1915.
2) Bailey, P.: On the Organization and Function of the Cerebral Cortex. Brain and
Nerve. Vol. 2, 3. 1950.
3) Brodmann, K.: V ergleichende Lokalizationslehre der Grosshirnrinde. 1901.
4) Bychowsky, G.: Zur Frage der Homologie des S. coronalis canidae und des S.
centralis der Primaten. Zsf. f. Anat. u. Entwg. Bd. 89, 367, 1929.
5) Economo, C. v.: Zellaufbau der Grosshirnrinde des Menschen. 1927.
6) Guldberg, G. A.: Ueber das Zentralnervensystem der Bartenwale. 1885.
7) Langworthy, 0. R.: A Description of the Central Nervous System of the Porpoise (Tursiops Truncatus). J. Comp. Neurol. Vol. 54, No. 2, 437, 1929.
8) Miller, G.: The Telescoping of the Cetacean Skull. Smithsonian Miscellaneous
Collection. Vol . 76. 1923.
9) Major, H. C.: Observation on the Structure of the Brain of the White Whale(Delphinapterus Leucas). J. Anat. and Physiol. Vol. 8, 1879.
10) Papez, J. W.: Comparative Neurology. 1929.
11) Rawitz, B.: Das Zentralnervensystem der Cetaceen. III Die Furchen und Windungen des Gehirns von Balaenoptera rostrata, Fabr. Arch. f. mikr. Anat. Bd.
75. 225. 1910.
12): Zur Kenntniss der Architektonik der Grosshirnrinde des Menschen undeiniger Saeugetiere. III. Die Hirnrinde von Schwein, Pferd, Zahnwal, Bartenwal, Beutelratte. Zsf. f. Anat. u. Entwg. Bd. 82, 131, 1927.
13) Richard, M. J.: Resultats compagnes scientifiques. Fascicule XXXI. 1905.
14) Turner, W. M.: The Convolution of the Brain. A Study in Comparative Anatomy. J. Anat. and Physiol. Vol. 25, 105, 1870.
15) Flower, W~ H.: On the Osteology of the Cachalot or Sperm Whale (Physeter
macrocephalus). Trans. Zool. Soc. Londen. Vol. 6, 309-372, 1867.

T. KOJIMA

72

Abbreviation for all figures
A ol .......... Area olfactoria
C tr ......... Crus cerebri
Ge cc ........ Genu corporis callosi
01 ........... Olive
P ....... , .... Pons
Py .......... Pyramidal tract
Sp cc ........ Splenium corporis callosi· U ............ Uncus gyri hippocampi
II ............ Fasciculus opticus
V ............ N. trigeminus
VII. ......... N. facialis
VIII ......... N. statoacusticus
F co ......... Fissura coronalis
F er ......... F. cruciata
F cc ......... F. corporis callosi
F ectl ....... F. ectolateralis
F ects ....... F. ectosylvia
F h ....•..... F. hippocampi
F it ......... F. interhemisphaerica
F 1 .......... F. lateralis
F ol ......... F. olfactoria

F pr ......... F. praesylvia
F rh a .....•. F. rhinica anterior
F rh p ....... F. rhinica posterior
F S .......... F. sylvia
F sp ......... F. splenialis
F ssp ........ F. suprasplenialis
F, ss ......... F. suprasylvia
G ectl. ...... Gyrus ectolateralis
G f .......... G. fornicatus
G h .......... G. hippocampi
G m ......... G. medialis
G m i ....... G. medialis interna
G m e ....... G. medialis externa
G r .......... G. rectus
G sig a ...... G. sigmoideus anterior
G sig p ...... G. sigmoideus posterior
G sm ........ G. submedialis
G ss ......... G. suprasylvius
G sy s ....... G. sylvius superior
G sy i. ...... G. sylvius inferior

1

9

'

;~

VI

v

IV?

III

II

>

;'}

13

IV, ViIII;~,~~;;~~i-- II

Photo. A .... Cell layers of the cerebral cortex (1, 5, 9, 13) of Physeter.

5

VI

v

IV, V?

IIII

. '"'

30

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..~'·ir:.''\·~'··.,. . ·'. "·'\.._'~~~~ '4~i,,: :~i!~ ".' ~ ~' "'~ .,,..~ '· )""., ~,.III
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first layer·'' second layer
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38

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Photo. C•... Cell layers of the cerebral cortex (30, 32, 38) of Physeter.

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