OBSERVATIONS ON THE SPINAL CORD OF THE
RIGHT WHALE
YASUSHI SEKI*
The spinal cord of a female Eubalaena glacialis captured on May 23rd,
1956, off Kinkazan, was investigated morphologically. The body length
measured 11.65 m (38 feet 4 inches). The spinal cord was removed twodays after the capture (May 25th) and fixed in formalin. After measuring, photographing and macroscopical observations, it was cut in eachsegment corresponding to the spinal nerve roots. For microscopical studies
they were refixed then in Muller's solution for 2 weeks in 37°C, imbedded into celloidin, sectioned transversely or longitudinally and stainedwith Pal-carmine method, hematoxylin-cell-staining method and MassonGoldner's method**.
RESULTSGROSS ANATOMY OF THE SPINAL CORD, THE SPINALNERVE ROOTS AND THE MENINGES

Following measurements were done outside of the vertebral canal, so thatthe spinal cord might be somewhat contracted from the natural state of
the cord. After Hosokawa, this contraction rate is 2 to 3 per cent of
the total length of the spinal cord.
The total length of the spinal cordea. 174 cm,
Cervical cord (consisting of 8 segments)
ea. 23 cm,
Thoracic cord (,,14 segments)
ea. 105 cm,
Lumbal cord(,,
10 segments)
ea. 36 cm,
Coccygeal cord (,,8 segments)
ea. 10 cm.
It is remarkable that the spinal cord is very short (17 4 cm) for the
body length (11.65 m). The cord length ratio for the body length is
14.9 % , while that of the matured fin-whale is said 24.3% (Hosokawa).
There are in all 40 segments in the spinal cord, though the total number of the vertebral bones of the Eubalaena amounts to 56 or 57. Of
course, the spareness in number of the segments in the cord is causedby shortening of the coccygeal cord (8 segments in the coccygeal cord

* Department of Anatomy, School of Medicine, University of Tokyo. Formerly Institutefor Brain Research, University of Tokyo.
** Many thanks are due to Miss T. Koide, Miss T. Ogisaka and Miss M. Suda, techni·
cians in the Institute for Brain Research, for their great efforts to manufact the microscopi·
cal preparates.
231

232

Y. SEKIagainst 25 or 26 of the coccygeal vertebrae). None of the spinal nerve
root is recognized below Co. 8. The caudal end of the conus medullaris
is seen ea. 1 cm below the caudal border of the radix of Co. 8. The
lower border of the dural sack is found at nearly the same level withthe caudal end of the conus medullaris; thus the :filum terminale internum is difficult to see. The filum terminale externum i.e. the portionof the filum mantled with the dura mater, runs farther caudalward.
At most levels of the spinal cord, the points where the dura materis penetrated by the spinal nerve roots are not so far distant from theplaces where the :fila of the roots are connected with the cord. The
cauda equina can not be recognized inside the dura mater. The internallamina of the dura is markedly thick (3 mm in the cervical roots portion,
2 to 3 mm in the thoraco-lumbal roots portion and 1.5 to 2 mm in thecoccygeal roots portion), and outside this membrane, there is a very
wide epidural space filled with extremely rich blood vessels and fatty
tissue. After penetration of the dura, the radices descend side by sidemaking epidural cauda equina, and reach the corresponding intervertebral
foramina. There the radices of the lower thoracic, the lumbal and thecoccygeal nerve roots have to run in the epidural space for very long
distance (for several meters). In the subarachnoidal space i.e. between
the arachnoid and the pia mater, many blood vessels are seen, too.
They are chiefly made of arterial network, with fine and dense arachnoid
trabeculae, surrounding the surface of the spinal cord. In Fig. 1, an
EXPLANATION OF FIG. 1
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.

Pons Varoli, Medulla oblongata, C. 1, 2 and 3.
from C. 4 to Th. 2.
Th. 3.
Th. 4.
a little part of Th. 4 and uppermost part of Th. 5.
a little part of Th. 5 and uppermost part of Th. 6.
a little part of Th. 6 and upper two thirds of Th. 7.
lower third of Th. 7 and uppermost part of Th. 8.
a little part of Th. 8 and upper two thirds of Th. 9.
lower third of Th. 9 and upper two thirds of Th. 10.
lower third of Th. 10 and Th. 11.
The 12 and upper half of Th. 13.
lower half of Th. 13 and Th. 14.
L. 1, 2 and upper two thirds of L. 3.
lower third of L. 3, from L. 4 to L. 6 and upper two thirds of L. 7.
lower third of L. 7, from L. 8 to Co. 5 and upper half of Co. 6.
lower half of Co. 6, Co. 7 and 8, lower end of conus medullaris and filum
terminale.
Th: Thoracic cord
C : Cervical cord
Co: Coccygeal cord
L: Lumba! cord

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234

Y. SEKI

external view, the cervical enlargement is clearly visible; however, thelumbal one is hardly to recognize. Table 1, showing the thickness ofthe spinal cord, indicates the same also.
TABLE 1.

THICKNESS OF THE SPINAL CORD (diameter in mm)

Transverse
15.0
15.0
17.0
17.5
17.0
13.0

c

1
4
6
8
Th 2
5

Ventro-dorsal
14 0
14.0
16.0
14.0
15.0
13.0

Th 10
14
3
L
7
Co
5

Transverse
13.0
12.5
13.5
13.0
12.5
8.0

Ventro-dorsal
13.5
12.5
12.0
11.0
10.0
7.0

DIMENSION OF THE CROSS SECTIONS OF EACH SEGMENTIn Fig. 2, our measurements on the extent of the cross section area of
each segment are indicated by curves. They are acquired from thecelloidin sections stained by Pal-carmine method. In the curves denoting
the entire area and the white substance, the cervical enlargement isshown clearly, but the lumbal one not distinctly. In the curve presenting
the gray substance, both the cervical and the lumbal enlargement are
CC8)

Th (14)

L(/Q)

mm 2

200•1------1''-\--l--~~~~~---.~~~~~~-r-~~~~-t--r\·-------------··--·----···-···--·----·--··--··-·--·--·---············ .......--···············~ \.::'.
Fig. 2. Curves showing the variations in sectional area of the graysubstance ( · · · · ), the white substance (----) and the entire area( - ) in each segment of the spinal cord.
recogniz~dmoderately. It is significant that the maximum extent of thelumbal enlargement is found not in the lumbal, but in the coccygeal
level, which results perhaps from the formation of the huge tail (notthe flukes) of the cetacea. Guldberg (1885) described the lumbal enlargement in embryos of some Balaenopterae, Cunningham (1877) observed

OBSERVATIONS ON THE SPINAL CORD

235

it also in matured Phocaena, though, as a rule, the lumbal enlargement
has not been definitely recognized in the cetacea. In our material an
external view, the lumbal enlargement is not so clearly developed, but
gray substance in the same levels are doubtless expanded.
ANTERIOR COLUMN

The anterior columns are developed well, even in the thoraic level,
occupying nearly half of the total gray substance in the cross section.
At the levels from cervical to upper thoracic (cervical enlargement) andfrom middle lumbal to upper coccygeal (lumbal enlargement) cord, thegray substance is occupied over half by the anterior column (Fig. 3-13).
In the cervical enlargement the anterior columns are developed verymuch to the lateral direction; on the contrary, in the lumbal enlargement
the anterior columns are larger in the ventrodorsal extent than in thetransverse one. It is said that the motor cells innervating the musculature of the extremities are situated in the lateral part of the anterior
column, and so it seems quite natural, that they are poorly developedin the lumbal enlargement of the Eubalaena.
Most of the cells of the anterior column are deeply stained with carmine or hematoxylin, large sized and polygonal shaped; among theselarge cells there are also small sized, triangle, spindle or polygonal shaped,
scattered cells. Moreover, we find light coloured, somewhat roundishpolygonal or spindle shaped, large or medium sized (50 to 100 µ) cells,
situating at the medial and lateral periphery and the dorsal part of theanterior column, sometimes as a few scattered cells among the deep
coloured polygonal larger cells of this column. Majority of them areseen in the cervical, lower lumbal and coccygeal levels ; they are rather
scanty in the thoracic and upper lumbal cord. Hatschek (1896) describedchromophobe cells in the anterior column of the common dolphin (Delphinus delphis), but it is not clear that they correspond or not with thelight coloured cells we found. He noted the chromophobe cells are in
number over that of the chromophile cells in the lumbal cord ; but they
are never so in our material. In the thoracic and upper lumbal levels,the light coloured cells are only of small amount; on the other hand,as later mentioned, the lateral horn cells are very well developed in thesame levels ; in addition, as most of these cells exist in the neighbourhood of the pars intermedia, we supposed that the cells might be associated with some autonomic function.
When we examine the cells of the anterior column in longitudinallysectioned preparates, most of their long axis are parallel with that of
the spinal cord in the thoracic levels, but not always just so in the236

Y. SEKI

cervical or the lumbo-coccygeal levels mingling here with cells extendedin oblique or transverse plane.
Is it true that the cells in such giant sized animals as the Eubalaena
are larger than the cells in man ? In Table 2, the sizes of the cells are
TABLE 2. CELL SIZE OF THE ANTERIOR COLUMN(measurements of 100 cells in each level)
Eubalaena gracialis
C6
Th 8
Co 1

Average (µ)
56 x 2144 x 1694 x 36

Maximum (µ)
69 x 46
69 x 29
171 x 69

Minimum (µ)
17 x 623 x 640 x 11

Average (µ)
46 x 1630 x 1348 x 25

Maximum (µ)
93 x 37
57 x 2097 x 40

Minimum (µ)
17 x 1111 x 619 x 7

Homo sapiens
C6
Th 8
L4

indicated concerning the anterior columns of Eubalaena and man. The
human cells seem somewhat smaller than the cetacean cells but not so
distinctly in the cervical or thoracic level; however, in the lumbal enlargement, the cetacean cells are doubtless much larger than those ofman. In man, the differences of the cell size between the cervical, thethoracic and the lumbal level are not so remarkable, while in the cetacea,
the cell size in the coccygeal level is conspicuouly larger than those in
the other levels. From the data as above mentioned we considered thatthe size of the nerve cells seems more related to the length of the nerve
fibers originating from them than to the body size of the animals ; inthe Eubalaena the spinal nerves in the lower levels have to run for very
long distance.
The anterior roots appear at a wide range of the anterior surface ofthe cord, extending from the anterior to the lateral funiculus. Some ofthem start even in the anterior median fissure (Fig 8).
POSTERIOR COLUMNAt almost all levels, the posterior columns are far less developed than
the anterior columns on the same section, especially so in the middle
cervical, the whole thoracic, the lower lumbal and the upper coccygeal
cord. The poor development of the posterior column in the cetacea waspreviously described by many authors (Guldberg 1885, Hatschek 1896,
Sano '09 usw.). In addition, the border of the gelatinous substance ofRolando looks not so distinct in most levels of the cord. The same results were mentioned by Hatschek (1896) in Delphinus delphis and by

OBSERVATIONS ON THE SPINAL CORD

237

Sano ('11) in Delphinus tursio ( =Tursiops truncatus), and these wereconsidered chiefly due to less developed cutaneous sensibility and lackof the hair in the whales (Kappers '36).
At C. 1, however, the posterior column is moderately large assuming
nearly the same size as the anterior column at the same level. Morerostrally, in the medulla oblongata, the spinal root and its nucleus of
the trigeminal nerve are very well developed, and the lower extensionof this nucleus reaches down to the level of C. 1 (Fig. 3, 14, 15). It is toconsider that the Eubalaena has a great many sensory organs in the skinor the mucous membrane of the head portion. In fact, in our laboratory,
Ogawa and Shida recently confirmed the existence of structures, which
seem to be sensitive apparatuses having rich nerve endings, in the lips,
tongue, palate and basis of the mouth cavity of the Eubalaena. The presence of these structures must be related to the marked developmentof the trigeminal sensory nuclei in the central nervous system.
The postero-marginal cells are developed well in the cervical or especially in the lumbo-coccygeal, but less in the thoracic levels in the zonaspongiosa of the posterior column. Their size are 15 to 50 µ in thetransverse, 15 to 120 µ in the longitudinal direction. Namely, most of
their long axis are directed longitudinally.
The nucleus proprius of the posterior column is chiefly composed ofsmall sized (5 to 20 µ) spindle shaped cells and medium sized (10 to 40 µ)polygonal or somewhat rounded cells, and the long axis of the former
are directed longitudinally and measured up to 30 µ. In the lumbococcygeal levels they contain sometimes the typical cells of the Clarke's
column.
It is peculiar that the posterior columns of both sides come to adhereon the midline in the lower half of the thoracic and the coccygeal cord.
(Fig. 8, 13).
CLARKE'S COLUMNThe Clarke's columns of the Eubalaena are well developed in the thoracolumbal levels, but it is not easy to determine their upper and lower
limits, as in the cord more cranial or caudal than the portion above
mentioned, there are also a few cells at the same position. It is especially so in the upper cervical cord, where the cells in question represent
possibly the cervical nucleus of Stilling ; on the other hand, some of quite
the same type of Clarke's cells are seen not only in the lowest lumbal
levels but also in the whole coccygeal cord. The caudal extension of
the Clarke's column is well known in the spider monkey (Chang '51),
and we meet here with the resembling structure in the Eubalaena ; it238

Y. SEKI

deserves attention, that both animals have very well developed tails.
At the levels from lowest thoracic to middle lumbal cord, the Clarke's
column shows its maximum development, and it is composed of some cellgroups, involving many large, roundish nerve cells (20 to 90 µ). Mostof these cells are directed longitudinally and their long axis are measured
up to 180 µ, but some cells appear round still in longitudinal sections.
Our noteworthy finding is the fusion of the dorsal cell groups of bothsides on the midline, but the ventral cell groups are separated fromthe contralateral ones at the same levels (Fig. 8, 9, 10). Dexler ('11) in
Halicore dugong, Hatschek (1896) and Schacherl ('02) in Delphinus delphis,
mentioned also the fusion of the Clarke's column on the midline.
PARS INTERMEDIA

In comparison with the spinal cord of other mammals, the territory
occupied by the intermediate zone is moderately wide in the Eubalaena
and there we see a great many nerve cells and a large amount of nerve
fibers. Because of the well developed gray commissure, in most levelsof the cord, the dorsal funiculus are far distant from the anterior funiculus. These findings upon the pars intermedia, suggest certain functional (especially of autonomic nature) differences of this part between
the cetacea and the other animals.
On the transverse sections, the anterior white commissure in thethoracic levels are hardly recognized, but on the longitudinally sectioned
preparates, many fi.bers are crossed in the thoracic cord making small
angles (5° to 10°) to the median plane. On the other hand, in thecervical or lumbo-coccygeal levels, the anterior commissural fibers areclearly seen on the transverse sections. Hatschek (1896) noted also thecharacteristic anterior white commissure extended in the sagittal direction in the dolphin.
The nucleus of the lateral column is recognized in the levels from D.
1 to L. 8, showing the group of middle sized (20 to 60 µ), roundish or
spindle shaped cells in the light coloured gray substance at the lateralborder of the intermediate zone. In most heights, this column makes
the lateral horn protruding into the lateral funiculus (Fig. 7, 8, 9, 10).
Takahashi ('13) mentioned the gelatinuous substance in the lateral horn
nucleus ; and in our material, just the same findings are obtained.
The reticular formation is well developed in C. 1 ; it is represented
by many scattered cells at the part adjacent to the lateral border of theintermediate zone and in the neighbouring white substance of the lateralfuniculus. In C. 2, it is similarly found but a little less developed thanin C. 1. At the other levels of the cord, the cells in question are far

OBSERVATIONS ON THE SPINAL CORD

239

poorly developed than at C. 1 and 2; only a few cells are seen in thedorso-lateral border of the intermediate zone and sometimes also in theneighbouring white substance.
It is a peculiar finding that the central canal is completely obliterated
at any level of the cord. Although the border of the central gelatinous
substance is considerably distinct in the upper portion below the obex
and also in the coccygeal levels, traces of the ependymal cells are nowhere to be recognized. Hatschek (1896) in Delphinus delphis, Biach('06) in Phocaena communis, described also that the central canal was
fully obliterated. In man, the central canal of the spinal cord is in theadults often closed and changed into a cord-like structure formed by theremaining ependymal cells. Biach ('06), however, noted an opened
central canal in the lower portion of the spinal cord in Delphinus tursio.
ACCESSORY NERVE ROOTSIn the Eubalaena, the spinal roots of the accessory nerve are very poorly
developed, and only in the lst cervical level. They are recognized there
as few fascicles consisting of a small number of thick fibers. Thisfinding is contradictory to the description Hatschek's (1896) that the
spinal root of the accessory nerve was observable as 1' Respirationsbtindel '' of Krause until the level of the cervical enlargement. On theother hand, the accessory nerve roots are developed well in the lower
portion of the medulla oblongata of the Eubalaena.
At C. 1, the lateral part of the anterior column makes a somewhat
reticular appearance protruding into the lateral funiculus, where groupsof deeply stained, large sized polygonal cells are present. When wefollow it up to the medulla oblongata, this structure separates graduallyfrom the anterior column, and makes independent and beaded cell islands
extending longitudinally. At the lower level of the rhomboid fossa,
these islands become larger in the lateral funiculus and continue directly
to the nucleus ambiguus (Fig. 3, 14, 15). Namely, in the Eubalaena, it isconfirmed that the lower extension of the nucleus ambiguus is fused
into the lateral part of the anterior column in the lst cervical level.
From this lower extension of the nucleus ambiguus, perhaps some partsof the bulbar roots of the accessory nerve take origin.
Ogawa and Chen ('47) remarked the lower extension of the dorsal
vagal nucleus continuing to the medial border of the lateral funiculusof the lst cervical level in some ungulates. The same facts were confirmed also by Mannen and Seki ('58) in some pinnipedia. However, in
the Eubalaena, a similar finding is not obtained.

240

Y. SEKI
NUCLEUS CERVICALIS LATERALIS

Rexed and Brodal described the lateral cervical nucleus in the cat('51) ; the corresponding cell groups are seen also in the lst cervical
cord of the Balaena (Fig. 3). They are found in the dorso-medial partof the lateral funiculus as a spindle, oval or irregularly reticular shaped
gray substance, having middle sized (20 to 35 µ) roundish and somewhat
deeply stained polygonal cells. It shows no sharp limit to the medial
situating reticular formation. This nucleus changes its shape and largeness from section to section, and sometimes disappears on one side.
The upper limit of this nucleus is in the lowest level of the medulla
oblongata, while caudalward it is present, though less distinctly, untilin the 2nd cervical level.
PYRAMIDAL TRACT

The pyramids are fiat assembly of bundles of longitudinally running thinfibers, which lie on either side of the midline at the ventral border ofthe medulla oblongata (Fig. 15). At the lower levels of the medulla
oblongata, the pyramidal tracts of both sides come to fuse together andmake a wedge-shaped unpaired white substance area between the anterior
funiculi of both sides (Fig. 14). More caudalward, the pyramid, decreasing
the quantity of its fibers, changes into a spindle shaped tract and its
location shifts slowly to dorsal and reaches then in the lst cervical level(Fig. 3). During the course above noted almost all fibers of this tract
remain seemingly in the longitudinal direction, so that the decussation of
the pyramidal fibers is very hard to recognize.
However, in the upper levels of the hypoglossal nucleus, we see somefiber bundles, which are mediated between the medial parts of the
pyramids of both sides (Fig. 15), but we can not yet ascertain the decussation i.e. the interchange of the ft.hers of the pyramidal tracts. In thelower level of the medulla oblongata, most fibers of the pyramids are stiluncrossed.
At the lst cervical cord, the pyramidal tract appears on the midline
as a spindle shaped longitudinal bundle, which decreases gradually its
dimension, and then it disappears in the 2nd cervical level.
Neither in the medulla oblongata nor in the spinal cord, we can trace
further course of the pyramidal fibers branching off from their maintract.
Rawitz ('09) and Gans ('16) in Phocaena, and Matsumoto ('53) in Cogia
breviceps and Berardius bairdii, described the pyramidal decussation,
but some previous authors could not confirm it (Hatschek and Schlesinger'02, Wilson '33, Jelgersma '34 usw.). We have to examine further theOBSERVATIONS ON THE SPINAL CORD

241

preparates sectioned parallel to the long axis of the medulla oblongata,in order to determine the problem whether the pyramidal decussation
exists or not in the cetacea.
The pyra~idal tracts of the Eubalaena are composed chiefly of very fine
medullated nerve fibers, showing light coloured area in the myelinstained preparates sharply contrasted to deep coloured neighbouring whitesubstances.
POSTERIOR FUNICULUS AND ITS NUCLEI

Hatschek (1896) described in the dolphin the posterior funiculus as abundle, in which the posterio_r median septum is dismissed. In the
spinal cord of the Eubalaena, we see no definite posterior median septum
on most sections of the thoracic and cervical levels except at C. 1, but
in the lumbo-coccygeal levels the septum is clearly visible. The border
between the Goll's and Burdach's funiculus is not definitely recognizedeven in the upper cervical levels.
At the levels beneath the obex, because of the disappearance of theposterior median septum and the neighbouring fibers in the posterior
funiculi, the Goll's nuclei of both sides come to adhere on the midline(Fig. 14), and in the levels upper to the obex, of course, they are separated again.
The lower extensions of the Goll's nucleus of both sides are fused
together in the Bischoff's nucleus in the lowest level of the medulla
oblongata. The Bischoff's nucleus is situated on the midline of theposterior funiculus in this level and sometimes also in the lst cervical
cord (Fig. 3), and has been considered as remarkably present in the
animals which have a well developed tail. In the Eubalaena, however,this nucleus is not so large developed.
FIBER TRACTS IN THE WHITE SUBSTANCE OF THE SPINAL CORD

fo our preparates of the spinal cord of the Eubalaena, any long fiber
tract is not certainly traceable in the ventro-lateral funiculi. But only
the areas corresponding possibly to the dorsal spino-cerebellar tract of
Flechsig are seen at the dorsal margin of the lateral funiculi of bothsides. These areas are composed of many large nerve fibers (10 to 15 µ),
begin at the lowest level of the cord, and show deeply stained zone insections of the lower thoracic and the lumbo-coccygeal cord, but they
are hardly to distinguish from neighbourhood in the upper thoracic andthe cervical level. In the levels from C. 1 to the medulla oblongata,
they appear clearly at the same position as deep coloured areas.

242

Y. SEKISUMMARY

The results of macroscopical and microscopical observations upon the
spinal cord of female Eubalaena glacialis are summarized as follows :1. The length of the spinal cord is very short (14.9% of the bodylength). The cauda equina is not present inside the dura mater, but
exists only. in the epidural space, where we see also extremely rich bloodvessels and fatty tissue. Externally, the lumbal enlargement is notdistinctly seen, but in the curve indicating the dimension of the graysubstance of each level in the cross section, we can recognize clearly
the lumbal enlargement, the maximum extent being in the coccygeal
level.
2. The anterior column of the cervical enlargement is very welldeveloped in the transverse direction, but in the lumbal enlargement,
the anterior column is elongated rather in the ventro-dorsal direction.
These results are due perhaps to the lack of the lateral part of theanterior column in the lumbal enlargement, which innervates the musculature of the lower extremities.
3. In addition to the commonly deep coloured motor cells, there arelight coloured cells in the dorsal part and the lateral or medial peripheryof the anterior column. We guess that the latter might be associatedto the autonomic function.
4. Comparing the cell size of the anterior column between the Eubalaena
and man there is little difference in the cervical or the thoracic level ;but in the lumbal enlargement, the cells of the Eubalaena are doubtlessmuch larger than those of man. We are of the opinion that the sizeof the nerve cells is more related to the length of the nerve fibers
originating from them than to the body size of animals.
5. The posterior column is as a whole less developed ; only in C. 1
it is moderately large. The largeness in C. 1 is caused probably by thelower extension of the spinal root and its nucleus of the trigeminal
nerve, which are well developed in the medulla oblongata.
6. Fusion of the posterior columns of both sides is seen in the lower
thoracic and the coccygeal levels.
7. The Clarke's column is well developed especially in the lower
thoracic and the upper lumbal levels. Rostrally, the Clarke's column
is continued to the cervical nucleus of Stilling in the upper cervicallevels; also the caudal extension of the Clarke's column is clearly
developed.
8. The pars intermedia occupies a wide territory. The fibers of theanterior white commissure are crossed in the thoracic levels, making
small angles to the median plane.

OBSERVATIONS ON THE SPINAL CORD

243

9. The lateral horn cells exist in the levels from D. 1 to L. 8 in thelight coloured gray substance at the lateral border of the intermediatezone.
10. The reticular formation is relatively well developed in the levelsof C. 1 and 2, but far less in the other levels.
11. The central canal is fully obliterated for the whole length of the
spinal cord.
12. The spinal roots of the accessory nerve are very poorly developed,
and only in the lst cervical level.
13. The lower extension of the nucleus ambiguus is directly continuous to the lateral part of the anterior column in the lst cervical cord.
14. In the Eubalaena, cell groups corresponding to the lateral cervicalnucleus are recognized in the lst cervical level.
15. The pyramidal tract forms an unpaired bundle between the anterior funiculi of both sides in the lowest level of the medulla oblongata
and in C. 1. The pyramidal decussation is not demonstrated in spite ofcareful pursuit down to its lower disppearance.
16. At the dorsal margin of the lateral funiculus, an area possibly
corresponding to the dorsal spino-cerebellar tract is traceable.
ACKNOWLEDGEMENT

I am grateful to Prof. T. Ogawa for his constant direction and revision. My thanks are also due to Ass. Prof. H. Hosokawa and Mr. T.
Shida for their kind advices and offering of the unpublished data.
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DEXLER, H. & 0. EGER (1911). Beitriige zur Anatomie des Siiugerriickenmarkes. I Halicore
dugong Erxl. Morphol. Jahrb. 43, 107-207.
GANS, A. (1916). Die Pyramidenbahn der Phocaena. Anat. Anz. 49, 281-284.
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neural. Inst. a. d. Wien. Univ. IV, 286-312.
HATSCHECK, R. und H. SCHLESINGER (1902). Der Hirnstamm des Delphins. Arb. a. d.
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JELGERSMA, G. (1934). Das Gehirn der Wassersaugetiere. Leipzig.
KAPPERS, c. u. ARIENS, G. c. HUBER and E. c. CROSBY (1936). The comparative anatomyof the nervous system of vertebrates, including man. New York.
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244

Y. SEKI

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ABBREVIATIONS USED IN FIGS. 3-13.
ac,
af,
amf,
an,
ar,
awco,
eel,
ceCl,
cl,
cnSt,
cpm,
dlfL,
fr,
gco,
Id,

anterior column
anterior funiculus
anterior median fissure
arterial network in the subarachnoidal spaceanterior root fibers
anterior white commissure
lateral horn cells
caudal extension of Clarke's
columnlateral column
cervical nucleus of Stilling
postero-marginal cells
dorso-lateral fascicle of Lissauer
reticular formation
gray commissure
denticulate ligament

If,

nB,
ncl,
nppc,
pc,
pf,
pi,
pms,
pr,
py,
sgc,
sgd,
vcCl,
zsp,

*•.
06

lateral funiculus
nucleus of Bischofflateral cervical nucleus
nucleus proprius of the posterior
columnposterior column
posterior funiculus
pars intermedia
posterior median septum
posterior root fibers
pyramidal tract
Substantia gelatinosa centralis
Substantia gelatinosa dorsalis
Clarke's column
Zona spongiosa
deep coloured cells
light coloured cells

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r

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z
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246

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Y

pr

r
f
t
enS
c
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.
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g
i
F

gco
ac

h
t
. 5
.5
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OBSERVATIONSON THESPINALCORD

247

pr
pr

cpm

sgd
nppc

vcCI

c
a

l
m
。

. 6.
g
i
F

，
、

．，
an

pc

vcCI

l
e

l
e
e
ae

ae

一
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× 5)
ccord （
i
c
a
r
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ht
t
. 5
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Y.SEKI

248

pc

vcCI
e
e
l
veCI

ae
ae
amf

or

F
i
g
. 8.

pe
veCI
eel

ae

amf

−

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Y.SEKI

2
5
0

pms

pr
cpm

sgd
p
i

ceCI

awe

p1

。
c

a
c

amf

F
i
g
.1
2
. 1
s
tcoccygealcord （
× 5)

sgd

sgc

p
i

。。
WC

。
c

a
c

F
i
g
.1
3
.

OBSERVATIONSONTHESPINALCORD2
51

posteriorf
u
n
i
c
ul
u
s

union ofthe Goll's
n
u
c
l
e
iofbothsidescentral grayon the midlinesubstance

Burdochsnucleus

s
p
i
n
a
l rootand its
nucleus of the tri‑lower extension of

n
u
c
l
.n
. XI
I

geminalnerve

the nucleus ombi‑
g
υus

dor
s
al s
p
i
n
o
c
e
r
e
・
belar t
r
a
c
t(
pos‑

uppermost r
e
s
t of

山 l
y
)

t
heanteriorcolumn >:ーpyramidal tract fused intoaLemniscus medioliswedge‑shaped bundle
Fig. 1
4. Lower level of the medulla oblongata日br
ae arcuatae
internae
spinalroot and its
nucl
eus of the tri‑geminal nerve
radicesofn
.X
I
I
nuc
l
. amb1guus／

pyramids

bundle mediating betweennucl. olivaet
he pyramidsofbothsidesFig. 15. Upper level of th巴 medulla oblongata