AN ANATOMICAL STUDY ON THE LOWER EXTENSION
OF THE DORSAL VAGAL NUCLEUS TO THE
UPPER CERVICAL CORD IN THE
SPERM WHALE
YASUSHISEKI
Department of Anatomy, Nihon University School of Medicine, Tokyo

ABSTRACTThe lower portion of the dorsal vagal nucleus was examined anatomicallyin two specimens of sperm whale. At the level below the obex, the nucleus
seems to be divided into two cell groups, medial and lateral. The medialcell groups of both sides are fused with each other on the midline, which ischaracteristic in the sperm whale. The lateral cell group makes islands-likecell column along the long axis of the central nervous system. In some sections, these two cell groups are observed to be in complete continuity. Caudalwards, they can be traced up to the first cervical level, decreasing numberof cells and presenting beaded appearance. 'I'.hus, I could reconfirm that thelower extension of the dorsal vagal nucleus of the sperm whale belongs to thetype 3 in my previous classification.
INTRODUCTION

Although the lowest portion of the dorsal vagal nucleus is difficult to give a definite
description as to where to end and how, it usually is located approximately at thelevel of the pyramidal decussation. In certain other mammals the nucleus is reported to be further extended to the lower direction. But not much attention has
been paid on this latter fact.
Ogawa and Chen (1947) found that the lowest part of this nucleus was directlycontinued to the lateral horn nucleus of the upper cervical cord in the goat and deer,and similar finding was obtained in the sea lion by Mannen and Seki (1958). Seki(1966) had classified the form of the lowest portion of the dorsal vagal nucleus in fourtypes after 'comparative anatomical examination of such structures in many species ofmammals including primates, carnivores, ungulates, rodents and cetaceas.
In this report, it was able to reconfirm that the lower extension of the nucleus
belongs to the third type of the preceding classification, by a detailed observation in
two cases of the sperm whale.
MATERIALS AND METHODS

The materials were parts of those which had been collected by Dr. T. Kojima*,* Professor, Dept. of Anatomy, Nihon Univ. School of Med.
Sci. Rep. Whales Res. Inst.,
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SEKI

when he was on a whaling expedition in the Antarctic Ocean in 1949-50. Many
thanks are due to the profound kindness of Dr. Kojima to offer me the precious
materials to the present work.
The first specimen was the portion, 28 mm in length, covering from the level
3. 7 mm above the obex to the upper end of the spinal cord including the first cervicalcord. The second was the part, 44 mm in length, extending from the level 10 mmabove the obex to that part which included the first cervical cord. These two had
been preserved in formalin. Both materials, after having been cut off to meet thepurpose, they were refixed in Muller's solution in 37°C for two weeks and mounted incelloidin through the usual manner. Serial sections of 35 µ in thickness, along thetransverse plane for the first case and horizontal plane for the second, were made.
Each fifth sections (the first and sixth and so forth with the last order of each figure
being 1 and 6) were stained by the Kluver-Barrera method and each lOth sections(lOth, 20th, 30th, etc.) were also treated by the Weigert-Pal or Kultschitzky's
method for myelin staining.
RESULTS

The dorsal vagal nucleus and its lower extension are seen as palely stained areas in
the myelin stained sections and they are easily discriminated as a prominent cellgroup distinctly bordered from the surrdunding (Pl. I, Fig. 1). The examinationof the cell staining preparates reveals that substantially large cells, ellipsoidal orspindle-shaped, constitute the principal cellular component of the nucleus (Pl. I,Fig. 2). In transverse sections, majority of cells possesses long axis in the direction
oriented from the dorsomedial to ventrolateral, with approximately 50-100 µ in thelong diameter and 30-60 µ in the short one. They are large in size next to cells of
the hypoglossal nucleus in the lower medulla or the anterior horn of the upper spinal
cord of the sperm whale.
On the lateral or the dorsolateral to the nucleus is another aggregation ofsmall cells, part of which is found in a small number, though, within the above mentioned large cell group.
Fig. 1. Approximate distribution of cells in transverse sections of the lower medulla
and the lst cervical cord in case 1, Kluver-Barrera, X 12.
Each of drawings was made by accumulation of neighbouring 4 sections (stainedevery 5th sections) on one plane. Cells of dorsal vagal nucleus and its lower
extension were indicated by black dots.
a: Lower medulla above the obex (Section numbers; 281, 286, 291 and 296of block 2.). Note the hypoglossal nucleus lying far ventral apart from thebottom of the 4th ventricle.
b: Lowest medulla (Section numbers; 421, 426, 431and436 of block 1.). Dorsal
vagal nucleus is extended laterally and makes lateral cell group of lowerextension.
c: First cervical cord (Section numbers; 101, 106, 111 and 116 of block 1.).
Medial cell groups of lower extension of both sides are completely fused onthe midline.

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DORSAL VAGAL NUCLEUS

Fig. 1.

243

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SEKI

Other than these two different cell groups, there exist small collections of cells,
apparently similar in nature to those in the dorsal vagal nucleus, located in thereticular formation of the lower medulla and the lateral funiculus of the upper
cervical cord, distributed longitudinally with islands-like interruptions. But owing
to the limitation of the material obtained, no relationship of these cell groups withthe dorsal vagal nucleus or its lower extension could be clarified in this study.

~Fig. 1, a

Block 2-t-

Block 1

Fig. 1, b

Upper limit ofdorsal root---Plate Fig. 2-Fig. 1, c..... ·:.
Fig. 2. Approximate distribmion of cells projected from transverse sections (stainedevery Sth sections) on the horizontal plane in case 1, Kluver-Barrera, x4.5.
Arrows in left show levels of figures 1 and plate.

In the level higher than the obex, the dorsal vagal nucleus is situated close tothe fourth venticle and inside the ala cinerea as in the cases of most other mammals.
Conspicuously marked is the distance between this nucleus and the hypoglossal
nucleus because of the different location of the latter, which is observed to be inventral apart from the fourth ventricle in this level in the sperm whale (Fig. 1, a).
Sci. Rep. Whales Res. Inst.,
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DORSAL VAGAL NUCLEUS

Upper limit ofdorsal root!,.~f~:~.
Fig. 3. Approximate distribution of cells superimposed from horizontal sections on
the horizontal plane (dorsal view of the lower medulla and the lst cervical cord)in case 2, Kliiver-Barrera, X 4. *: Artificial cleft.
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SEKI

In the part lower than the obex, the dorsal vagal nuclei on both sides are recognized to approach gradually toward the midline, and a small number of cells areobserved to be existent sporadically between those two nuclei (Figs. 2 and 3). At
this level also, the ventrolateral ends of these nuclei, extend in places near the bundleof accessory nerve root running longitudinally at the dorsomedial edge of the lateralfuniculus, and tend to for a separate group at some distance of the main nucleus.
At the lowest medulla, these main nuclei completely fuse with each other, andform a transversely long cell group occupying a large area approximately in themiddle of the central gray substance (Figs. lb., 2 and 3). Beside this collection ofcells, there are found here and there discontinuous cell groups, islands-like in appearance, in proximity of the accessory nerve roots running longitudinally at the dorsomedial margin of the lateral funiculus (Fig. 1, b). In other words, the dorsal
vagal nucleus at this level can be distinguished in two parts; one is the main nucleus
formed by fusion of the left and right nuclei into a medial cell group, and the otheris the lateral one islands-like in appearance, and at the dorsomedial edge of the lateral funiculus. In certain other sections, these two groups of cells are observable
to be in complete continuity.
The medial cell group, as it goes lower, is decreased in number of cells in sections
from the lowest medulla to the upper cervical cord, until it presents a bead-likeappearance. This can be traced as far as the first cervical level, together with theislands-like lateral cell group (Fig. 1, c ). As has just been mentioned above, thematerials available did not have the part lower than the second cervical cord, so thatthe further extension could not be identified.
DISCUSSION

As to the ongm nuclei of glossopharyngeal, vagus and accessory nerves, twonuclei, ventral and dorsal, are distinguished. The former is situated at about thecenter of the reticular formation of the medulla oblongata, termed usually nucleus
ambiguus, and innervates the striated muscle. The latter is located at the dorsolateral or lateral to the hypoglossal nucleus, and has been thought to be the originof the preganglionic fiber of the autonomic nerve which innervates smooth muscles
and glands.
The dorsal vagal nucleus (or the dorsal motor nucleus of the vagus nerve) isclearly distiguished from its surrounding as a mass of middle sized nerve cells.
Some authors call this dorsal vagal nucleus including termination nucleus (termednucleus alae cinereae, on occasions) which is found immediately dorsolateral or lateral
to that nucleus. It would be relevant to divide it into two and discuss separately
instead of treating them as one entity: one as the termination nucleus consisting
principally of small cells, another as the origin nucleus which is a group of the middle
sized cells.
Olszewsky-Baxter (1954) and Mitchell and Warwick (1955) classified thesenuclear cells into three types, but their classifications are different from each other,and neither of these seem to be applied to the materials in this study.
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247

In the previous report (1966), I presented an idea to classify into four types thelowest structures of the dorsal vagal nucleus, after comparative anatomical investigations. In man, cat and rabbit, the lowest part of the nucleus decreases
gradually cells in number as it gows downward and disappears at as low the level ofthe pyramidal decussation (type 4 ). The pacific right whale and the common dolphin
also belong to this type. In the goat, the lower portion of this nucleus graduallyshifts its position to the lateral side, across the pyramidal decussation or the internalarcuate fibers, and reaches the dorsomedial edge of the lateral funiculus of the upper
cervical cord. This lower extention of the nucleus shows islands-like interruptions
along the long axis of the spinal cord and disappears in the first cervical cord in common cases (type 1). Similar findings can be obtained in the calf, sheep, horse,camel, sea lion, dog and bear. In the pig, unlike those of type 1, two lower extensions are observed, one on the medial side and the other on the lateral side. At
the lower medulla, the dorsal vagal nucleus is located at the dorsolateral to thecentral canal, and even in the portion lower than this level, extending cell groups
can be traced intermittently in the same position until to the second cervical level,
and in addition, as in case of type 1, laterally situated cell islands are still recognizable discontinuously along the dorsolateral edge of the lateral funiculus down to thesecond cervical cord (type 2). The medial cell group and lateral one are in directcontinuity with each other in some sections, but in others there are found occasionallya bundle of thin fibers running between the two groups connecting them. In thecase of the sperm whale, as in the pig, two lower extensions, medial and lateral, areidentified, but unlike the finding in the pig, the medial cell groups on both sides arefused in the level from the lower part than the obex to the upper cervical cord,
which is quite characteristic in the sperm whale (type 3).
Vermeulen (1915, 1916 and 1918) described that in llama, giraffe and porpoise,the dorsal vagal nucleus, at its lower end, constitutes the Nucl. commissuralis
motorius vagi, by the fusion of two nuclei at the dorsal part to the central canal.
The lateral cell groups of the lower extension in three types, 1, 2 and 3, are wellresemble the intermedio-lateral column (lateral horn nucleus) to develop into thethoracic cord, in respects of their position, size and massiveness of cells, and palely
stained gray substance. These features were also noted in Takahashi's report(1913) on the comparative anatomy of the lateral horn nucleus. However, I have
had no definitive evidence sofar that the dorsal vagal nucleus and the lateral horn
nucleus of the thoracic cord are actually connected even in a stepping-stone-pattern.
Similarly no reliable finding that the medial cell group is also connected with theintermedio-medial column at the farmer's lower part.
Of the lower extensions of the dorsal vagal nucleus, lateral cell group is positionally in a close relation with the accessory nerve root which runs longitudinallyalong the dorsomedial edge of the lateral funiculus, and it is imagined that these extensions send axons to this root. But the medial cell group did not give any special
finding on a possible fiber connection, except there were observed bundles of thinfibers which connects the lateral cell group and the medial one in some sections.
As for the function of the lower extensions of the dorsal vagal nucleus, noSci. Rep. Whales Res. Inst.,
No. 25, 1973.

248SEKI

explanation or suggestion could be offered derived from these anatomical findings
gained in this study. The utmost that can be deduced is the functions and the innervating areas to be inferred from those of the dorsal vagal nucleus, and no further.
CONCLUSION

A detailed anatomical examination was made on the dorsal vagal nucleus and its
lower extension in 2 cases of the sperm whale. At the lower part of the nucleus, thelower extension consists of the medial cell group and the lateral one at the portion
from the lower medulla to the first cervical cord. Characteristic is the fusion of themedial cell groups in both sides on the midline below the obex. In both cell groups
gradually decreased cells in number as they go down and continue sporadically inislands-like appearance. The existence of the lower extension was not identified
below the 2nd cervical cord.
Following the discussion on the structure of the lowest part of the dorsal vagal
nucleus in other mammals, I could reconfirm that the lower extension of the sperm
whale belongs to the type 3 in my previous classification.
REFERENCES
MANNEN, H. and Y. SEKI, 1958. Quelques resultats d'observation de la partie superieure de la moellecervicale anatomie comparee. Psychiat. et Neural. Japon. 60: 441-449.
MITCHELL, G. A. G. and R. WARWICK, 1955. The dorsal vagal nucleus. Acta Anat. 25: 371-395.
OGAWA, T. and Y. CHEN, 1947. On the direct continuance of the dorsal vagal nucleus and the lateral horn
nucleus of the spinal cord. Kaibogaku :(asshi (=Acta Anat. Nippon.), 23, 9. Proceedings of the 5lst
meeting of the Japanese Association of Anatomists (in Japanese).
OLSZEWSKI, J. and D. BAXTER, 1954. Cytoarchitecture of the human brain stem. Karger, Baser. 199 pp.
SEKI, Y., 1966. Comparative anatomical studies on the lower extension of the dorsal vagal nucleus to theupper cervical cord. Anat. Ree. 154: 421. Abstracts of 79th session of the American Association ofAnatomists.
TAKAHASHI, D., 1913. Zur vergleichenden Anatomie des Seitenhorns im Ruckenmark der Vertebraten. Arb.
Neural. Inst. Wien. Univ. 20: 62-83.
VERMEULEN, H. A. 1915, 1916 and 1918. Cited from KAPPERs, C. U. A., G. C. HUBER and E. C. CROSBY,1936. The Comparative anatomy of the nervous system of vertebrates, including man. Vol. 1. Macmillan,
N. Y. 864 pp.

Sci. Rep. Whales Res. Inst.,
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DORSAL VAGAL NUCLEUS

EXPLANATION OF PLATE I
Fig. 1.

Lower medulla below the obex (Section number 130 of block 2, Case 1), Kultschitzky,

Fig. 2.

First cervical cord (Section number 261 of block I, Case 1), Kluver-Barrera, x40.
-> <- : Midline.

x6.

Abbreviations Ill Text-figureand Plate.

CA

Anterior horn

NANucleus ambiguus

CPFLM

Posterior horn

NDV

Dorsal vagal nucleus

Medial longitudinal fascicle

NFP

Nuclei of posterior funiculi

FSSolitary fascicle

NNXII

Hypoglossal nucleus

Lateral cell group of theNTDVLCG
MCG

Nucleus of descending tractof the trigeminal nerve

lower extension
Medial cell group of theRNXIAccessory nerve root

lower extension

VQ

Fourth ventricle

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

249

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