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| [[File:Mark_Hill.jpg|90px|left]] This historic 1943 paper by Pearson described development of the spinal accessory nerve.
 
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{{Ref-Pearson1939}}
{{Ref-Pearson1941a}}
{{Ref-Pearson1941b}}
{{Ref-Pearson1943}}
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[https://www.ncbi.nlm.nih.gov/pubmed/?term=spinal+accessory+nerve+development Search PubMed spinal accessory nerve development]
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=The Spinal Accessory Nerve In Human Embryos=
 
ANTHONY A. PEARSON
 
 
Hull Laboratory of Anatomy, The University of Chicago‘
 
NINETEEN FIGURES
 
(Accepted for publication September 1, 1937)
 
 
INTRODUCTION
 
This paper is one of a series of studies on the development
and analysis of the components of the cranial nerves in human
embryos undertaken at the suggestion of Prof. C. Judson
Herrick. The study is based on serial sections of embryos cut
in several planes and stained by various methods. This Work
was facilitated by Prof. G. VV. Bartelmez, Who placed at my
disposal several series of human embryos stained With acid
carmine and reduced silver, and a number of unstained specimens, and by Dr. Edith Potter of Lying-In Hospital who also
contributed several embryos.
 
 
The author wishes to thank Dr. G. L. Streeter of the Carnegie Institution of Washington at Baltimore for the privilege
of studying a large number of hematoxylin series of human embryos, and Profs. Davenport Hooker and Ira Hogg of the
department of anatomy of the University of Pittsburgh for
the use of a number of significant series of toluidin blue and
pyridine silver preparations during a short visit to their
laboratories. This material has been supplemented with pyridine silver preparations and a number of series stained with
activated copper protargol (Bodian, ’36) made by the author.
 
* This research was aided by a grant to The University of Chicago by the Rockefeller Foundation. Study of the material at the department of anatomy of the University of Pittsburgh was aided by a grant from the Penrose Fund of the
American Philosophical Society.
 
 
 
 
It was found that for the study of fiber bundles within the
brain, the pyridine silver gave the best results, but the peripheral nervous system was far superior when stained with the
activated protargol or a modified Rogers in which protargol
was used (Bartelmez and Hoerr, ’33) and copper added to the
protargol as in the former stain. After experimenting with
a large number of pig embryos it was found that a mixture
of formol (5%), acetic acid (5%), and alcohol (80%) gave
the best fixation with the least amount of shrinkage; fixation
and shrinkage are factors of vital importance. The results of
the staining with the protargol depend largely on the fixation.
In embryos, where the tissues contain so large amount of
Water and particularly in the very loose tissues around the
central nervous system from which the leptomeninges develop,
shrinkage often has a marked effect. This very delicate tissue
around the brain and spinal cord must be preserved intact
with as little shrinkage as possible in order that one may
follow the course of the smallest nerve rootlets. To obtain a
more thorough embedding the fluids and embryos were aspirated under a vacuum pump to remove all possible air
bubbles. The specimens were embedded in methyl-benzoate
celloidin before being infiltrated with paraffin, and the best
results were obtained when the vacuum pump was again used
while the specimen was in the last change of hot parafiin.
Many embryos stained with the best of available methods
must be studied intensively before an approximation of the
whole story of any one nerve can be learned. This is particularly true of the spinal accessory nerve which is subject to
many va_riations.
 
 
The author has felt that there is too wide a gap between the
approach to the nervous system in gross anatomy and in
neurology. It is my opinion that preparations of embryos,
old enough for the nervous system to be well formed and in
which the complete course of peripheral nerves can be followed from cell of origin to termination in much the same way
that Herrick and others worked on functional systems in fishes,
would contribute to an understanding of the nervous system
as a whole.
 
Since the literature on the XI cranial nerve is summarized
in the recent book by Ariéns Kappers, Huber and Crosby
(’36), only such references as are pertinent to this discussion
will be mentioned. According to current nomenclature, XI
has two parts: a spinal portion, nervus accessorius spinalis,
and a cranial portion, nervus accessorius bulbaris. The distribution of the latter is generally included with the vagus.
The spinal part is usually considered as purely motor, special
visceral efferent; however, its classification is still debated.
This account is concerned primarily with the spinal portion
of this nerve.
 
The human embryos referred to specifically in the following
 
description are listed below with the necessary data concerning each:
 
KUMAN EMBBYO No. CROWN-RUHP LENGTH PROBABLE AGE METHOD 0]‘
 
IN HILLIMETIBS IN WEEKS PREPARATION
 
1223 Activated protargol
1331 Pyridine silver
 
11 Activated protargol
 
19 Pyridine silver
1498 Pyridine silver
 
15 Activated protargol
1433B Pyridine silver
 
 
Human embryos nos. 11 and 15 are in the author ’s collection, no. 19 belongs to
the collection at the department of anatomy of the University of Pittsburgh, and
the others listed are in the embryological collection at the department of anatomy
of The University of Chicago.
 
 
LIST OF ABBREVIATIONS
 
A.bas., arteria basilaris
 
A.vert., arteria vertebralis
 
bulb.acc.r.gang., bulbar accessory root
ganglia
 
eo., communicating filament between the
trunk of spinal XI and the rudimentary ganglion of C 1
 
dens cpis., dens epistrophei
 
f, spinal accessory root fibers
 
fas.sol., fasciculus solitarius
 
for., intervertebral foramen between the
first and second cervical vertebrae
 
forarnen trans., for-amen transversarium
 
fun.post., funiculus posterior
 
gang., ganglion
 
gang.C1, ganglion of the first cervical
nerve
 
gang.C2, ganglion of the second cervical nerve
 
gang.jug., ganglion jugulare
 
gang.N.V, ganglion semilunare
 
gang.nod., ganglion nodosum
 
gang.R.acc.sp., spinal accessory root
ganglion
 
gang.sup., ganglion superius
 
11, highest filament of the dorsal root
of the first cervical nerve
 
h.r.sp.acc., highest root of the spinal
accessory nerve
 
lig.trans.atl., ligamentum transversum
atlantis
 
M.scm., musculus sternocleidomastoideus
 
M.trap., musculus trapezius
 
I\T.VII, nervus facialis
 
N.VIII, nervus acusticus
 
N.IX, nervus glossopharyngeus
 
N.X, nervus vagus
 
N.X et gang., nervus vagus et ganglion
jugulare
 
N.XT, nervus accessorius
 
N.XI* (fig. 18), on the right, indicates
the region where XI descends with
X; on the left side, a lower point on
XI on the opposite side
 
N.XII, nervus hypoglossus
 
n.a., nucleus originis nervi accessorii
spinalis
 
N .acc.sp., nervus accessorius spinalis
 
N .acc.sp. et gang., spinal accessory nerve
and spinal accessory root ganglion
 
os oce., os occipitale
 
os temp., os temporale
 
R.ant.C1, anterior root of the first cervical nerve
 
R.ant.C2, anterior root of the second
cervical nerve
 
R.ant.C3, anterior root of the third cer~
vical nerve
 
R.ant.C4, anterior root of the fourth
cervical nerve
 
R.ant.C5, anterior root of the fifth cervical nerve
 
R.N.acc.sp., root of the spinal accessory
nerve
 
R.post.C1, posterior root of the first
cervical nerve
 
R.post.C2, posterior root of the second
cervical nerve
 
R.post.C3, posterior root of the third
cervical nerve
 
B.post.C-1, posterior root of the fourth
cervical nerve
 
R.post.C5, posterior root of the fifth
cervical nerve
 
Rr.N.XII, roots of nervus hypoglossus
 
Rr.N.acc.bulb., roots of nervus accessorius bulbaris
 
Rr.N.acc.sp., roots of spinal accessory
nerve
 
s.tr., sinus transversus
 
t.sp.XI, trunk of spinal XI
 
X, cross-cut spinal accessory root fibers
 
 
NUCLEUS OF ORIGIN
 
The nucleus of origin of the spinal accessory nerve is well
shown in several series, but particularly well in no. 19. It is
easily recognized by its constituent large multipolar cells with
their large eccentric nuclei, scanty cytoplasm and prominent
nucleoli (fig. 1). The small granules of chromatin of the
nuclei stand out in sharp contrast with the large nucleoli. It
is thought that in certain of the stages studied, the dense
neuropil around the cells at certain levels is responsible for
making this cell column stand out more distinctly (fig. 2).
The cells of this nucleus are somatic in type, in agreement.
 
 
Fig. 1 Cells from the spinal accessory cell column in the upper cervical cord
of a human embryo (no. 1433B). Camera lucida drawing. Pyridine silver preparation. X 750,
 
with Black (’13) who identified the origin of spinal X1 in the
upper two or three cervical segments of the spinal cord of a
newborn babe.
 
This nucleus is located in the lateral part of the ventral
horn of the cervical cord. The cells of this nucleus form a
column which extends from about the junction of the spinal
cord with the medulla obloiigata caudally into the sixth cervical segment of the cord. The nucleus is larger at certain
levels, smaller at others, and for a few sections at a time may
drop out completely. The type of material on which this description is based is illustrated in figure 2, and the distribution
of the cells and the position of the nucleus in the ventral 110m
in figures 3 to 7.
 
 
In the first cervical segment the nucleus is seen in cross
sections as a group of about twelve to sixteen cells (fig. 3) in
the ventral l1orn, lateral to the medial cell columns. The
 
Fig. 2 A photomicrograph of the accessory nucleus at the lzecond cervical level
of :1. human embryo (no. .19). .l’_vridine silver preparation. X 320.
 
accessory nucleus becomes somewhat larger and more prominent in the lower and middle portions of the. first cervical
segment, but as one traces these cells to the. upper limit of the
spinal cord the nucleus becomes smaller, and disappears at
about tl1e level of the highest ventral rootlets of the first cervical nerve. In older embryos, where the lowermost decussating fibers of the pyramids may be taken as the lower boundary of
the medulla oblongata, one might consider that the spinal
accessory nucleus extends for a short distance into the medulla
oblongata (Black, ’13). In the material studied it does not
appear to be directly continuous with any cell group or column within the brain stem, which is also the case in the newborn
babe (Black, ’13). It is not continuous with or in line with
the hypoglossal nucleus, as has been described in certain lower
animals (Addens, ’33, p. 343; and Beccari, ’22).
 
 
 
Figs.3 to 7 These are drawings of representative cross sections of successive
levels of the spinal cord, C1 through C5, of a human embryo (no. 19), illustrating
the extent of the accessory nucleus and its position in the ventral horn. The
right and left sides of figures 3 and 4 are from adjacent sections. Pyridine silver
preparations. X 40.
 
 
 
In the second cervical segment (fig. 4) this nucleus has much
the same relations as in the preceding. The cells of the ventral horn are more densely packed and appear to have crowded
the accessory nucleus slightly laterad. It is in the upper
cervical segments of the cord that the nerve bundles which
form the spinal accessory nerve can be demonstrated most
clearly as they leave the nucleus of origin.
 
 
In the third cervical segment (fig. 5) the ventral horn has
enlarged somewhat, a ventrolateral group having come into
the picture, while the accessory nucleus now takes a slightly
more dorsolateral position.
 
 
From here caudad, this nucleus is less prominent than in
the higher cervical levels. In cervical segments four and five
(figs. 6 and 7) the ventral horn shows further enlargement in
that dorsolateral cell columns occupy a position dorsal to the
accessory nucleus. Although practically surrounded by other
cell columns, the nucleus retains its individuality by definite
morphological characteristics which distinguish it from the
other cell groups.
 
Throughout the extent of this nucleus its position is much
the same. The changes in cell grouping about it alter the
picture of the ventral horn, but this cell column is almost a
straight line, extending into the upper part of the sixth cervical segment. Here the relations are much the same as in the
fifth segment, but the cells become fewer and soon drop out
completely.
 
COURSE or SPINAL XI
 
The fibers arising from the accessory nucleus pass dorsad
in loose formation and converge into small bundles. These
may pass almost directly dorsad and laterad to the surface of
the cord, they may gradually ascend cephalad as they pass
dorsad and laterad, or they may pass directly dorsad and
then ascend for a certain distance before making their exit from the cord. The bundles which make their exit nearer the
ventral funiculus pass more directly toward the lateral surface of the cord thus having a shorter internal course. The
rootlets emerging nearer the dorsal funiculus usually pass
farther dorsally in a more medial position, ascending in small
bundles for a varying distance before turning out. The spinal
accessory roots are larger and more numerous in the higher
cervical levels than in the lower levels. In fact, on tracing
the roots from above down, they become progressively smaller
and less numerous until they drop out completely in the fifth
or sixth cervical segment of the cord, as would be expected
from the distribution of the cells of origin. The fibers arising
in the lower part of the accessory cell column tend to ascend
farther within the spinal cord than many of the bundles aris—
ing higher. However, there are fiber bundles that turn out
in the lower levels near their cell of origin. The roots of
spinal XI do not emerge in a straight line but in a very ir—
regular manner, some being much nearer the dorsal funiculus.
Often in one section two roots can be seen leaving from the
lateral surface of the cord, one being much more dorsal than
the other (fig. 3).
 
On emerging from the cord the rootlets of spinal XI turn
cephalad close under the dorsal roots of the cervical nerves.
With the addition of higher rootlets, the trunk of XI grows
larger as it courses cephalad. This trunk lies close to the
dorsal roots where usually there is no intermingling of fiber
components. However, the relations of the trunk of spinal
XI to the first cervical dorsal root and ganglion are found to
be variable (Streeter, ’04, and others). The dorsal root and
ganglion of the first cervical segment may be well formed, or
they may be either greatly reduced in size or apparently lacking. Spinal XI may have no connection with either the dorsal
root or ganglion of C1, or it may be in intimate relation with
either or both. Weigner (’01) in adults, Streeter (’04) in
human embryos, Windle (’31) in cats and monkeys, and others
have described such anastomoses. My observations on the
whole agree with the findings of these investigators. Additional findings in the embryos at my disposal will be briefly
outlined.
 
 
In human embryo no. 11 the rootlets forming spinal XI can
be traced as they ascend close under the dorsal roots of the
upper cervical nerves. Passing in close company with the
trunk of XI is an anastomotie branch, with clusters of ganglion cells along it, which passes between the dorsal roots of
C1 and C2. The trunk of XI together with the rootlets of XI
arising from the first cervical segment merge with the dorsal
root of that level as it passes into its ganglion (figs. 8 and 9, left). The dorsal root ganglion of C1 on one side is partially
divided into two parts (fig. 9) which are separated by a constriction in the ganglion. The medial part, which receives XI,
lies within the embryonic meninges and is situated slightly
cephalad to the more lateral part outside the dura, which last
at this time is in the process of differentiation. In this embryo it was not possible to trace the individual fascicles of
XI through the ganglion, as its fibers are lost among the ganglion cells. Just above the ganglion of C1 the fibers of XI collect into a compact bundle (fig. 8, left), which bundle constitutes the trunk of XI and passes cephalad to enter the
foramen magnum.
 
 
 
Fig. 8 This is a composite semidiagrammatic drawing, illustrating on the left
the relation of the higher spinal accessory roots and the first cervical nerve, and
the trunk of XI a it arches cephalad and ventrad through the bulbar accessory
root ganglia to join X. On the right, an accessory root ganglion is indicated at
the approximate point below which the trunk of XI ascends from the ganglion of
C1. See figures 9, 13 and 14. Human embryo no. 11. Approximately X 12.
 
 
 
In embryo no. 1223 the spinal XI trunk ascends close under
the dorsal root of the second cervical nerve. The relation of
the two bundles is intimate and it is diflicult to determine
whether there is an exchange of fibers. Above this XI immediately runs into and through a small ganglion (fig. 10)
which is located approximately between the planes of exit of
the first and second cervical nerves from the vertebral canal.
At the lower end of this ganglion a small bundle of fibers is
given oil’ which runs ventrad to the ganglion of the second
cervical nerve. At the upper end of the ganglion another
small bundle of fibers can be traced ventrad and slightly
cephalad to the small rudimentary ganglion of the first cervical nerve (fig. 11, left). There are apparently no dorsal roots
from the first cervical segment of the spinal cord. The relations are similar on both sides of this embryo.
 
 
In one embryo (no. 15) on one side a dorsal root bundle at
the level of the second cervical segment turns cephalad with
the trunk of XI, instead of passing to the dorsal root ganglion at that level. These fibers ascend with XI, the two components forming a fairly compact bundle. Just before reaching the level of exit of the first cervical nerve, this bundle
runs into a small ganglion which lies within the dura jllst
dorsal to the dentate ligament and slightly below the exit of
the first cervical nerve from the vertebral canal. As the fibers
pass into and through the ganglion, the fibers of XI tend to
gather into small bundles on the medial side of this ganglion
(fig. 12, right). At the upper end of the ganglion, XI separates from the dorsal root fibers which pass laterad to join
the ventral root of first cervical nerve. As far as I could
discover there are no dorsal root fibers from the first cervical
segment of the cord on this side. In the same embryo but on
the opposite side, XI adheres closely to the ganglion of C1.
The ganglion on this side is small and in much the same position as on the opposite, only it is at the level of the exit of the first cervical nerve. Here there is a small dorsal rootlet
of C1.
 
In embryo no. 1498 the ganglion of C1 is separated into two
parts: a medial ganglion within the vertebral canal close to
the vertebral artery, and a lateral ganglion outside the dura,
just above the neural arch of the first cervical vertebra. The
trunk of spinal XI passes through the medial ganglion. In
this series of preparations the dorsal rootlets of C1 are small
and difficult to follow. The highest of these rootlets appear
to join the XI trunk above the medial ganglion, which is the
case in several other embryos. As the trunk of XI passes
through the ganglion, fibers from the trunk can be seen running among the ganglion cells at both the upper and lower
ends of the ganglion. It was not possible to determine definitely whether these were dorsal root fibers ascending with
XI, but this is very likely the case. In the lateral side of the
medial ganglion, fibers collect to pass to the lateral part of
the ganglion of C1, located outside the dura.
 
After examining the course of the spinal accessory nerve in
a large number of embryos, one is struck by the variations
that occur. But neglecting the many details of numerous
specimens, a few general statements can be made as to the
usual course of the nerve. The trunk of spinal XI ascends
between the dorsal and ventral roots of the upper cervical
nerves. The trunk lies close under the dorsal roots, where
it usually keeps its integrity up to the level of the first cervical segment. Occasionally it is in intimate relation with the
 
Fig. 9 This is a cross section of the first cervical segment of the spinal cord.
Note on the left the accessory root joining the dorsal root of C1 at the medial
end of the ganglion of C1, and on the right the position of the accessory trunk
just above the level of the ganglion of 01. Human embryo no. 11. Activated
protargol preparation. X 23.
 
Fig. 10 Cross section of the vertebral canal just above the level of the dorsal
root and ganglion of C2. In this embryo there is a small ganglion on the trunk
of XI at this level. Human embryo no. 1223. Activated protargol preparation.
X 23.
 
Fig. 11 The level of this figure is a little above that of the preceding one.
On the left a small communicating filament is indicated which passes between the
very small ganglion of Cl and the trunk of XI. Human embryo no. 12:23. Activated protargol preparation. X 23.
N. qcc sp. eh qanq.
 
 
dorsal root of the second cervical nerve. It is in relation with
the first cervical nerve where the variability more often
occurs. This is probably largely due to the variability of the
dorsal root ganglion of the first cervical nerve. Usually the
trunk of XI passes through the ganglion of C1, often joining
 
   
 
 
Fig. 12 A cross section through the upper cervical cord of a human embryo
(no. 15). The right side of the field is just below the level of exit of the first
cervical nerve. Note the ganglion within the dura and the absence of a dorsal
root. The left side is at the level of the ganglion of the first cervical nerve and
shows the more usual relation of XI and C1. Activated protargol preparation.
X 23.
 
the ganglion at its junction with its dorsal root. Sometimes
the ganglion of C1 is divided into medial and lateral halves,
in which case XI may pass through the medial half. Again
XI may pass in intimate relation with the dorsal root of C1
and avoid that ganglion, or it may avoid both dorsal root and
ganglion of 01. In addition to its relation to the ganglion of 01, there are often ganglionic masses on XI before it reaches
the level of the ganglion of C1.
 
 
Streeter (’04) found that the ganglionic crest of the hindbrain was continuous with that of the spinal cord. Arising
from part of this crest is a series of ganglia which extends along XI to the cervical ganglion series. He referred to these
as accessory root ganglia and pointed out that they are not
to be confused with the precervical ganglion of Froriep.
Froriep’s ganglion represents an extra spinal ganglion and,
when present, is in relation to the hypoglossal nerve. Streeter considered that the ganglia which often occur on XI between
the upper cervical nerves are developed from the spinal crest.
It is suggested that the ganglia along the portion of XI that
receives bulbar rootlets should be referred to as bulbar accessory root ganglia and those ganglia situated on the spinal
 
 
 
Fig. 13 A cross section taken a little above the level of figure 9. The left
side of the figure shows the ganglionic Mass which is sometimes present on the
trunk of XI just above the ganglion of 01. Lower down in the field one will see
IX, X and X1 in the relation in which they descend through the jugular foramen.
The right side is a little above the level of the left and passes through the bulbar
accessory root ganglion and the jugular ganglion. Human embryo no. 11. Activated protargol preparation. X 17.5. '
 
 
Fig.1-1 A drawing similar to figure 13, but at 21 slightly higher plane. On
the left note XI arching ventrad to join X. The right field is just above the
arch of XI, and bulbar accessory root bundles are present. Human embryo no. 11.
Activated protargol preparation. X 17.5.
 
portion of this nerve below the bulbar rootlets, as spinal
accessory root ganglia (figs. 10 and 11).
 
Along XI, where it passes ccphalad and ventrad in a broad
curve to join X, is the series of bulbar accessory root ganglia (figs. 8, 13, 14 and 19). These ganglia form more or less of
a sheath around the trunk of XI, which sometimes continues
into the cervical region. In a few cases it fuses with the dorsal root ganglion of C1. Ventrally this series is continuous
with the jugular ganglion of X (fig. 18), while dorsally it usually becomes smaller and extends for a variable distance along
XI. This series of ganglia is located on the portion of the
nerve within the cranial cavity, above the point where the
nerve turns sharply ventrad toward X after passing through
the foramen magnum. Below the level of the bulbar rootlets
and at about the level of the highest dorsal rootlets of 01,
there is often found a small ganglionic swelling on XI (figs.
8 and 13). This ganglion is variable in size, sometimes lacking, but is usually found separated from the bulbar root
ganglia. In some embryos a separation is indicated only by
a constriction, or the ganglion is seen as the continuation of
the bulbar accessory root ganglia. Just below this ganglion,
XI passes into relation to the dorsal root of C1. In certain
embryos there are scattered small ganglia on anastomotic
branches between the dorsal roots of the upper cervical
nerves, which sometimes are in relation with XI, and often on
the trunk of XI itself. In one embryo (no. 1223) where the
dorsal root and ganglion of C1 were greatly reduced in size
there is a small but well—formed ganglion on XI between the
levels of the dorsal root ganglion of C1 and C2 (see p. 253 and
fig. 10). In certain embryos the dorsal root ganglion of C1
is apparently shared with spinal XI.
 
 
The presence of ganglion cells along the course of XI has
suggested to various investigators that this may be a mixed
nerve, having a sensory as well as a motor component.
Streeter thought that XI being laid down earlier may guide
dorsal root fibers out of the expected path and along its own.
This appears to be the case in certain embryos. It remains
to be determined whether these ganglia along XI usually persist in the human adult and whether XI has a component with
cells of origin either in the ganglia mentioned or the ganglion
of C1, or both. Windle (’31) found that after section of the peripheral end of XI in the cat, chromatolyzed cells were
found on the trunk of XI and a significant number in the
ganglion of the first cervical nerve. Windle and De Lozier
(’32) suggested that the sensory component of XI is likely
 
 
 
Fig. 17 A sagittal section through the jugular foramen of a human embryo
(no. 1498), illustrating the relation of the vagus and accessory nerves. Pyridine
silver preparation. Approximately X 50.
 
concerned with proprioception. On the basis of Marchi preparations, Hinsey and Corbin (’34) concluded that in the cat,
XI contains no proprioceptive fibers with cells of origin in
 
Fig. 15 Cross section of the flrst cervical level of the spinal cord of a human
embryo (no. 1331). Note the caudal end of the fasciculus solitarius, which extends into the upper cervical region, and the accessory root fibers which run dorsad.
The trunk of spinal XI is shown in the left first cervical ganglion. The right
and left sides of this figure are from adjacent sections. Pyridine silver preparation. X 59.
 
Fig. 16 This drawing is similar to figure 15. It is a. crosssection through the
upper part of the third cervical level of a human embryo (no. 19), showing accessory root fibers turning up toward the posterior funiculus. Pyridine silver preparation. X 59.
 
 
 
 
Fig. 18 This is a composite semischematic drawing showing the origin and
course of the spinal accessory nerve in a human embryo (no. 19). The cord is
drawn to represent two levels, the left side being lower than the right. On the
left, the accessory root fibers are shown ariing from their nucleus of origin and
passing out of the cord to join the trunk of the spinal accessory nerve at the
second cervical level. A small accessory filament is drawn turning up toward the
posterior funiculus. The upper right half of the figure is through the first cervical level of the spinal cord, and, in addition to the nucleus of origin, shows variations of the intraspinal course of the accessory root fibers. The accessory root
fibers, the dorsal root of the first cervical nerve and the spinal accessory trunk
converge at the medial end of the dorsal root ganglion of that level. The trunk
of spinal XI continues cephalad and, as it arches forward passing through the
bulbar accessory root ganglion, it is joined by the bulbar accessory root fibers
(not shown). On reaching the jugular ganglion, XI descends in close company
with the vagus. A XI descends it gradually moves from a dorsal to a lateral
position with respect to the vagus. On the left side of the figure the external
branch of XI is shown leaving X and passing to the sternocleidomastoid and
trapezius muscles. From pyridine silver preparations. Approximately X 28.
 
the first four cervical dorsal root ganglia. Strecter (’04) has
shown that in the development of the vago-accessory complex,
the cephalic end becomes predominantly sensory, and the
caudal end predominantly motor.
 
It is interesting to point out that in one embryo (no. 1331),
at the level of the first cervical segment where the fibers of XI
are well impregnated, small fascicles of accessory fibers can
be recognized other than those arising from the ventral horn
cells (fig. 15). These fibers can be traced out of the accessory
 
 
Fig. 19 A reconstruction of the peripheral nerves in a. 6-week human embryo,
17.5 mm. long. His collection embryo FM. Slightly modified from figure 12,
Streeter (’04). X 11.
 
rootlets dorsad toward the posterior funiculus and into the
region of the caudal end of the fasciculus solitarius, which as
it descends takes a. position nearer and nearer the posterior
funiculus. As Windle (’31) observed in the cat embryo, these
fibers appear to turn caudad with that fasciculus. In our no.
1331, prepared by Cajal’s method, the fibers of the fasciculus
solitarius could be followed distinctly into the upper cervical
cord. In this embryo the trunk of XI passes through the
center of the dorsal root ganglion of 01. In other embryos,
Where XI runs through the ganglion of C1 and there are
spinal accessory root ganglia, occasional fibers can be seen
turning dorsad toward the posterior funiculus (fig. 16). Some
of these occur also in the second and third cervical segments.
This strongly suggests that at least during development there
is in certain embryos a small sensory component in spinal X1.
 
As the spinal accessory trunk turns ventrad toward the
vagus (figs. 8, 14, 18 and 19) it passes through or under the
bulbar accessory root ganglia and is joined by the bulbar
accessory root fibers. Together they descend through the
jugular foramen close against the dorsal side of the jugular
ganglion and the vagus nerve (fig. 13, left). Here fibers of
X and XI are medial to the jugular vein and are in close
relation (fig. 17), making it difficult to determine in this material what components constitute the external branch of XI
(fig. 18) which separates from X at the lower end of the
foramen. DuBois and Foley (’36) have shown through degeneration experiments in cats that spinal XI can be traced
into the external branch of the accessory, and bulbar XI into
the recurrent laryngeal nerve, indicating a definite peripheral
distribution.
 
As XI descends it gradually creeps around X to a lateral
position and then leaves X to pass laterad to the sternocleidomastoid and trapezius muscles. The whole course of spinal
XI, from origin to termination, is shown schematically in
 
figure 18.
 
 
DISCUSSION
 
It is thought that spinal XI is in reality a spinal nerve
which is joined by bulbar XI within the cranial cavity, the two
parts fusing as they join the vagus. These form a complex
which has been difficult to analyze.
 
While the main component within spinal XI is motor, there
is strong evidence that in certain embryos there may be sensory fibers. Windle and De Lozier (’32) have shown evidence
in cats that these fibers do not carry painful stimuli but more
likely proprioception. The cells of origin of this sensory element are thought to be located either 1) within the ganglia
which often occur along the trunk of XI, or 2) in the ganglion
of C1 in relation to which spinal XI usually passes, or 3) in
SPINAL ACCESSORY xanvn 265
 
both. These sensory fibers may enter the cord with the roots
of spinal XI where they then separate from the motor fibers
and turn dorsad toward the posterior funiculus, or they may
enter with the dorsal root fibers of C1. The majority probably take the latter course.
 
The nucleus of the spinal accessory in the stages studied
appears to be an integral part of the ventral l1orn. Any conclusions drawn from the position of the nucleus should be
made cautiously until the earlier embryology of this cell column is more thoroughly understood.
 
'I‘he question as to whether this nerve is visceral or somatic
is still debated. This question would seem to resolve itself
into the problem as to whether there are elements of branchio—
meric origin within the sternocleidomastoid and trapezius muscles, or whether these muscles are entirely of somatic origin.
Again the answer will have to come from studies of younger
embryos. Phylogenetic evidence is of interest but 11ot conclusive with regard to this problem. This question has been
recently reviewed by Addens (’33) who regarded spinal XI
as a somatic efferent nerve, and Straus and Howell (’36) who
thought this nerve to be of visceral origin. The position of
the cells of origin within the ventral horn would cause one to
favor the former view, while the manner in which the accessory roots leave the spinal cord, i.e., between the dorsal and
ventral roots, would support the latter. Sufiicient evidence to
rule out the one and substantiate the other is still lacking.
 
SUMMARY
 
1. The cells of origin of the spinal portion of the accessory
nerve are somatic in type and form a cell column which is an
integral part of the ventral horn. The accessory cell column
extends from the region of the junction of the spinal cord
with the medulla oblongata into the sixth cervical segment.
 
‘.2. The intraspinal course of the accessory rootlets is varia.hle. Some rootlets emerge at the level of origin, others ascend
for certain distances within the spinal cord before turning out.
The line of emerging accessory roots from the spinal cord is
not regular, certain roots being more dorsal than others.
 
3. The course of the spinal accessor_v trunk within the vertebral canal and its relation to the dorsal root and ganglion of
the first cervical nerve are variable. Usually the trunk of
spinal XI passes through the ganglion of C1. Variations
which occur in the material studied are discussed in the text.
 
4. The presence of ganglia along the trunk of spinal XI
and the relation of the trunk to the ganglion of 01 suggest
the presence of a sensory component. The occasional accessory root fibers which turn up toward the posterior funiculus
strengthen this view.
 
Literature Cited
 
.\noi:Ns, J. L. 1933 The motor nuclei and roots of the cranial and first spinal
nerves of vertebrates. Zeitschr. f. Anat. 11. Entxvit-kl., I. Abteil. <1.
Zeitsehr. f. ges. anat., Bd. 101, S. 307-410.
 
Amiiss KAPP1-IRS, C. L'., G. C. 111:3:-:11 AND E. C. CROSBY 1936 The comparative
anatomy of the nervous system of vertebrates including man. The
Macxnillan (‘.o., New York.
 
B,ucT1-:1.Mr:z, (1. W., AND N. L. liomxn 1933 The vestibular elul) endings in
Ameinrns. J. Comp. Ncu1'., vol. 57, pp. 401-428.
 
BI-‘.(‘(‘AK1, N. 1922 Studi comparativi sulla struttura del Rliombene.et'alo. Arch.
ital. di anat. e. (11 en1l)riol., vol. 19, pp, 1223-292.
 
Bi..~at‘x, D. 1). 1913 On the so-called ‘bulbar’ portion of the accessory nerve.
Abstract. Anat, Rce., vol. 8, pp. 110-112.
 
l}()I)IAN', I). .1936 A new method for staining nerve. fibers and nerve endings in
mounted paraffin sections. !Anat. Rec., vol. 65, pp. 89-97.
 
D1'Bo1s, F. 8., AND J. O. FOLEY 1936 Experimental studies on the vagus and
the spinal accessory nerves in the cat. Anat. Ree., vol. (54, pp. 285-307.
 
}<‘RORIi~;1-, A. 1882 llher ein Ganglion des llypog-lossns und Wirhelanlagen in der
Occipitalregion. Arch. f. Anat. u. Physiol. Anat. Abt., S. ‘.279-302.
 
1li.\'sr.v, J. (.‘., A.\'D K. B. (‘oasis 19:14 Observations on the peripheral course
of the. s(‘11sor_v fibers in the first four cervical nerves of the eat. J.
Comp. Ncnr., vol. 60, pp. 37-44.
 
S'rx.—\Us, W. L., JR., AND A. Bimzim HOWELL 1936 The spinal accessory nerve
and its musculature, Quart. Rev. Biol., vol. 11, pp. 387-405.
 
S1'R.m-‘.'1'im, G. 1.. 1904 The development of the cranial and spinal nerves in the
occipital region of the human embryo. Am. J. Anat., vol. 4, pp, 83-116.
 
Wr:iGN1~;R, K. 1901 Beziehnngen des Nervns accessorius zu den proximalen Spi~
nalnerven, Arl). a, Anat. Tnst., Abt. 1, Bd. 17, S. 551-587.
 
\V1NI)LE, ‘W. F. 1931 The sensory components of the spinal accessory nerve.
J. Comp. Nenr., vol. 53, pp. 115-127.
 
\Vi.\'m.E, W. F., AND 1.. C. DE LOZIER. 1932 The absence of painful sensation in
the cat during stimulation of spinal accessory nerve. J. Comp, Ni.-ur.,
vol. 54, pp. 97-101.
 
[[Category:Historic Embryology]][[Category:Neural]][[Category:1930's]][[Category:Draft]]

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