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NUCLEAR MASSES IN THE LOWER PORTION OF THE HUMAN BRAIN-STEM


by
LEWIS H. WEED
Aktiu'r TiiACY Cabot Fellow, Harvard Medical Schohl
WASHINGTON, D. C.
Published by the Carnegie Institution of Washington
1914
CARNEGIE INSTITUTION OF WASHINGTON
Publication No. 191
3^ bO
I'Ur.SS 01- OlilSON HUOS., INC.
W.\SHINGTON', D. C.
Introduclorv
SYNOPSIS.
P:igc.
5
Cliaracter of work undertaken 5
Method of reconstruction 6
Description of Transitions from Cord to Medulla 9
The anterior motor column 9
Substantia grisea centralis and formatio reticularis 11
The Individual Masses of Gray Matter If)
Nucleus fasciculi gracilis I.5
Nucleus fascicidi cuneati 18
Relation of nuclei to floor of fourth \cntricle 21
Nucleus nervi hypoglossi 24
Nucleus ate cinereae 27
Nucleus ambigiuis 31
Nucleus nervi cochlea' 32
Nucleus nervi vestibuli 33
Nucleus nervi vestibuli mediulis 35
Nucleus nervi vestibuli s])inalis 36
Nucleus nervi vestibuli lateralis 37
Nucleus nervi vestibuli superior 38
Nucleus nervi abdueentis 40
Nucleus nervi faciahs 41
Nucleus nervi trigemini 42
Nucleus intercalatus 46
Nucleus tractus solitarii 48
Nucleus of Roller 49
Nucleus funiculi teretis 50
Nucleus lateralis 51
Nucleus incertus 52
Nucleus olivaris inferior 53
Number of cells in inferior olive 62
Nucleus olivaris accessorius medialis 63
Nucleus olivaris accessorius dorsalis 65
The pontine complex 65
Nuclei arciformcs 66
Corjius ponto-bull>are 68
Nuclei pontis 70
Nucleus olivaris superior 74
Acknowledgments 76
Bibliography 76
Explanation of plates 78
A RECONSTRUCTIO-N OF THE NUCLEAR MASSES L\ THE LOWEl
PORTION OF THE HUMAN BRAIX-STEM.
INTRODUCTORY.
CHARACTER OF WORK UNDERTAKEN.
For the purj^ose of securing more accurate knowledge of the masses of
gray matter in the rhomhencejihalon, this work was undertaken, with the
idea that l^y a careful wax-plate reconstruction of the nuclear material in one
brain-stem the i)resent conception of their morphology might be advanced.
The study has been i)urely morphological, with no attempt to introduce other
elements. With the realization that considerable indi^idual Aariation exists,
even on macroscopic examination in the surface anatomy of the medulla and
pons, the conclusion becomes obvious that the mor])hological studies here
presented deal with only one brain-stem and in the finer details the findings
will not endure for all types. However, it is believed that such a study of
the form of the different gray masses in the caudal portion of the brain-stem
may prove advantageous in the ultimate establishment of the finer anatomy
and may perhaps serve as a basis for somewhat more extensive studies.
In order that the model might exhibit as many of the characteristics of
the morphology of the medulla and pons as possible, different masses were
retained in i)art on the two sides of the median raphe. In the most caudal
portions, the masses modeled are identical, but at the decussatio pyramidum
the outer limits of the formatio reticularis are modeled on the one side, while
on the other the anterior column is sharply cut off from the central gray
matter. In this way the scattered masses of the formatio are brought out,
as well as the corresjjonding separation of the anterior column from the
nuclear material about the central canal. This modeling of the formatio
reticularis is continued cephalad, so that the one side of the reconstruction
exhibits the mor]ihology of the formatio reticularis and the markings of the
floor of the fourth ventricle, while the opposite half shows the isolated nuclear
masses segregated from each other. These differences in the two halves of
the reconstruction are explained in more detail in tlie \arious descriptions
com])rising this paper.
The literature on the morphology of these nuclear structures in the human
brain-stem is wofully scant. The most important studies are those made by
Dr. Florence t^abin, of the reconstruction of the nuclear masses and fiber paths
of the brain-stem of a new-born babe. Most of the other i-eferences to the
literature deal not with actual morphology, but with i)lotted limits, and it is
to avoid such diagi'ammatic representations that this study is i)r(s(>nt('d.
6 A Reconstruction of the Nuclear Masses in
Throughout this paper, the terms "nuclear material " and " gray matter"
have been used almost synonymously. Neither of the terms is satisfactorily
descriptive, but by them are meant the collections of nerve-cells with attending
neuroglia-elements, which go to make up the easily recognizable nuclei, the
various substantias, and the formatio reticularis. Considered narrowly, these
masses are merely those in which the cellular elements i)redominatc in amount
over the fiber strands. Of the other terms used in this paper, little need be
said. "Cephalic," "superior, "and less frequently "upper" are the adjectives
applied in the sense of "toward the cerebrum," while "caudal," "inferior,"
and "lower" are used to designate the direction of "away from the cerel^rum"
or "tow^ard the tail."
METHOD OF RECONSTRUCTION.
To secure the third dimension in this morphological study, the method
of Born was adojjted reconstruction by means of wax plates of uniform
thickness. By a projection apparatus, drawings of uniform enlargement
were made from a series of sections of the human adult brain-stem. This
series of over two thousand serial sections comprises one of the "loan collections" in the neurological series of the Anatomical Department of the Johns
Hopkins Medical School. (Brain-Stem No. 2627). The brain-stem was
fi.xed in formalin, embedded in celloidin, and cut transversely, the sections
being 40 microns in thickness. The staining was done ]iy the Weigert-Pal
method, with counterstaining by carmine. In this present work every fifth
section was projected with a constant magnification of 15 diameters; the drawings were made and then corrected by examination of the slide under low
magnification; the corrected drawings were transferred to wax plates and
the plates were cut by means of a knife. The magnification of 15 diameters
was selected because it secured a i)late of convenient thickness (3 millimeters)
and also because it practically coincided with the enlargement used by Miss
Sabin in her reconstruction of the brain-stem in the new-born babe (14.5
diameters).
The sections in this series are well stained and no difficulty was experienced in differentiating between nuclear material and the fiber bundles. The
masses of gray matter were outlined with consideration chiefly for the general
appearance of the nuclear mass and with much less regard for the individual
cells comprising the mass. This differentiation on this grosser outline leads,
it is believed, to a better and truer conception of the mori^hology of the
masses. In cases where doubt existed, and in the determination of the final
limits of the gray matter under consideration, the identification and location
of the characteristic cells of the nucleus were regarded as necessary for the
correct establishment of the limits of the nuclear material. Comparison of
the results given by l)oth of these methods the first with moderate magnification, and the second with magnification high enough to i)erniit identification of characteristic cells showed that in no cas(> would the limits, as
The Lower Portion of Die Human BrainSUin. 7
obtained by consideration of the general appearance of the nuclear masses,
l)e changed by more than the thickness of one i;)late. In i:)ractically all cases
the limits determined b,y the two methods coincided. However, in order to
be certain of the limits in all cases, the drawings were carefully corrected
under magnification high enough to show both the individual cells and the
fine structure of the gray material.
One of the most important factors in securing a model which shall
present true relations and correct morphology is that of accurate i)iling of
the individual plates. The controls used for the piling of the plates in this
work were (1) the external form of the adult brain-stem; (2) the form of the
floor of the fourth ventricle; (3) sections of the brain-stem cut in the sagittal
j)lane. As, unfortunately, no drawing of the brain-stem from which these
sections were obtained had been made before cutting, the use of another brainstem, as a guide for piling, was rendered necessary. It was found that the
external form best served as the pattern for the correct piling of the i)lates
in the caudal part of the medulla, while cephalad to this the Hoor of the fourth
ventricle, together with the external form, j^roved most reliable. Sagittal
sections of the l)rain-stem from the neurological loan collections of the
Anatomical Laboratory were used as further controls, but were not considered
to be wholly reliable, because of the chance of error in the exact jilane of
cutting; for it was realized that variations in two i)lancs might occur in
these sections, the correction of which could only be worked out after considerable study and with reference to certain points assumed to be constant;
and these so-called constant ]ioints are really constant only in the transverse
diameters and can control only the jilane transverse to the long axis of the
brain-stem. Such points, c. g.. are the inferior and superior ends of the
hypoglossal nuclei, which in this series occurred in the same sections in both
instances good evidence apjjarently that the general planes of tlH> niodcl
were correct.
The lateral deviations of the model were corrected on the a.ssumption
that the anterior fisiBure of the cer^ical spinal cord and of the medulla, the
posterior fissure of the cervical cortl, and the median sulcus of the floor of
the fourth ventricle, all formed straight lines. Inspection of a number of
brain-stems led to this conclusion and it was decided that if these wqvq
considered as constant fixed lines, less error could occur in the planes of the
model than if other guides were adopted. The other planes were controlled,
as far as i:iossible, by the sagittal sections, but chiefly by the external form
and by the morphology of the floor of the fourth ventricle. One of these
transverse planes was considered (established l)y the occurrence (as mentioned above) of the caudal eii<l of botli hypoglossal nuclei in one section,
and of the posterior }^oles of the inferior olivary nuclei in another section.
With these two ]ilanes established the lateral by the fissures assumed
to be straight and the trans^'erse b}' the occurrence at tlie same knels of
the limits of corresponding nuclei the definite establishm(>nt of an antero
8 A Rcco7}struc(ion nf the Nuclear Mames in
posterior plane was to be decided. It was tliought that possibly there might
be found a constant relationship between some definite point in the tegmentum and a point in the basilar portion of the brain-stem. Many points
in several sectioned brain-stems were tested for this desired constanc.y in
relationship, but no two points could be established \\liicli maintained the
same relative positions in different brains. For the determination of this
antero-posterior jilane, which in sections of the adult lower l^rain-stem is
least imjjortant of all, the use of the external form and of the floor of the
fourth ventricle was necessary.
The wax plates were cut out along the lines indicating the external form
of the section and were then piled with reference to the three jilanes, the
whole giving a very accurate reproduction of the external form of the brainstem in its lower portion. Definite points were made on successive plates
to give the relationship of plate to plate and reconstruction of the nuclear
masses was begun. The portions of the plate to be modeled were preserved,
together with the ]X)ints to show the relationship to the adjoining plates, and
the remainder of the plate was cut away. The relations of the individual
nuclear masses to the whole were preser\-ed by means of wax l)ridges left
in the original plate, and these bridges were cut away as soon as the nuclear
mass was fixed in its position.
As far as i^ossible, no fusion of wax plates was resorted to until a considerable number of plates had been piled together. The object of this procedure was to avoid the introduction of chance variations in the j^lates, as
will necessarily occur if the fusion be done as each plate is added. Owing to
the com])lexity of the inferior olivary nucleus, such fusion had to lie done as
each ])late was added, but it is felt that additional information regarding its
complexity is probably add(Ml in this one case.
The brain-stem from which the sections used in this reconstruction were
cut was embedded in celloidin in several individual l)locks. In the ]iortion
of the series here involved tlu-ee blocks were concerned and compensation
for the tissue lost in the transition from the first to the second and from the
second to the third blocks had to be made. The second block was somewhat
distorted and to make the plates rei)resenting the second block coincide with
those of the first the magnihcation of 15 diameters had to be changed in both
antero-jjosterior and lateral dimensions. With this correction applied, the
plates of the third block with the uniform enlargements of 15 times Htted
exactly the resultant model. The corrections for loss of tissue amounted
to 2 plates on one side between sections 345 and 350: in the s(>cond instance
to 1| plates l)etween sections 700 and 705.
In the drawings of the completed reconstruction, the representations
have been made from a single viewpoint, in i)ersi)ective, which is taken from
the level of section 000. Tliis difference between jierspective and geometric
rei)re.sentation results in some foreshortening, which is most marked in the
spinal segment of the model.
The Lower Portion of the Hiiriuni BroiJi-Sfeii). 9
DESCRIPTION OF TRANSITIONS FROM CORD TO MEDULLA.
THE ANTERIOR MOTOR COLUMN.
The anterior motor column has been reconstructed in this mo(l(4 from
the upper cervical region to the point where it blends with the formatio
reticularis of the medulla. On the left side of the model (figure 2) the separation of the anterior colunm (mc) from the tegmental gray matter has
been shown, but on the right side the fine extensions of nuclear material
from the tegmental portion to the column have been included (cf. two sides
of figure 9), so that the course of the pyramids into the lateral columns in
the cord is not given. The morphology resulting from the modeling on the
right side will be discussed under the subdivision of the substantia grisea
centralis and the formatio reticularis. The j^resent portion of this communication treats only of the morphology of the isolated anterior column. The
term "anterior column" will be used throughout to designate the collection
of motor cells in the anterior portion of the gray matter of the sj^inal cord
{mc, figure 8); the term ''anterior horn" will not be used, as it does not
represent the continuous character of the cell-collection.
Figiu'e 8 shows the typical transverse section of the upper cervical cord.
In this the anterior column api)ears on section as an irregularly triangular
mass of motor cells and supporting tissue. The anterior column (me), as
modeled, is shown in figures 1, 2, and -i, dealing here with the left side of the
reconstruction. It does not present any well-defined surfaces for examination, but is probably best described from the hiteral, ventral, and mesial views
a shown in the drawings. Roughly, it may be divided here into the cervical
portion, the jjortion isolated from the gray matter ]\v the ]\vramids, and the
superior portion, in which the anterior coluniii fuses with the formatio
reticularis.
When viewed from the lateral surface (figiue 2), the anterior colunm in
its cervical portion exhibits a somewhat rounded vcntro-lateral surface,
which is sharply defined dorsally, but curves gradually around the ventral
side. Its dorsal margin is a fairly straight, sliglitly irregular projection.
Just ventral to this is a .small, elevated ridge which runs cephalo-caudally
throughout this portion. \'entral to this ridge is a very shallow longitiulinal
depression, anterior to which the rounding of the surface ventrally occurs.
The character of the column changes considerably as the region of its separation by the pyramids is reached (figure 9). The dorsal margin, at the
caudal end of this decussatio i^yramidum (cf. figure 2), is marked by irregularities, the most caudal of which becomes a well-defined dorsal spur. This
is followed, cephalad, by a convex sheet-like i)rojection dorsally, superior
to which is a shallow ventral dejiression. The cephalic l)order of this gradually inclines dorsally and then runs sharply cephalo-caudally to the suiK^rior
limit of tlie decussation. The lateral ritlge, noted in the cervical poi'tion of
10 A Reconslrudio?} of the Nuclear Masses in
the column, becomos ill-defined and irregular in the caudal portion of the
decussation, but in its superior })ortion it is accentuated as a laterally
projecting tliin sheet of cellular tissue. This curves slightly dorsally, l)ut
shows a marked ventral curving in the region just above the pyramids. The
shallow depression of the cervical portion of this surface becomes converted
into a definite furrow in the caudal half of the decussation; superior to this,
it is lacking and the surface ventral to the lateral ridge is smooth.
Superior to the decussatio pyramidum, the anterior column loses much
of its character. Its dorsal surface merges with the cephalo-ventral slope
of the formatio reticularis as this latter ]:)ecomes prolonged ventrally in the
form of a ground substance fairly free from fiber tracts. This is illustrated by
the fusion, in figure 2, of uncolored formatio reticularis with the red motor
column. This jDortion of the formatio. with its comparative freedom from
fiber tracts and its deeper staining ciualities with carmine, projects laterally
just ventrally to the substantia gelatinosa. From this point, it turns sharply
ventrally as an irregularly corrugated surface. It merges caudally with the
dorsal surface of the anterior column, first as a small bridge of typical tissue,
then intermits cephalad, to be connected by a second bridge of gray matter.
Sujierior to this second intermission is the continuous connection of formatio
with the vanishing anterior column. Coincident with the second bridge of
the formatio reticularis occurs a marked lateral projection of the formatit),
superior to which is a marked concavity in its surface. The lateral ridge of
this surface, which was so prominent in the superior portion of the pyramidal
crossing, curves sharply ventrally, cephalad to the i)yramid decussation, and
then loses its character on the lateral surface between the two bridges of
formatio reticularis. Just caudal to its cephalic termination a division of
the anterior column into two parallel masses is suggested from this surface
(figure 1). The motor cells are gradually lost in the upper part of this region
and as the interior column becomes fused with formatio reticularis the
motor cells disa])i:)ear.
Inspection of the ventral view of the modc^l (figure 1) shows the anterior
column on the left pursuing an almost direct cephalo-caudal direction, witli
a slight ce])halo-lateral deflection. The anterior column on the right side
shows a marked bowing laterally in the region of the decussatio jiyramidum.
The left anterior column is broader in the cervical region than in the two
superior portions; in its caudal portion the \-entral side is rounder, while
in the region of the pyramidal crossing it is flattened and narrowed and
al)ruptly marked off from the lateral and mesial surfaces. In the portion
cephalic to the superior limit of the decu.ssation the anterior column shows
a division into two masses of motor cells. The more mesial of these two
columns continues the direction of the primary cohiinn. These two cellcolumns are discrete and can be traced cephalad for some distance. The
motor cells gradually disai)pear and the two columns merge in that jiart of
the formatio, comparatively free from fibers, which projects ventrally. Such
The Lower Portion of the Human Rratn-Stem. 11
a division of the anterior liorn into two cell-columns suggests the embryologioal continuation of the anterior columns cephalad, to form the mesial
and lateral groups of motor nuclei.
From the mesial view (figure 4) the anterior column shows, in its cervical
portion, a smooth mesial surface, which gradually merges into the central
gray matter of the cord. Throughout the extent of the decussatio pyramidum, the ventral jiortion of the mesial surface is smooth, but the dorsal
portion is rougliened by numerous dorsal and mesial spurs. Above the
crossing, the mesial surface fuses gradually into the ventrally projecting
masses of formatio reticularis. The formatio shows a fairly smooth surface,
interrupted by a fiber tract in the caudal i)ortion. This intermission of th(>
gray matter of the formatio on the mesial surface corresponds to the intermission on the lateral surface, so that on mesial view the gray matter of
the formatio shows a hole through it. This ventrally projecting formatio
really consists of two ]:)lates, a lateral and a mesial, which fu.se above and
below, but in their middle contain a considerable fiber tract. The ])lates are
practically hber-free.
The cervical portion of the anterior column and the ])art ventral to the
decussation exhibit a dorsal surface. In the cervical cord the dorsal lateral
l^order is shari)ly converted into an irregular concavity which forms the
dorsal surfaces throughout this extent (figure 8). This is continued mesially
into a well-dehned lateral ridge which projects outward from the central
gray matter. In the region of the decussation of the pyramids the dorsal
surface is marked by irregularities and shows many dorsal and mesial spurs
projecting between the crossing bundles of the jiyramids. This surface is
eliminated as the column fuses with the formatio reticularis.
As will be seen in figure 2, the anterior column, after its fusion with the
formatio reticularis, is abruptly and arbitrarily ended in the model. This
was done for several i:)iu'poses, particularly as it was thought ath'isable to
show the olivary complex comj^letely sei)arated from the formatio reticularis
on the one side (left) and developing out of it on the other (right side of
model, figure 1).
SUBSTANTIA GRISEA CENTRALIS AND FORMATIO RETICULARIS.
The two sides of this model were reconstructed for different piu'poses,
so that on the right side the reconstruction should deal only with the unseparated masses of gray matter, outlines being drawn around the extreme
portions of the gray matter present in the series of transverse sections.
Hence, on this right side, the substantia grisea centralis, that indifferent
mass of gray matter about the central canal of the spinal cord (figures cS and
9), is modeled together with the extreme portions, such as the nucleus fasciculi gracilis, the nucleus fasciculi cuneati, the substantia gelatinosa (figures
10 and 11), etc. Tracing this gray matter about the canal cephalad, we
find it merging with the formatio reticularis of the medulla and pons, but
12 A Reconstruction of the Nuclear Masses in
this fusion is not well shown in the model because of the fact that the formatio
reticularis is surroniidefl by the nuclei which separate the formatio from the
fiber tracts which bound the brain-stem in tliis j^ortion. The central gray
matter of the cord will here be describeah as it goes cephalad to merge with
the medullary formatio reticularis, and the extreme mass of gray matter of
the cord will hv briefly commented upon.
The ty])ical cross-section of the central gray matter of the upper cervical
cord is shown in hgure 8. Here it can be seen to consist of a central body,
surrounding the central canal, and of two arms on each side projecting
from the ventral and dorsal angles of the lateral surface. Dorsally, the arm
is long and curving (eg in figure 3), constituting the posterior column with
its substantia gelatinosa. In the mid-line this arm is elevated into a very
slight dorsal ridge. The lateral surface of the central gray matter shows a
concavity extending upward into the decussatio pyramidum; this concave
sui-face results from the curve of the j^osterior arms of the central gray matter
and the mesial i)rojection of the anterior columns. The floor of this depression is very smooth except near its ventral termination in the anterior column;
here the surface is raised into a definite lateral ridge. Ventral to this ridge,
the surface slopes rapidly into the dorsal surface of the anterior column.
Anteriorly the body is characterized by a slight mid-lino ventral ridge, on
each side of whicli are concave surfaces.
The central gray matter is considerably affected by the decussatio
pyramidum. The most striking of these changes consists in the breaking
up of tlie anterior arm of the gray matter by tlie obli(iuely coursing jiyramidal fibers (figure 9). On the left side of the model, as shown in various
figures, the reconstruction was limited to the solid mass of the anterior
column and to the undisturbed portion of the central gray matter. Inspection of figures 2 and 4 shows well the resulting mori)hological changes in the
central gray matter. The ventral border is turned dorsally in a gradual
convexity, l)ut with a more rapid dorsal deflection than the central canal
exhibits (figure 4). This figure also records the marked irregular projections
of the ventral border. The lateral surface of this central gray matter shows in
its ventral jioi'tion no lateral curving because of the separation of the anterior
column, but the dorsal con\exity is continued to the ventral margin in tlie
mid-line. This ventro-Iateral surface which results is marked by many
irregular projections, most of them sliort and tliick. At a point opposite
the caudal end of the nucleus fasciculi gracilis (figure 2), the central gray
matter shows its first merging into formatio reticularis, for here it is that
the peculiar filier-free ])()rtion of the formatio l^egins to project ventrolaterally to connect finally- with the anterior colunm. This mass is separated
from the substantia gelatinosa by a very deep and narrow fissure which
ciu-ves inwardly, foHowiug the ventral curve of tlie substantia gelatinosa
(figures 1 and 2). .McsiaUy, tliese i)rojections are separated from the ventral
l)r()jection of the cciilral gray matter by a deep, and soinewhal wide, irregular
The Lower I'urtioii of Ihc JIiiiikui Jiniln-Slcin. \'.]
furrow. A more detailed description of these projections has been given in
the subdivision descrilMnji the anterior cohunn.
On the ri<i;lit side of this model, the spurs of nuclear material between
the hber bundles and the outer limits of the gray matter have been modeled.
This results in a slight fenestra in the wax, marking the crossing of the
l)yramids, while the great area of the decussation is occupied by the network
of nuclear material which lies between the fiber bundles. Such a picture of
the network is shown in figure 9. When this right side is viewed laterally,
the most striking feature is the fulness of this surface as compared with the
left. Following the dorsal margin of the anterior column cephalad, it is
seen to extend dorsally in the caudal portion of the pyramidal crossing f:)y a
series of step-like dorsal projections. It very soon fuses with the formatio
reticularis ventral to the substantia gelatinosa. From this point cephalad,
the extreme lateral wall of gray matter is solid, and exhibits certain characteristics dependent upon the level considered. The mesial surface of this
dorsal projection from the ventral horn is very rough and irregular, marked
by the outlines of the coursing jjyramidal fibers (figure 9). Inspected from
the ventral surface (figure 1), the right side shows marked irregularities in
its dorsal concavity in the region of the decussation, as well as marked
lateral bowing of tlie anterior column in this region. Above the dccussatio
pyranndum, tlie anterior i:)ortion of this gray matter of the formatio reticularis becomes markedly widened transversel}\ From the marked ventromesial border, the mesial surface slopes dorsally toward the mid-line without
irregularities. The mid-line ventral projection is not marked.
As soon as the anterior column becomes united to the ventral svu-facc
of the formatio reticularis, its lateral surface becomes marked by irregularities. A poorly defined ridge with a sharp dorsal border continues the line
of the dorsal margin of the anterior column for a short distance cephalad.
Dorsal to this are two short irregular ridges which deviate to the substantia
gelatinosa. Just above the ventral of these three ridges is the rounded
caudal shoulder of an elevation which runs cephalad, to exjiand suddenly
as the nucleus olivaris inferior develops in its midst (figure 1). A short
distance caudal to the oliva, between this eminence and the substantia
gelatinosa, is a well-defined lateral ridge, broad and smooth, which is traced
cephalad to a point slightly caudal to the cochlear nucleus. Behind this
eminence are the irregularities of the nucleus of Blumenau and around on
the dorso-lateral surface is the smooth ])late of gray matter which leads posteriorly into the tela choroidea inferior (figure 3).
The relations of the nucleus oli^aris inferior to the formatio reticularis
are of interest. The anterior column, after merging with the formatio
reticularis and losing its motor cells, becomes increased in the transverse
and dorso-ventral diameters (figure 1), showing a sudden enlargement just
caudal to the nucleus olivaris inferior. On the mesial surface of this enlargement the caudal end of the nucleus olivaris accessorius medialis develops.
14 .1 h'cconatruvtion of the Nuclear Ma.sses In
As soon as this appears, the enlargement shows a cupping for the caudal
pole of the inferior olive and the formatio reticularis recedes from it to form
a ventral surface at some distance posterior to the dorsal leaf of the olive.
This ventral surface is smooth in the main, with a slight curvature, so that
it faces for the most part mcsially as well as ventrally. The nucleus olivaris
accessorius dorsalis lies central to it, separated by a small series of fiber
bundles. The mesial edge of this surface is very irregular in its upper twothirds, while its lower one-third is in intimate relation with the dorsal margin
of the nucleus olivaris accessorius medialis. Alcove the superior mesial angle
of the dorsal accessory olive is an irregular ventral spur. The lateral border of this ventral surface of the formatio reticularis in the olivary region
shows a gentle concavity which includes the olive. It is continued laterally
into a roughened ventro-lateral plate which exhibits a very irregular dorsal
border, projecting laterally over the lateral surface of the main mass of
gray matter.
The mesial surface of this olivary portion, bordering laterally the stratum
interolivare, is fairly smooth, showing many gentle eminences.
At the superior end of the inferior olivary nucleus the lateral wall is
marked by the masses of gray matter projecting out from the vestibular
nucleus along the entering vestibular nerve. This surface is continued
upward into a mass of gray matter l.ying dorsal to the vestibular nuclei
the dorsal projections of the medial and superior portion (figure 13). On
dorsal view (figure 3) these masses are shown cut off abrujitly on the right
side of the model. Continuing cephalad, the j^rojections are seen to merge
into the dorso-lateral plates of the superior vestibular and of the trigeminal
nuclei.
The extreme lateral surface above the vestibular complex is marked
by the irregular bulbous swelling of the sensory portion of the trigeminal
nucleus. A'entral to this the wall is continued irregularly into the dorsally
projecting lateral wall of the j^ons. The mesial surface of this portion of the
general gray matter is smooth and approximates the line of the raphe, as
the median fillet assumes the transverse direction and divides the pontine
nuclei from the formatio reticularis.
The ventral surface of the formatio reticularis, in the region ce])halic
to the sui)erior pole of the nucleus olivaris inferior, shows a very striking
ventral projection. This is seen in part in figure 13. As the superior pole
of the olive recedes and vanishes, the formatio reticularis sends ventrally a
long, narrow, mesial spur and a shorter lateral spur (figure 13) ; these arc
well defined and arc^ separated by longitudinall}^ coursing fillers. These
projections surround somewhat and join with the cells of the pontine nuclei.
The mesial of the two masses does not extend cephalad for a very great
distance, as it is abi-uptly eliminated by the changing of the medial lemniscus
to its tran.sverse jjosition in the cephalic portion of tiie pons. The shorter,
thicker, lateral projection continues to carry the formatio reticularis tissue
Tlic Lower Poiiion of (lie Human Brain-Stcin. 15
toward the pontine nuclei, until the lateral wall of the pons project.s far
(lorsally. Both of these i)roj('('tions arc very irregular and are cut by fiber
bundles coursing through them and by spurs and hssures on their surfaces.
As the lemniscus medialis changes its long axis to a transverse position,
the character of the ventral wall of the formatio reticularis changes. The
mesial ventral projection is suddenly discontinued, but the deep dorsal
fissure lietween the two projections continues almost to the cei^halic bortler
of the model. This ventral surface of the formatio, lying dorsal to the
lenniiscus medialis, is roughened by slight eminences and shallow groovings.
Mesiallj' it is encroached upon by th(> nucleus reticularis tegmenti pontis.
THE INDIVIDUAL MASSES OF GRAY MATTER.
NUCLEUS FASCICULI GRACILIS.
From its inferior end, just caudal to the lower extremity of the decussatio ])yramidum, the nucleus fasciculi gracilis extends as a continuous
nuclear mass to the inferior end of the nucleus vestibularis medialis a point
on the same level with the mid-iioiut of the nucleus alse cinerea>. It measures
in the longitudinal direction 14.4 millimeters. The whole extent of the
nucleus igr) is shown in figure 3, a dorsal view, while figure 4 gives the mesial
view. Figure 9, a characteristic transverse section through the decussation
of the pyramids, shows the extent and characteristics of the nucleus in its
caudal half, while figure 10 gives a transverse section through its broader and
larger cephalic half.
In its caudal portion the nucleus lies in the midst of the fiber bundles
of the fasciculus gracilis, but the fasciculus becomes smaller above and the
nucleus correspondingly larger, so that this nuclear mass occupies the whole
of the mesial dorsal segment of the medulla (figures 3 and 10). On the mesial
surface the dorsal longitudinal fissure is in close approximation in the lower
two-thirds of the nucleus, but in the cephalic portion the mesial surface is in
relation particularly to the caudal half of the nucleus alae cinereae. Lateral
to this gracile nuclear mass are the fibers of the fasciculus cuneatus for the
caudal five-sixths of its extent, but in its more cephalic portion the cell-mass
of the nucleus fasciculi cuneati is directly lateral to it. W'ntral to the nucleus
lies the central gray matter of the cord in its lower two-thirds; in the cephalic
one-third are the nucleus alse cinereae and the fasciculus solitarius with its
accompanying lateral nuclear mass. These relations are brought out in the
transverse sections already referred to and in the figures showing the dorsal
and mesial surfaces of the model.
The dorsal aspect of the nucleus fasciculi gracilis, when reconstructed,
shows as a long mass, with the caudal half narrow and gracile while the
cephalic half broadens out in the clava (figure 3). This increase in the
transverse diameter of the nucleus is rather sudden and occurs at the cephalic
limit of the decussatio pyramidum. The most caudal portion of the nucleus
16 A lucunstnaiioii of llic Nuclear Masses in
from dorsal view shows as a rather smooth, narrow cohmm in close relation
to the dorsal fissure. The nucleus in its caudal portions has a poorly defined
mesial surface and the nuclear material extends practically to the dorsal
fissure, even though the main characteristic nuclear mass, on superficial
inspection, seems to end at some distance lateral to the furrow. Hence, on
reconstruction, the nuclear columns of both sides, representing the two
nuclei, lie in fairly close approximation in the mid-dorsal line. This mesial
dorsal edge of the two nuclei shows considerable curving, a phenomenon due
to the peculiarities in the nuclear formation, as the dorsal longitudinal fissure
was reconstructed as a straight line and served as one of the main guides
against lateral deviation. At a level with the caudal extremity of the nucleus
fasciculi cuneati, the dorsal surface of the nucleus fasciculi gracilis shows
three dorsal spurs (figures 3 and 9). The most lateral of these, bounded
mesially b}^ a deep furrow, is short and rather thin, exhibiting a tendency
to fold in a gentle curve toward the mid-line. The middle of the spurs
projects dorsally more strikingly than does the lateral, as shown in figure 2.
This middle spur arises gently from the dorsal portion of the nucleus caudal
to the inferior end of the cvnieate cell-mass and only slowly assumes the
character of a sharp spur. At its cephalic end it curves rather abruptly
mesially and loses its character in a broader mesial slope. The mesial of
these caudal dorsal spurs is very poorly defined, being constituted of a
series of imperfectly differentiated notches, as shown in figure 3. This mesial
spur can be traced cephalad somewhat further than the other two; it ends
in a small rounded knob of nuclear material. The ]ioints of cephalic termination of these three spurs constitute a fairly straight line, which runs from
the lateral spur mesially and cephalad. The lateral of these spurs, after
ending, may be considered to begin a short distance cephalad to its termination, as a fairly well-defined ridge which continues ui)ward to end in bulbous
dilatation over the broader cephalic half of the nucleus. Lateral to the
superior portion of this ridge is a deep furrow, on the outer side of which is
a small dorsal spur. The middle of the inferior group of dorsal spurs, after
a slight interruiition, is continued cephalad as a small, pyramidal projection
which ends at about the same level with the lateral spur. Mesially the third
spur is not made out. In the corresponding place, however, at the point of
cephalic termination of the other spurs, occur two small knob-like projections, both mesial to tlie middle spur.
In the middle of these upi)er dorsal corrugations, the nucleus fasciculi
gracilis widens out rather abruptly. Above their cei)lialic terminations,
occurs a slight transverse depression, cephalic to which the nucleus presents
a smooth dorsal surface. It widens very slowly in its superior half, to reach
its greatest transverse diameter at a level with the calamus scriptorius.
Here the nucleus shows as a marked and prominent mesial shoulder, corresponding to the widening out of the spinal canal into the fourth ventricle
(figure 3). Above this point the mesial dorsal edge of the nucleus rapidly
The Lower Portion of the Human Brain-Stem. 17
recedes laterally in a lateral convexity. Dorsal to this extreme mesial edge
is a second angle in the nucleus, corresi^onding to the point of attachment of
the inferior velum. This line curves around to terminate at the junction
of the mesial vestibular nucleus and the nucleus of the fasciculus cuneatus.
Lateral to the line of attachment of the velum is a broad, curving, and smooth
surface, directly underlying the surface form. This plate is, at its caudal
extremity, almost entirely comjiosed of the nucleus fasciculi gracilis, but as
it passes cephalad the nucleus fasciculi cuncati gradually encroaches upon
it, occupying it entirely at the cephalic limit of the gracile nucleus just below
the median vestibular nucleus. This encroachment determines the lateral
dorsal termination of the nucleus fasciculi gracilis.
The mesial view ( Hgure 4) of the nucleus fasciculi gracilis shows the long
transverse axis of the nucleus to be dorso-ventral in direction. Caudally,
the anterior part of the nucleus does not extend to the so-called central gray
matter. The ventral limit of the nucleus soon approaches this gray matter
and extends cephalad in a gradual curve to the opening of the fourth ventricle.
The mesial surface of the gray matter of the gracile nucleus lies slightly
lateral to the central canal and to the dorsal longitudinal fissure (figure 9).
It shows slight lateral depressions and projections, corresponding to the
curving of the mesial limits as seen on dorsal view. The most marked of
these lateral depressions occurs about the level of the sudden widening out
of the upper half of the nucleus. The dorsal limit of the nucleus, as seen on
mesial view, shows the irregularities due to the dorsal spurs already described.
These peculiarities of the nucleus are excellently shown in the mesial view
of the model (figure 4). The ventral limit of the nucleus in its uppermost
portion follows the line of the tractus solitarius, curving rather ciuickly
dorsally, as the nucleus of the tractus becomes associated with the descending
vestibular mass. The ventral edge then curves dorsally and caudally to
meet the dorsal and cephalic limit of the nucleus. Alesially, then, the gracile
nucleus extends in a slight i)rojection cephalad to its dorsal limit, showing
medially a triangular projection with the apex cejihalad between the vestibular nucleus and the nucleus tractus solitarii.
The ventral limit of the nucleus fasciculi gracilis is well defined throughout. In the caudal i^ortion the nuclear characteristics permit an easy
differentiation from the gray matter about the central canal. In the more
cephalic regions the bundles of the fibr arciformes interna? are taken as
the mesial and ventral terminations of the nucleus (figure 10). The ventral
surface in the caudal parts is almost transverse, but in the more cephalic
portions the curve of the internal arcuate fibers forms a curving surface which
looks not only ventrally but also laterally.
The lateral surface of the nucleus fasciculi gracilis is seen in figure 2,
which shows the irregular dorsal outline in the lower half, the marked bulging
of the upper half, and in part the relations to the cuncatc nucleus. The
lateral surface of the lower part of the nucleus really slopes dorsally and
18 .-i Reconstructlun of the Nuclear Masses in
laterally from the central gray matter. The ventral margin lies in a straight
line, is straight along the central gray matter for the caudal one-third of the
nucleus; then it forms, in the deep groove filled with fibers of the fasciculus
cuneatus, between the gracile and cuneate nuclei, another straight line which
continues to the point where the two nuclei are closely related on the lateral
plate, above mentioned, as the nucleus of fasciculus gracilis curves medially
to terminate.
Miss k^abin, in her reconstruction of the medulla and mid-brain of the
new-born, considers the gracile nucleus as a separate entity only in the
caudal portions, but as fusing above with the cuneate nucleus to form a
central nuclear mass a nucleus of the dorsal funiculus, which she believes
to be wholly a nucleus fasciculi cuneati. The nucleus of Blumenau she
considers as also contributing to this nuclear complex. While such a fusion
of the cephalic portion of the gracile nucleus with the cuneate nucleus could
be assumed, study of the serial sections in the adult has led to the conclusion
that the nucleus fasciculi gracilis can be divided from the nucleus fasciculi
cuneati. These limits of the nucleus fasciculi gracilis have already been
described for the adult. Miss 8abin's description of the morphology of the
nucleus fasciculi gracilis is somewhat inadequate, so that a close comparison
of the shape of the nucleus in the new-born and adult can not be made.
NUCLEUS FASCICULI CUNEATL
Beginning caudally somewhat superiorly to the mid-point of the decussatio pyramidum and extending cei)halad to the caudal limit of the cochlear
nucleus, the nucleus fasciculi cuneati presents a varied and irregular morphology. In its longitudinal diameter the nucleus measures in this adult
medulla 14.4 millimeters; the other diameters are not given, on account of
their marked variation at different levels. In this study, account is taken of
the so-called nucleus cuneatus lateralis or the nucleus of Blumenau (1891)
that collection of well-defined large cells which overlies laterally the main
cuneate cell-mass. In the reconstruction it was found that these collections
of apparently isolated cells lying in the fibers of the fasciculus cvuieatus were
connected in every case with the main nucleus, so that a division of the two
nuclei could not be made except on histological grounds. Whether such a
division has any functional or neurological importance can not be ascertained by the means of study used in this reconstruction. The two portions
of the nucleus have been modeled together and will be described as far as
possible as a single nucleus fasciculi cuneati. As mentioned in the description of the nucleus fasciculi gracilis. Miss Sabin included together the cephalic;
portions of the nuclei of the dorsal funiculus; this inclusion of the two in a
single cephalic enlargement we do not consider now justified. Tlie nucleus
fasciculi cuneati is easily differentiated from its neighboring nucleus of the
fasciculus gracilis.
The LmiHT I'oiiloii of the Ihiiniui Brain-Sff)}!.. 19
Dorsal to the nucleus fasciculi cuneati lies the fasciculus cuneatus, in
whose fiber bundles occur the cell-collections of the nucleus of Blumenan
(figures 9 and 10). In the cephalic portion of the nucleus the fasciculus
conies to lie almost lateral to it (figure 11). The nucleus fasciculi gracilis
and the nucleus vestibularis, pars desccndens, lie mesial to the nucleus (figures
3, 10, and 11). Lateral to the nucleus and in the cephalic half, ventrolateral, occurs the substantia gelatinosa of the fifth nerve. Ventrally the
nucleus is in relation with the central gray matter and with the formatio
reticularis; from the latter it is separated b.y the curving fibrae arciformes
internae. In its superior portion it is in ventral relation with the descending
portion of the vestibular nucleus, as the latter pushes the nucleus fasciculi
cuneati dorsally and laterally to its rather abrupt cephalic termination.
These relationships are for the most part shown in figures 2 and 3 {cu).
The nucleus may be described as an irregular wedge-shaped cell-mass
with corrugated dorsal and lateral surfaces and a small ventro-mesial convexity. The caudal portion of the nucleus is best seen on dorsal view (figure 3) and the cephalic half on lateral view (figure 2). This change in the
direction which the exposed portion of the nucleus takes is probably to be
accounted for by the more lateral position which the nucleus assumes as the
fourth ventricle widens out. It is also accounted for in part by the increased
dorso-ventral diameter of the nucleus in the region of the lower end of the
fourth ventricle a i)henomenon marked also by the ventral curving of the
substantia gelatinosa in this part (figure 2).
When viewed tangentially to its superficial or exposed surface (resulting
from the removal of the fibers of the fasciculus cuneatus), the nucleus is
seen to begin caudally as a blunted extremity (figure 3) on the dorsal surface
of the substantia grisea centralis and to widen gradually to its point of
greatest width at a level with the caudal end of the nucleus vestibularis
medialis. Above this, the nucleus narrows, due to the dorsal deflection of
its lateral ventral border, until it terminates above in an abrupt convexity,
where the descending portion of the vestibular nucleus becomes superficial
beneath the corpus restiforme.
The most caudal portion of the nucleus consists of a small dorsal ridge
with somewhat corrugated slopes. On cross-section (figure 9) near its most
caudal termination, the nucleus appears triangular with a slightly curving
base on the central gray matter. The dorsal ridge of this main nucleus of
the cuneate fasciculus can be traced in figure 3 throughout the caudal half
of the nucleus, above which point it is covered by and merges with the more
irregular nucleus of Blumenau. This dorsal ridge of this caudal half of the
nucleus deviates laterallj', soon after its origin, l)y the witlening of tlu; nucleus
fasciculi gracilis, but it soon assumes again and continues its straight cephalocaudal direction to the point at which it vanishes ventrally in the middle of the
nucleus. The extent of the nuclear material included between the sloping
sides which unite to form this median dorsal ridge increases somewhat as
this portion of the nucleus runs cephalad.
20 ^1 Rccondructiou nf the Nuclear Masses in
About in the middle of this dorsal ridge, in the caudal half of the nucleus,
its lateral slope becomes marked by irregularities in the form of slight furrows
and ridges. As one passes cephalad, these soon take shape in a marked
dorso-lateral projection which continues superiorly as a constituent portion
of the nucleus of Blumenau. This projection, in its lower portion, forms a
solid rectangular spur, but above, in its connection with the main cell-mass,
it becomes narrowed into a small pedicle with a broad, thin, lateral plate
lying in the midst of the fibers. This column can be traced cephalad to
the middle of the whole nuclear mass; in its upper portion it turns somewhat mesially, ending in a column of cells arising from its dorso-mesial angle
in the cephalic termination (figure 2). This new column rapidly connects
with an irregular bridge of cells, which covers the lateral aspect of the
dorsal ridge and runs to the mesial portion of the whole nucleus as it begins
to assume the dorsal plate with the nucleus fasciculi gracilis (figure 3).
Just lateral to this first dorso-lateral ridge is a ]n-ojection which begins
caudally somewhat cephalad to the first. This is in close relation to the
substantia gelatinosa (figure 2). Beginning below as a thin rectangular
mass of cells, this column rapidly widens into a rather broad lateral plate
with a small ]3edicle of cells connecting it with the main underlying nucleus
(figure 10). This plate marks the lateral limits of the nucleus and is shown
throughout its extent in figure 2. ?oon after its caudal origin it exhibits
a marked dorsal notch; then it overlies laterally, in a ventral projection,
the substantia gelatinosa. Coursing dorsally and cephalad from this ventral
projection, it finally loses its character in the broad, smooth, cephalic
termination of this lateral surface. Connected with this lateral plate,
just above its ventral projection, is an irregular triangle of cells elevated
somewhat above the main cell-mass (figure 2). The apex of this joins
the lateral plate, while its base lies just beneath (ventral) the lateral edge
of the dorsal plate. Its cejihalic margin is marked by a furrow on the ventral
side and by three irregular spurs on the dorsal; the furrow and projection
mark off the triangle from the smooth upper portion. The lateral surface
of this triangle is marked l\y a prominent gradual eminence and below by
a deep furrow. A sharp depression also occurs on its surface. Caudally,
the side of the triangle is marked by a deej) dorsal and a deeper, shari)er
ventral furrow, between which is a median ridge which projects ventrally
and somewhat caudally, to terminate near the lateral plate. In the ventral
fissure just mentioned, occur irregular lateral spurs and ridges, some running
u]) to the median ridge as it goes to terminate in a shallow groove marking
it off from the lateral i)late. The caudal limit of tlie dorsal furrow, which
delimits the lower side of the triangle, is constituted by the transverse bridge
of cells, already inentioncHl as continuing (he first dorso-lateral projection
to the dorsal i)late.
This dorsal plate, the caudal mesial part of which the luicleus fasciculi
gracilis occupies, is shown both in figures 2 and 3. It is a smooth curving
The Lower Portion of the Human Brain-Stem. 21
plate, lying superficially beneath the surface. Caudally it is wholly composed of gracile nucleus (figure 10), but at the level of the transverse bridge
of cells, in the cuneate nucleus, the plate begins to be composed of the
nucleus fasciculi cuneati. At the caudal limit of the nucleus vestibularis
medialis (figure 3) the whole dorsal plate is occupied by cuneate cells. Then,
as the descending j^ortion of the vestibular nerve develops, the dorsal plate
recedes laterally in a lateral convexity to approach mesially and terminate
ventrally to the lateral portion of the nucleus vestibularis medialis. The
lateral margin of this dorsal plate is quite irregular (figui-e 3) and overhangs
(/. p., is dorsal to) the base of the lateral surface triangle.
Above the superior transverse limit of the lateral triangle of the nucleus
fasciculi cuneati is the cephalic field of the lateral surface of the nucleus.
This is a fairly smooth area with a gradually convex upper border made
l)y the cells accompanying the descending vestibular root as they become
superficial. ^lesially the superior termination curves ventrally to the lateral
portion of the nucleus vestibularis medialis, to merge with the cephalic end of
the dorsal plate.
The ventro-lateral limit of the nucleus fasciculi cuneati, as soon as the
nucleus reaches its average dimensions, is easily distinguished, on histological
grounds, from the adjoining substantia gelatinosa (figures 10 and 11); it
forms a fairly straight line following the dorso-mesial edge of the substantia
(figure 2). Mesially the nucleus fasciculi cuneati in its caudal half is well
separated from the nucleus of the fasciculus gracilis by dense fiber bundles.
In the cephalic portion of the gracile nucleus the differentiation of the two
nuclei is not as easy, but is possible. This line of separation is curved,
following the direction of the fibers coursing between the nuclear masses.
Mesially the nucleus fasciculi cuneati shows a curving smooth surface which
looks laterally and mesially and moves somewhat dorsally as it develops
cephalad. Its convexity follows the curving internal arcuate fibers. The
mesial ventral border, separating from the nucleus fasciculi gracilis, lies just
dorsal to the nucleus tractus solitarii (cf. figures 10 antl 11). Cephalad the
mesial border is abruptly pushed laterally by the developing pars descendens
of the vestilnilar complex; its mesial border, however, maintains its convexity until it terminates superficially in the convex cephalic border of the
smooth superior lateral field.
RELATION OF NUCLEI TO FLOOR OF FOURTH VENTRICLE.
The correlation of the anatomical markings of the fioor of the fourth
ventricle with the underlying nuclear masses was first well worked out b}'
Streeter (1903). In this reconstruction, it has been attempted to show this
relationship in a slightly different manner than demonstrated by Streeter.
The work on this adult brain-stem was rendered less accurate }\\- the fact
that no drawings or photographs of the external form and of the floor of the
22 A Reconstruction of the Nuclear Masses in
fourth ventricle were made before sectioning. This, of course, gave some
difficulty in securing accuracy in the piling of the wax plates, but the errors
were to a large extent overcome by reference to the surface and ventricular
form which best coincided with the majority of the drawings of medullae
given by Rctzius. Yet in such cases one is inevitably impressed by the
extreme individual variations in the anatomy of floor which are present in a
series of brain-stems. Hence, in this reconstruction, not so much attention
can be paid to the smaller features of the anatomy of the floor of the ventricle,
but the larger structures are accurately placed and tlio rolationshi]i of the
nuclear masses to these is of importance and value. The floor of the fourth
ventricle was modeled on the right side of the reconstruction, while on the
left side the several nuclei alone were fashioned, and by comparison of the
two sides the relationship is apparent. The two sides with their nuclear
masses in relation are well shown in figure 3. No attempt will be made to
discuss here the surface markings, as nothing in the material used has value
in such a discussion, but Streeter's division of the floor will be followed.
Most important in this study is the comparison of the limits of nuclei as
found liy Streeter.
Just lateral to the median line in the caudal half of the ventricular
floor occurs a slight elevation, oval in outline, representing the cephalic half
of the nucleus nervi hypoglossi (figures 3 and 11). This is designated by
8treeter as the eminentia hypoglossi and corresponds to the eminentia
medialis trigoni of Retzius. In the lateral angle of this small oval occurs a
dorsal bulging coincident with the most dorsal projection of the twelfth
nucleus, as shown in figure 3. Above this, the nucleus nervi hypoglossi
turns toward the mid-line, terminating at about the line of transverse
division of the ventricle (in general, corresponding to a line di'awn between
the caudal margins of the lateral recesses). The mesial surface of the
nucleus nervi hypoglossi alone contributes to this elevation, as the lateral
dorsal surfaces of this nuclear mass are entirely covered by the nucleus alsE
cinerese in the caudal portion (figure 11) and by the nucleus intercalatus in
the cephalic half. The cephalic limit of the hypoglossal nucleus in this
reconstruction coincides exactly with that occurring in Streeter's diagram
of th(> ventricular floor.
Directly above the area described is a small, rather poorly defined
elevation overlying the nucleus funiculi teretis. In this brain-stem, as
mentioned in its description, the nucleus funiculi teretis is very short
and, perhaps in consequence of this, the elevation is very ill-defined. The
eminence is further affected by the occurrence of the stria? medullares; in
this adult brain-stem these stria? are almost lacking. Streeter i)ictures the
nucleus funiculi teretis as extending from just caudal to the cephalic end
of the nucleus nervi liypoglossi to a point slightly superior to the cephalic
ending of the luicleus intercalatus. The extent of the modeled portion of
the nucleus is easily seen in figure 3. It begins ccphalad to the nucleus of
The Loiver Portion of the Human Brain-Stem. 23
the hypoglossal nerve and extends but a short distance upward, always
median to the nucleus intercalatus.
Lateral to the nuclei of tlie hypoglossal nerve and of the funiculus teres
lies the nucleus intercalatus. This is represented on the surface by a rather
elongated diamond-shaped elevation lying lateral to the eminentia hypoglossi and the eminentia of the nucleus funiculi teretis, and mesial and
cephalic to the ala cinerea. While the area plumiformis extends caudally
to the calamus scriptorius, as pointed out by Retzius and Streeter, the
nucleus intercalatus shows its caudal end at the extreme dorsal projection
of the area hypoglossi, extending from this point cephalad to the nucleus
nervi abducentis. Streeter pictures the nucleus intercalatus as ending in the
area of the striie medullares, in which region the area plumiformis ends, but
in this adult brain-stem the nucleus extends considerably farther cephalad.
The cephalic portion of the nucleus then extends beyond the superior limit
of this area plumiformis.
Situated laterally to the nucleus nervi hypoglossi and to the nucleus
intercalatus, and mesially to the nucleus fasciculi gracilis and nucleus nervi
vestibularis, lies the ventricular one-third of the nucleus alae cinerei3e (figures
3 and 11). This is represented on the ventricular floor by the fovea vagi
or ala cinerea, the middle of the three original triangles in the caudal half
of the ventricle. This area shows a marked depression in the ventricular
floor in its superior portion, corresponding to the place where the nucleus
alse cinerese dips ventrally to the vestibular nucleus and nucleus intercalatus.
Caudally, the area shows a dorsal eminence, lying directly over the marked
dorsal angle of the nucleus al cinerese. No attempt has been made to
model or correlate in any way the loose vascular tissue in the area postrema
of Retzius. The cephalic limit of the nucleus alie cinerese, when related
to the anatomy of the floor of the fourth ventricle, lies ventral to the nucleus
nervi vestibularis medialis at a level with the middle of the nucleus funiculi
teretis. This corresi)onds to Streeter's cephalic limit.
Streeter gives the area acustica as that part of the ventricular floor
which lies lateral to the anterior fovea and the fovea vagi and the lateral
furrow connecting the two. This large area is divided into the median
vestibular field and a lateral cochlear region. As seen from inspection of
figure 3, these two regions are, in this adult brain-stem, occupied by th(^ two
nuclei that of the vestibular nerve and that of the cochlear nerve. Streeter
places the vestibular nucleus in his diagram of the ventricular floor as lying
entirely lateral to the lateral furrow. The median nucleus of the vestibular
nerve in the reconstruction extends mesially to the lateral furrow in the region
just caudal to the sixth nucleus, in which situation it seems on cross-section
to occupy most of the region just beneath the ventricle. In general, the
vestibular nucleus follows the gentle convexity of the lateral furrow, but in
the region just caudal to the nucleus nervi abducentis it shows a rather
marked angular convexity and concavity. Streeter does not give the cephalic
24 A Reconstruction of the Nuclear Masses in
limit of the nucleus, but as seen from dorsal view it extends to approximately
the same level with the superior end of the nucleus of the sixth nerve.
In the cephalic portion of the fourth ventricle, just superior to the area
of the strisD medullarcs, and lying somewhat lateral to the median line, is
the eminentia abducentis (Streeter) formed by the nucleus nervi abducentis
and the genu of the nervus facialis. As shown by a comparison of the
corresponding areas of the two sides of the reconstruction, the eminence
is directly dorsal to the inferior part of the nucleus of the sixth nerve
(figure 4). The genu of the seventh nerve is not shown in the model, as only
nuclear material was considered. This eminentia abducentis is continued
cephalad in a long cephalo-caudal elevation toward the aqueduct of Sylvius.
By comparison, this elevation running to the cephalic limit of the model
is seen to be overlying the indefinite nucleus incertus in its whole course.
Beneath this nucleus, in the cephalic portion, is the nucleus reticularis
tegmenti pontis, shown in figure 4, the mesial view. The fovea mediana,
having no correspondence to any underlying nuclear structures, is shown
between the nucleus incertus on the left and the eminence of the nucleus
incertus on the right. Streeter speaks of the overlapping of the sixth nucleus
by the nucleus incertus, but does not picture their relationship in his diagram
of the floor; a comparison of the findings therefore can not be made, but
it is more than likely that the limits are approximately identical.
The motor portion of the nucleus nervi trigcmini lies slightly caudal
and mesial to the cephalic ending of the vestibular nuclear complex in the
anterior fovea (fovea trigemini). This coincides with Streeter's diagram of
the terminations of the two nuclei. The overlapping of the nucleus incertus
by that part of the fiftli nucleus which lies in close relation to the brachia
conjunctiva is shown in Streeter's diagram and in the dorsal view of this
reconstruction.
NUCLEUS NERVI HYPOGLOSSI.
Arising in the central gray matter, on a level with the caudal pole of the
nucleus olivaris inferior (figure 10), 5.G millimeters cephalad to the superior
limit of the decussatio pyramidum, the nucleus of the hypoglossal nerve
extends dorsally and cephalad to terminate about the middle of the nucleus
intercalatus. It measures in this adult medulla 11 millimeters in length
and averages in transverse diameter about 1.7 millimeters. The measurements given by Streeter for the nucleus are 12.3x2.2 millimeters.
The nucleus lies in its caudal portion ventral to the central canal of
the sj)inal cord, close to the mid-line. Its mesial surface maintains throughout intimate relation to the mid-line of the medulla, and the whole nucleus
constantly lies ventral to the central canal and the widened fourth ventricle
(figure 4). In its lower three-fourths, this hypoglossal nucleus is covered
dorsally, and on the dorso-lateral surface by the nucleus aUr cinerea^ (figure
10); in the cei)halic one-third, it is capped dorsally and laterally l)y the
The Lower Puiiion of Ihv IIuiikdi Brain-Stem. 25
nucleus intercalatus. Lateral to the nucleus, throughout its extent, the
nucleus of the tractus solitarius occurs, ^'ontral to it, are the formatio
reticularis and the fasciculus longitudinalis dorsalis, with also the nucleus
of Roller in its cephalic one-third (figures 4 and 11).
Miss 1^'abin did not model the hypoglossal nucleus accurately, because
of technical difficulties, but merely rei)resented its position in her reconstruction, i^he states that the nucleus corresponds in length, however, to
the nucleus olivaris inferior. In this reconstruction of the adult medulla,
it is seen that the nucleus of the hypoglossal nerve corresponds merely to
the caudal three-fifths of the inferior olive. The hypoglossal and intercalated nuclei, on the other hand, together corresi)ond to the cephalo-caudal
extent of the inferior oli\ary nucleus.
The nucleus nervi hypoglossi may be described as an elongated column
of cells, pentagonal in cross-section, gradually increasing in size from its
caudal extremity to its dorsal angle at the eminentia hypoglossi and then
rapidly tapering to its cei:)halic pole (figure 4). It presents for examination
(in addition to its caudal and cephalic poles) five surfaces mesial, lateral,
ventral, dorso-mesial, and dorso-lateral. The characteristics of the nuclear
form are shown in large part in figure 4, a mesial view. The dorsal border
shows a marked dorsal angle at the junction of the cephalic one-fourth
with the caudal three-fourths. Above this, the border curves ventrally to
terminate just anteriorly to the nucleus intercalatus, in a rather sharp pole.
Caudally from this angle, the dorsal border slopes in a fairly straight line
caudally and ventrally; this border shows several depressions with curving
limits. In the caudal part the dorsal border dips into a rather deep ventral
depression, then projects directly caudally for a short distance, to turn
sharply ventrally, forming the inferior pole. The ventral border, from mesial
view, shows a gradual ventral bulging in its middle portion, sloping gradually
into a shallow dorsal depression cephalad and into a more abrupt dorsal
concavity caudally. In this cephalic depression lies the small nucleus of
Roller. The mesial surface lying along the raphe is smooth, but the dorsomesial surface, into which the mesial surface slopes, shows gradual irregularities due to the ventral depressions noted as occurring on the dorsal
border. In the most caudal and cephalic portions tlie mesial and tlorsomesial surfaces are fused into one gradual convexit.y.
From dorsal view (figure 3), the dorso-mesial siufaee alone is seen.
Arising as it does just caudally to the nucleus ahe cinereie, this nucleus
obscures the dorso-lateral surface in its lower three-fourths (figure 10) while
the cephalic one-fourth of the nucleus of the twelfth nerve is covered by the
nucleus intercalatus, which forms a well-defined dorso-lateral cap, closely
adhering to the cephalic dorso-lateral surface. The elevation between the
dorso-mesial and dorso-lateral faces of this hypoglossal nucleus is comi)osed
of two portions, both of which are fairly straight. The caudal three-fourths,
that portion below the dorsal angle, slopes slightly away from the mid-line
26 A Reconstruction of the Nuclear Masses in
as it ascends, while the cephalic one-fourth is turned toward the mid-line
from the point of the dorsal angle.
On ventral view, the nucleus of the twelfth nerve shows a gradual
increase in its transverse diameter in passing from its caudal to its cephalic
pole. The widest portion of the nucleus is attained in the middle of the
nucleus of Roller, cephalic to which the lateral wall of the nucleus rapidly
curves mesiallj^ to its cephalic i)ole. In the region of the nucleus of Roller,
the lateral ventral border is prolonged sharply ventrally for a short distance.
The ventral surface of the nucleus is somewhat irregular and slightly curved
in its lower two-thirds, with the convexity ventrally. It shows the single
ventral bulging and the two dorsal depressions described as occurring in the
ventro-mesial border.
The lateral surface of the twelftli nucleus in its caudal three-fourths is
fairly smooth and regular, sloping (as it ascends) slightly laterally from the
mid-line and also laterally in its dorsal portion. At the caudal end, the
nucleus shows a slight lateral bulging. Above the dorsal angle of the
nucleus, the lateral surface sloj^ies in a convexity toward the mid-line to
terminate in the cephalic i^ole. The lateral surface really loses its character
as the nucleus intercalatus caps the twelfth nucleus, for the dorso-lateral
surface here occupies the whole lateral extent of the cell-mass.
The dorso-lateral surface shows a more marked angle with the lateral
surface than does the dorso-mesial with the mesial face. The dorso-lateral
aspect of the nucleus is, in general, a flattened straight surface, larger and
more striking than the dorso-mesial surface, with a l:)roadened grooving in
the caudal one-third, due to the projection of the lateral depression upon
it. Slight ventral depressions occur on its surface, corresponding to those
seen on the dorso-mesial face. The cephalic one-fourth of this dorso-lateral
surface is in intimate contact with the lower end of the nucleus intercalatus.
Beginning as a very narrow cap on the dorso-lateral surface of the hypoglossal nucleus, this nucleus intercalatus covers the remaining cephalic
portion of the hypoglossal nucleus, gradually occupying its place as the
dorso-lateral border is pushed toward the mid-line. This causes the superior
one-fourth of the dorso-lateral surface of the hypoglossal nerve to look
laterally, dorsally, and somewhat cei)halad. This ujiper portion of the dorsolateral face is nuich wider than the other portion of its surface as it assumes
also the lateral aspect of the nucleus.
The caudal pole of the nucleus of the hyi^oglossal nerve shows as a
flattened face, pentagonal in outline, wliich lies transversely across the
medulla. This is due to the rather abrupt caudal beginning of the nucleus
in its characteristic form. The cephalic pole is sharp, lieing formed by the
approximation of the various surfaces of the nu('l(>us.
Many descri])tions of tlie nucleus nervi hypoglossi divide the nucleus
into intra-ventricular and extra-ventricular i)ortions. There is no morphological basis for such a division into two approximately equal parts and it
The Lower Portion of the Human Brain-Stem. 27
seems more sensible to consider the morphology of the nucleus in such a
reconstruction than the arbitrary division adopted by other authors without
reference to its actual morphology. The relation of this nucleus to the area
hypoglossi in the floor of the fourth ventricle has been considered under that
subdivision of this paper.
NUCLEUS AL^ CINERE^t.
The caudal extremity of the nucleus alse cinerese is situated just cephalad
to the caudal limit of the nucleus nervi hypoglossi (figures 3 and 4, ac),
at a point slightly more than 5.G millimeters above the cephalic limit of the
decussatio pyramidum. From this caudal pole, the nucleus extends dorsally
and cephalad, to become superficial under the floor of the fourth ventricle;
then continues ventrally and cephalad, with slight lateral deflection, to
terminate ventrally to the nucleus vestibularis medialis, just cephalad to the
sujiierior termination of the nucleus tractus solitarii, aliout on a level with
the middle of the nucleus intercalatus (figure 4). The extreme cephalocaudal diameter measures 11.7 millimeters and its greatest transverse measurement is 2.0 miflimeters. Streeter gives 13.5X2 miUimeters as the dimensions of the nucleus in his study.
The nucleus alse cinereiB presents varying relations in the several
portions of its extent. Throughout the caudal three-fourths of the nucleus
of the hypoglossal nerve, the nucleus alae cinerete lies dorsal and lateral to
it, covering the dorso-lateral surface of the former (figures 3, 4, 10, and 11,
oc). The nucleus intercalatus, in the cephalic half of the nucleus under
consideration, lies ventral and mesial to it until the nucleus ahie cinerea;
dips ventrally when it assumes a mesial and finally a dorso-mesial relation
(figure 3). Lateral to the nucleus alse cinereae in its caudal portion is a
small nuclear mass ])laced on the ventro-mesial convexity of the nucleus
fasciculi gracilis, and also the nucleus fasciculi gracilis and the nucleus
vestibularis medialis (figure 10). In its most cephalic portion the nucleus
tractus solitarii (Melius) lies lateral (figure 11). In its caudal beginning,
the nucleus alse cinerese is ventral to the nucleus fasciculi gracilis (figures
3, 4, and 10), but as the central canal of the cord widens out the nucleus
vagi liecomes superficial lieneath the floor, to dip finally ventrall}' to the
nucleus vestibularis medialis. Ventral to the nucleus ala? cinerese is the
nucleus nervi hypoglossi and the nucleus intercalatus. The formatio reticularis is in ventral relation in a small part of its coiu-se.
Mention has been made of a small nuclear mass lying lateral to the
nucleus alse cinerese, between it and the ventro-mesial surface of the nucleus
fasciculi gracilis. This mass of nerve-cells and neuroglia-cells forms a thin
sheet which follows the convexity of the ventro-mesial wall of the gracile
nucleus. Its dorsal border is seen from dorsal view in figure 3 and also
on mesial inspection, in figure 4. In its longest cephalo-caudal diameter
it measures 3.7 miflimeters, while its dorso-ventral diameter (somewhat
28 A Reconstruction of the Nuclear Masses in
oblique) averages 1.5 millimeters. Its other dimension is very small, as it
is a sheet of three or four cells only in thickness. The nucleus begins below,
at the same level approximately^ as does the nucleus alee cinerese. It then
extends cei)halad and dorsally, maintaining its close relationship to the convexity of the ventro-mesial surface of the nucleus fasciculi gracilis. Roughly,
it forms a i)arallelogram with a smooth mesial surface which looks also
ventrally. The cephalic border of the parallelogram is not straight, but
is curved with a cejihalic convexity. The superior cross diameter is also
slightly greater than the corresponding measurement in its caudal portion.
From the cephalo-ventral angle of the nucleus projects a well-defined spur
which runs ventrally, cephalad, and somewhat laterally. In the middle of
its cephalic half the nuclear material is divided into two portions by the
central gray matter, but quickly reunites above, the resulting separation
giving rise to fenestration of the model of the nucleus at this point. The
nuclear mass is histologically very distinct. It is separated from the nucleus
fasciculi gracilis by a thin sheath of nerve fibers, while from the nucleus
alae cinerese it is segregated by both obliquelj^ coursing fibers and by fibers
running in a longitudinal direction. The nucleus stains much more deeply
with carmine than does the nucleus alee cinereie. Xo large nerve-cells occur
in the cell-mass, but many small cells are found, together with many
neuroglia-cells. Few nerve fibrils occur in the nucleus.
A similarly differentiated nucleus, resembling this just described, is
found in the central gray matter, somewhat caudally to the inferior pole of
the nucleus nervi hypoglossi. Histologically and pyknoticallj', the two
nuclear masses are similar. They bear approximately similar relationships
to the central canal, both occurring lateral and dorsal to that structure.
No connection between these nuclear masses, placed in the central gray
matter, can be made out. On account of technical difficulties this lower cellmass was not modeled, but, as far as can be stated from the results of study
of serial sections, the lower mass also forms a somewhat similar sheet of cells,
but possesses greater thickness than does the upper collection.
The significance of these two cell-sheets is not known. There apparently
exists a very close relationship to the nucleus ake cincreae, especially in thi'
more cephalic mass.
Jacobsohn (1909) has described, under the term ''Nucleus sympathicus
nervi vagi," a cell-collection which coincides in part with the more cephalic
of the two nuclei under consideration and in part with the nucleus ake cinerene
as here modeled. His upper limit to the nuclear material is placed at a
much highei- level than found in this model. ( 'ajal has included similar cellcollections in the dorso-mesial nucleus of the tractus solitarius.
The nucleus ake cinereie may be roughly described as an irregularly
shaped, curving nucleus, with dorsal convexity, wliicli begins caudally as a
thin sheet of cells widening out in its middle portion and exhibiting an
irregular triangle on cross-section in its uppcn- jjortion. l^ecause of its marked
The Lower I'ortioH of the Hiotnin Bntln-Slcni. 29
irregularities, the nucleus presents the following surfaces, more or less limited
in extent: mesial, dorso-mesial, dorso-lateral, lateral, and a ventral border
which widens into a ventral surface.
From mesial view (figure 4) the chief characteristics of the nucleus can
be made out, as this view shows the dorsal convexity of the nucleus. Like
the nucleus nervi hyjioglossi, the nucleus ala* cinereje shows a dorsal angle,
occurring about the middle of its dorsal border. This underlies the eminence
in the ala cinerea of the floor of the fourth ventricle and is quite marked, as
shown in the drawing. Traced caudally from this point, the dorsal border
runs ventrally, caudally, and mesially to reach a jjosition close to the midline at the inferior extremity of the fourth ventricle. From this point
caudally, the border runs caudally and ventrally, but not as markedly ventrall}^ as just above. This change in direction of the dorsal border of the
nucleus results in the formation of an oblique angle with the apex dorsally.
Above the dorsal angle of the nucleus, the dorsal border is continued cephalad
and slightly ventrally and laterally, this direction taking the nucleus ventrally
to the dorsally projecting nucleus vestibularis medialis. This cephalic half
of the dorsal border shows three gentle ventral depressions, the most cephalic
being most marked and terminating in the cephalic dorsal bulging of the
superior pole.
The dorso-mesial surface is that part of the nucleus which presents
superficially beneath the floor of the fourth ventricle. It shows as a slightly
convex face on mesial view (figure 4), which in general looks mesially and
somewhat dorsall.y. It is marked off from the mesial surface by a change
in the planes of the surfaces which causes a slight angle to be formed in the
shape of a continuous line running from the ventricular limit of this face
downward and ventrally in a gradual dorsal convexity. This forms the base
of a triangle w^hich the dorso-mesial surface composes. The line between the
dorso-lateral and mesial surfaces at the inferior limit of the ventricular
portion of the nucleus splits into two lines a direct caudal line, short and
marking the ventricular limit, and a prolonged, indefinite, ventrally curving
line which goes to the caudal limit of the nucleus. Between the two lines is
a small, smooth, irregularly' triangular surface which looks directly mesially.
Between the dorsally convex line separating the dorso-mesial surfaces
and the ventral border is the irregularly shaped mesial surface (figure 4).
In its cephalic portion this surface looks almost exactly mesially, but a
gradual rotation occurs, so that in the lower jiortions the surface looks
obliciuely ventro-mesially (figure 10). The upper extra- ventricular portion
of the surface is narrow and somewhat triangular, the apex of the triangle
being contained in the cephalic enlargement or knob. Below this narrow
upper portion the nucleus forms a fairly accurate elongated rectangle, narrowing somewhat, however, in the caudal portion. The surface is marked
by several rather superficial grooves and by one gradual but somewhat
extensive dorso-lateral depression just caudal to the middle of the nucleus.
30 A Reconstruction of the Nuclear Masses in
The dorsal border at its caudal extremity is continued at almost a right
angle in the short, straight caudal border which extends in a ventral and
lateral direction. This is rather abruptly rounded into the ventral border,
which runs cephalad, with dorsal and lateral deviations. The ventral border
is by no means straight. For a short distance after its caudal inception, it
parallels the dorsal border, then loses most of the dorsal deflection as the
nucleus widens. This change of direction results in a marked dorsal notch.
Superior to this, the ventral border continues in a slightly irregular line to a
]:)oint just above the level of the dorsal angle of the nucleus, where it shows a
ventral bulging and thickening, due to the dorsal convexity of its border
cephalic to this. This dorsal convexity of the ventral border, more marked
at its ends than in its middle, is continued into a ventral projection of the
nucleus just below the cephalic termination of the nucleus tractus solitarii.
Above this ventral beak-like projection the ventral border curves abruptly
dorsally into the superior pole of the nucleus. Just cephalic to the ventral
bulging of the nucleus about its middle portion, the ventral border splits
into a second line, which runs cephalad in a slight, dorsally convex margin.
Between this margin and the real ventral border occurs a triangularly
shaped ventral surface. The apex of this triangle lies in the ventral projection in the cephalic portion of the nucleus; the base is formed by the
border between the mesial and ventral surfaces. This line of junction
between these two surfaces continues upward, to end in a small ventral spur
which lies mesial to and projects somewhat ventrally to the ventral cephalic
border. This ventral surface shows a fairly smooth curving face, the convexity being dorsal and lateral.
The dorso-lateral surface of the nucleus ala; cinerese is found only in
the cephalic one-third of the nuclear mass (figure 3). It is a small irregular
surface, just ventral to the dorsal border, narrower above than below, and
jjossessing an irregular anterior border. This margin is composed of the
ventral-lateral projections of the nucleus around the tractus solitarius, which
is almost inclosed by two horns of this nucleus. This margin is irregular,
but maintains a direct cephalo-caudal direction. Below, at the j miction of
the cephalic one-third and the caudal two-thirds of the nucleus, is a deep
sulcus which separates it from the mesial surface. In the upper portion the
dorso-lateral surface looks dorsally and somewhat laterally, but by a gradual
rotation the surface in its caudal portion looks laterally and only somewhat
dorsally.
The lateral surface of the nucleus is a very irregular but, in general,
smooth area which is embraced between the ventral border, the lower twothirds of the dorsal border, and the ventral margin of the dorso-lateral
surface. Cephalad, it is a concave depression which surrounds the dorsomcsial aspect of the tractus solitarius. The horns of this embracing surface
arc the ventral margin of the dorso-lateral surface and the ventral border
of the nucleus. The surface begins mcsially and cephalad on the lateral
The Lower Portion of the Human Brain-Stern. 31
aspect of the mesially projecting, cephalic knob and then curves laterally
and caudally. The surface shows a slight depression in its middle and a
very large and rather deep depression just above and connecting with the
sulcus which delimits the dorso-lateral surface. Below the sulcus the lateral
surface is large and smooth, pentagonal in outline. The angles of the
pentagon are formed by the junction of the sulcus with the dorsal margin,
by the dorsal angle of the dorsal margin, bj^ the ventral l)ulging of the ventral
surface and the two caudal angles. In its cephalic portion, the lateral face
looks laterally and somewhat ventrally, but in the caudal one-third of the
nucleus the surface is directed almost wholly laterally. This change in
direction of the surface is due to the narrowing of the dorsal, thickened
portion of the nucleus, showing on the lateral face as a caudal and mesial
sloping of the lower portion of the surface from the widened and thickened
middle portion. The lateral surface shows a curving of its whole face with
the convexity mesially. This curving is accounted for by the more lateral
position of the upper portion of the nucleus in its cephalic two-thirds.
The greatest antero-posterior diameter of the nucleus occurs at the level
of the dorsal angle and middle ventral bulging (figure 3). Both above
and below this, the diameter is maintained with liut gradual diminution.
The nucleus exhibits its greatest transverse diameter, or is thickest, at the
same level. Caudal to this, the nucleus rapidly becomes a thin sheet of
cells, while in its superior portion it maintains a considerable transverse
diameter.
NUCLEUS AMBIGUUS.
The adult nucleus ambigvuis, as modeled on the left side of this reconstruction, consists of two main masses separated by a considerable intermission (figure 4). The lower cell-mass oval with its longer axis parallel
to that of the substantia gelatinosa is found on the level of the middle of
the true hypoglossal nucleus in a plane slightly cephalic to the caudal end
of the dorsal accessory olivary nucleus. It is very small and the large motor
cells can be identified only through a few sections in this region. The main
column of cells in the nucleus ambiguus begins on a level with the middle of
Roller's "small cell hypoglossal nucleus," caudal to the cephalic ends of the
nucleus nervi hypoglossi, the nucleus alse cinerea?, and the nucleus olivaris
accessorius dorsalis. It is surrounded by the formatio reticularis, in which
it lies; lateral to it is the substantia gelatinosa, and ventral are the dorsal
accessory olive and the dorsal leaf of the main olive. Dorsall}^ it is in relation to the nucleus tractus solitarii, the nucleus nervi hypoglossi, the nucleus
alse cinereae, and in the upper part the nucleus intercalatus and the nucleus
vestibularis medialis. Cephalad the nucleus extends to a level just below
that of the caudal pole of the nucleus nervi facialis. The whole nucleus is
shown in figure 4, a mesial view of the model. Between the level of the
smaller nuclear mass and the upper nuclear column an occasional large motor
32 ^4 Rec()iislni(ii()ii of (he Nuclcdr Alasses in
cell can be made out in the sections, but these cells have not been included,
the model being onl^' of those cells which show a characteristic grouping.
The superior cell-column in the nucleus ambiguus (figure 4) begins
caudalh' as a verj- small column of cells, which rapidly widens into an oval
cell-mass with the long, transverse diameter antcro-posteriorly, but with
the dorsal end slightly drawn toward the mesial line. Directly above this
is a marked constriction, superior to which begins the main division of the
cell-column. This is oval on cross-section, the long axis coinciding with the
long diameter of the lower cell-mass. This main division progresses upward,
widening somewhat at first, but soon gradually narrowing into a second
constriction. Cephalic to this constriction is a small dilatation of the
nuclear column, above which a third constriction occurs. The cells in the
constriction increase in number and in distribution as one goes cephalad,
the result being a slightly increased size of the column. This gradually
narrows and tapers off into the cephalic termination of the column of cells.
The cephalic ending concerns only a small column of cells, but is well defined.
NUCLEUS NERVI COCHLE/E.
In the new-born medulla Dr. 8abin found that the nucleus of the cochlear nerve was rectangular in outline, with a thick ventral portion and a
thin dorsal layer lying against the surface of the corjius restiforme.
The cochlear nucleus in the adult shows most of its characteristics on
lateral view (figure 2). Lying lateral and, in j^art, ventral to the corpus
restiforme, the nucleus contributes in part to the wall of the lateral recess
of the fourth ventricle. Dorsal and mesial to the nucleus lies the corpus
ponto-bulbare (Essick).
The lateral view (figure 2) of the cochlear nucleus reveals a large ventral
parallelogram, from the spinal end of which the dorsal nucleus projects
around the corpus restiforme. The ventral border is irregularly notched:
the most cephalic of the notches corresponds to the entering root fibers.
Below this notch the ventral border slopes caudalwards and dorsally to
turn abruptly, at the inferior limit of the nucleus, into a fairly straight dorsoventral border. This straight caudal border, bending in the direction of the
lateral limit of the corpus restiforme, curves cephalad to form the dorsal
and mesial limit of the dorsal nucleus. The cephalic border is fairly straight
in its dorsal half, with a general dorso-ventral direction, but with the ventral
end slightly cephalad to the dorsal. About the middle of this cephalic border
there occurs an abrupt turn cephalad, then a right-angled defiection ventrally, resumed in a general cephalic direction, parallel to the ventral border.
The ventral broader and larger portion is further separated by a right-angled
elevation of the dorsal portion continuing the dorso-ventral line from the
middle of the cephalic border. This gives the a]ipearance as if the ventral
nucleus were inserted into the dorsal portion. \\\\]\ some histological proof
and the peculiar morphologically suggestive separation, the segregation of
The Lower Partidii of the Iluinan Brain-tStciii. 33
a ventral portion of the nucleus from the dorsal may be made, although it
must be realized that the dorsal and ventral nuclei are undoulitedly the
same continuous cochlear complex.
On dorsal view (figure 3) the nucleus shows the cur\ing about the corpus
restiforme and the very considerable transverse diameter of the nucleus.
The groove suggesting the separation into ventral and dorsal nuclei is here
readily seen. The ventral portion of the nucleus on this view shows as a
triangular mass on cross-section, with the apex dorsal. This line of the
apices lies in about the middle of the ventral mass and continues caudally
below the point of origin of the fissure between the two parts of the nucleus.
Over the lateral surface of the dorsal nucleus is a rather long and thin strip
of nuclear matter similar to that of the nucleus.
On cephalic view, the most striking feature of the nucleus not shown
on the other views is a marked hollowing of the superior surface of the
ventral portion. The cephalic line, which shows on lateral view in this
ventral j^ortion of the nucleus, abruptly plunges medially into the smooth
slope which forms the lateral nuclear wall of this fiber hollowing. The
cephalic notch observed on the ventral surface is connected with this hollowing and the mesial wall is formed from the medial angle of the notch projecting dorsally and somewhat cephalad. On cephalic inspection also the
transverse thickness of the nucleus can be made out. In the dorsal portion,
the transverse diameter is about the same as the cephalo-caudal, but in the
so-called ventral nucleus this transverse diameter is but two-thirds the
cephalo-caudal diameter. The cephalo-caudal diameter of the ventral
enlargement of the nucleus is thrice that of the dorsal projection.
Mesially the nucleus shows a fairly smooth curving outline, conforming
to the lateral curve of the corpus restiforme.
NUCLEUS NERVI VESTIBULI.
In figure 3 is given the best idea of the general form of the nuclei of the
vestibular nerve. The whole nuclear complex is shown more or less as a
unit mass, extending from the cephalic limit of the nucleus fasciculi gracilis
to the nucleus of the fifth nerve. In this ceplialo-caudal diameter the nucleus
of the vestibular nerve measures 14.7 millimeters. Its greatest transverse
diameter, occurring on a level with the so-called ventral cochlear nucleus,
measures 6.0 millimeters.
Study of the nuclei of the vestibular nerve has led to the conclusion
that the individual cell-collections should really be considered only as parts
of the main vestibular complex. ISIiss Sabin, in her reconstruction of the
nuclei from the brain-stem of the new-born babe, divided the nuclear matter
into two main masses the cell-mass median to the vestibular tract (including the descending and ascending roots) and the cell-masses lateral and mesial
to the tract and main cell-mass (the two composing the nucleus ner\i vestibuli lateralis). The main cell-mass Miss Sabin then described under the
34 A Reco7istruction of the Nuclear Masses in
divisions of the mesial, superior, and spinal nuclei of the vestibular comjjlex.
Her reconstruction led to a much simpler and better idea of the vestibular
complex than did her earlier contribution on the subject. In this reconstruction it was attempted to maintain, as far as possible, this more simple
conception of the vestibular complex, as is undoubtedly justified on morphological if not on histological grounds. The nucleus nervi vestibuli lateralis
has not in this study been separated from the median nucleus, as it was felt
that any attempt to separate this group of motor cells could only result
in the establishment of arbitrary lines of division. The separation of the
nucleus nervi vestibularis spinalis (radix descendcns) was, however, made,
as this division is one upon which unanimity could be secured. The nucleus
nervi vestibuli superior, comprising as it does the cephalic prolongation of
the median nucleus, shows no caudal separation from the main nuclear
mass. This coincides with Miss Sabin's reconstruction of the mass. As
far as possible the description of the whole nuclear mass will be made from
the standpoint of one cell-mass, but consideration will be taken of the
divisions of the nucleus into its well-established four chief nuclei.
The dorsal surface of the vestibular complex lies beneath the floor of
the fourth ventricle in the vestibular portion of the acustic triangle (figure 3). It is overlaid on its caudal portion by the gray matter and fibers
comprising the ventricular lip of the corpus ponto-bulbare. Mesially the
vestibular nucleus lies in relationship to the nucleus alai cinerese (figure 11),
the nucleus intercalatus, the nucleus nervi abducentis, and the caudal joortion
of the nucleus incertus. On the dorso-lateral side of the superior half of
the nucleus lies the brachium conjunctivum. Laterally we find the nucleus
fasciculi cuneati, the corpus restiforme, and the brachium pontis, separating
off the nucleus nervi cochleae and the corpus ponto-bulbare. Ventrally there
occur the long substantia gclatinosa, the nucleus tractus solitarii. and the
formatio reticularis. These relationships are easily understood from inspection of figures 2, 3, and 4.
The main vestibular nuclear mass, when viewed from the dorsal surface
(figure 3), as one passes from its caudal portion, exhibits a sudden widening
in the region of the middle of the nucleus, corresponding to the lateral recess
of the fourth ^entricle. This relationship is well shown in Miss Sabin's
reconstruction. Above this the main mass shows a sudden narrowing in
the region of the lower end of the nucleus nervi abducentis and a second,
just superior to this, where the fibers of the seventh nerve force the nuclear
material from the median line. Above this more caudal constriction, the
superior nucleus of the nerve may be said to lie, as it corresponds laterally to
the level of entrance of the nerve root and the division into ascending and
descending fibers. The most lateral projection of the whole nucleus represents the lateral collection of motor cells, comprising in part the nucleus
nervi vestibuli lateralis. From the cephalic j^art of the median and from
the superior nucleus, dorsal spurs and columns of cells lie in relationship to
The Luwer Portiun of the Human Brain-Stem. 35
the brachium conjunctivum. Lateral to the caudal portion of the median
nucleus (figure 3) lies the radix descendens with its accompanying nuclear
material, forming the nucleus nervi vestibuli spinalis. From lateral view
(figure 2), the general triangular shape of the nucleus can be made out. The
apex of this triangle projects laterally and ventrally to meet the incoming
vestibular nerve. With this brief general conception of the whole nuclear
complex we may proceed to a more careful description. The whole nuclear
mass may be said to exhibit three surfaces for examination: dorsal, mesial,
and lateral. The ventral surface is lost in the sloj^ing of the ventral surface
into the lateral. These surfaces will be described under the various nuclei
comprising the complex.
NUCLEUS NERVI VESTIBULI MEDIALIS.
This portion of the nucleus extends from the cephalic limit of the gracile
nucleus to the caudal border of the nucleus of the sixth nerve (figure 3).
Laterally it is bounded by the nucleus nervi vestibuli spinalis in its caudal
half and in its cephalic half by the corpus restiforme, except in the region
of the nucleus nervi vestibuli lateralis. The nucleus may be divided, for
description, into a narrow caudal half and a widened cephahc portion. On
dorsal view (figure 3) , the nucleus shows a fairly smooth surface which .slopes
ventrally toward the mid-line. Beginning below as a narrow strip of nuclear
material with its long axis dorso- ventrally (figure 11), the nucleus widens
but slowly in its caudal half. At the region of the opening of the lateral
recess into the fourth ventricle, it abruptly projects laterally, almost attaining
the mesial limit of the dorsal cochlear nucleus and covering dorsally the
radix descendens. As the opening of the lateral recess closes cephalad the
nuclear surface under the ventricular floor narrows (figure 12). When
viewed dorsally (figure 3) the mesial border of the nucleus exhibits a cephalocaudal direction with a deflection toward the mid-line as it ascends. In the
region of the cephalic pole of the nucleus nervi hypoglossi (widest portion
of the nucleus intercalatus) the mesial border of the median vestibular cellmass shows a marked lateral notch. Above this is a slight transverse
elevation across the nucleus as it widens out. At the lower limit of the sixth
nucleus the mesial border curves rather sharply laterally and then turns
cephalad again for a short distance. But from the point of occurrence of
this lateral deflection this main vestibular cell-mass is considered as the
superior nucleus. The lateral border of the median vestibular nucleus, after
the short caudal portion which ascends almost parallel to the mesial border,
runs cephalad and somewhat laterally. It is, in the main, a fairly straight
border showing some irregularities, especially one gentle lateral projection
just cephalic to the ventricular portion of the corpus ponto-bulbare. This
lateral margin continues as a smooth, straight surface to the formatio reticularis in a direct dorso-ventral direction the line of separation from the
nucleus spinahs of the nerve. At the caudal limit of the lateral recess the
36 .4 Reconstruction of the Nuclear Masses in
lateral border of the median nucleus curves directly laterally for some
distance, then abruptly cei)halad. This curving forms a lateral shoulder to
the nucleus which approaches the dorsal cochlear cell-mass. Ascending, the
lateral border again leaves the mid-line in a beak-like projection into the
most lateral portion of the main cell-mass, the nucleus nervi vestibuli lateralis.
Higher uj) the lateral margin continues straight cephalad, with a slight mesial
slope, into the lateral border of the superior nucleus. Just mesial and
somewhat cephalic to the projection constituting the lateral nucleus, the
dorsal projection of the nucleus appears. This shows a prominent caudal
margin which overhangs the main dorsal surface and curves into a sharp
mesial border, receding above (figures 2 and 3). The dorsal projection is
marked laterally by a slight ridge which terminates below in a marked dorsal
spur. Between these borders is an irregular concavity (corresponding to
the outline of the brachium conjunctivum) marked by two fenestrations
(figure 3) in the nuclear material, through which large fiber bundles course.
Just inferior to the caudal margin of the dorsal elevation is a marked space
or hole separating the lateral nucleus from the mesial a space resulting
from failure to model the fiber bundles. Mesial to the depressed opening
for this fiber bundle is a slight ridge on the mesial cell-mass.
The mesial surface of the nucleus nervi vestibuli medialis is well-defined
and of a marked mesial convexity in the caudal half. In its wider cephalic
portion the nuclear surface is poorly defined and is apparently a direct dorsoventral surface, sharply limited from its dorsal and ventral aspect. The
surface is widened considerably at a point on a level with the nucleus nervi
vestibuli lateralis, but this widening is gradual and not abrupt.
The ventral surface is somewhat poorly marked in the caudal portion
as the mesial curve is continued upon it. In the cephalic half it is fairly
regular except for the elevation corresponding to the widening mentioned
as occurring in the mesial surface. The ventral surface looks also mcsially
and in its sujierior portion passes directly into the lateral surface, being
marked by de])ressions and irregularities along the line of its relationship
to the substantia gelatinosa. In the caudal half the ventral surface terminates with its junction with the nucleus nervi vestil:)uli spinalis.
From lateral view (figure 2) the prominent features of (he median
vestibular nucleus are the dorsal projections of the cephalic part of the
nucleus and the marked overhang (dorso-lateral projection) of the nucleus
as it underlies the floor of the entrance to the lateral recess of the foin-th
ventricle. The gradual and complete fusion of the four nuclei in the complex
is well shown in this view.
NUCLEUS NERVI VESTIBULI SPINALIS.
The radix descendens, with its accompaniment of iniclear material, has
been modeled throughout its extent, even tliough in the more caudal portions
the greater part of the tract was composed of fibers and not of gray matter,
The Lower Portion of the Human Brain-Stem. 37
It ends as a thin mass, lying with its long axis dorso-ventrally, lateral to the
median vestibular nucleus (figure 3). Its caudal termination is just cephalic
to the caudal ending of the nucleus just mentioned. In the first part of
its course, the nucleus spinalis is covered dorsally by the nucleus fasciculi
cuneati, but as one passes cephalad it soon presents dorsally, as a thin
column just lateral to the caudal portion of the median nucleus (figure 3).
Its mesial and lateral surfaces in this portion are fairly straight, the mesial
well defined, but the lateral poorly differentiated from the nucleus fasciculi
cuneati. It spreads out in its ventral portion, so that on cross-section the
nucleus shows as a triangle (figures 11 and 12). As the lateral recess opens
into the ventricle the median nucleus overlaps dorsally the spinal nucleus,
which has gradually displaced laterally the nucleus fasciculi cuneati. Just
cephalic to this overlapping, the nucleus spinalis becomes superficial beneath
the corpus restiforme, occui^ying the region cephalic to the convex superior
end of the nucleus fasciculi cuneati. On cross-section in this area the radix
descendens of the nerve lies median to the former, being capped laterally
by a dense sheet of nuclear material. Figure 2 shows the nucleus spinalis
occupying the whole lateral field dorsal to the substantia gelatinosa. It
shows in its lower portion a considerable depression, but soon widens laterally
as the dorsal spurs appear on the median nucleus. The lateral border of
this surface is at first coincident with the dorsal margin of the substantia
gelatinosa, but (as the vestibular nerve enters) this lateral border of the
spinal nucleus projects laterally and ventrally to form the apex of a large
triangle comprising the whole lateral surface (figure 13). The nuclear
material comprising the cell-sheath of the nucleus is composed of a caudal
(more mesial) column and a cephalic (more lateral) column (figure 2).
Between these the nerve enters the nucleus and separates it from the substantia gelatinosa. The ui^per cell-column slopes caudally, laterally, and
ventrally from its origin in the sujierior nucleus; and so the spinal nucleus
terminates in the somewhat irregular line of the accompanying cell-columrt
as the vestibular nerve enters the brain-stem. These cell-columns about
the nerve fuse in jiart at their ventro-lateral terminations with the cells of
the corpus ponto-bulbare. Whether the cell-columns shoukl be considered
as vestibular or as part of the corpus is not wholly clear, but their histology
and position argue strongly for inclusion in the spinal vestibular nucleus,
as they hold analogous position to the cells in the radix descendens. Such,
then, is the form of the nucleus nervi vestibuli spinalis a small, thin leaf
in its caudal portion, widening laterally to its base along the entering vestibular fibers.
NUCLEUS NERVI VESTIBULI LATERALIS.
With its clearly defined collection of large cells occu])ying the most
lateral portion of the main vestibular cell-mass, the nucleus n('r\i vestibuli
lateralis exhibits a more or less characteristic form. On the lateial side of
38 A Reconstruction of the Nuclear Masses in
the main nuclear form the nucleus of Deiters shows a sharp caudo-lateral
angle (figure 3) and a definite border ascending from this. Ventrally a
sharp curve takes the cell-collection toward the mid-line. The lateral
aspect (figure 2), shows this lateral wall curving sharply mesially and somewhat ventrally, to lose its character as the cells pass mesially through the
lateral portion of the spinal nucleus. It is not a well-defined area at all and
would not be differentiated on morphological grounds. It is merely a
curving cap of cells over the lateral aspect of the medial vestibular nucleus.
Tracing the cell-mass toward the mid-line, we find only scattered cells for a
slight distance mesially, but these larger cells again become somewhat
clumped as one approaches nearer the raphe. This increase in size of the
cell-mass is represented in the form of the mesial vestibular nucleus by the
eminence or smooth elevation on its ventral surface. As they approach the
mesial surface of the medial nucleus, these motor cells become somewhat more
scattered and the cell-mass curves dorsally to end in the medial nucleus.
With such a morphology the nucleus lateralis of the vestibular nerve can
not be regarded as more than a group of large cells Ij^ing upon the lateral
and ventral surfaces of the medial vestibular nucleus and modifying in
slight degree the external morjihology of this chief nucleus. Miss Sabin
in the new-born was able to make out a lateral and mesial cell-mass as constituting this nucleus of Deiters, but here in the adult the ventro-lateral
portion is more developed with the mesial enlargement merely a scattering
of the cells in the medial vestibular nucleus.
NUCLEUS NERVI VESTIBULI SUPERIOR.
Miss Sabin was unable to model completely the superior nucleus of the
vestibular nerve, as some of it was destroyed when the cerebellum was cut
from the brain-stem. In general she pictures the nucleus as being a tapering
superior extremity of the median vestibular complex, with its medial surface
parallel to the raphe. With this morphology this reconstruction of the
adult nucleus coincides in the main. The nucleus represents the sujierior
j)ortion of the medial and also the spinal nucleus, with the dorsal projections
more prominent than the mesial portion beneath the ventricular floor.
Cephalad the nucleus ends at the caudal extremity of the main nucleus of
the fifth nerve, as shown in figures 2, 3, and 4. Tlic nucleus can best be
described by consideration of the various surfaces of the other nuclei which
pass into the superior nucleus.
When viewed dorsally (figure 3), the greater part of the superior nucleus
appearing is that which lies just ventral to the brachium conjunctivum.
The dorsal surface of this nucleus, underlying the floor, is quickly rendered
very narrow by the two lateral deflections of the mesial border of the whole
cell-mass the inferior at the caudal limit of the nucleus nervi abducentis
and the superior at the corresponding point of the nucleus incertus. This
superior angle makes room for the outward coursing fibers of the seventh
The Lower Portion of the Human Brain-Stem. 39
nerve. From this point upward to the superior termination of the nucleus,
the ventricular mesial surface is represented merely by a small mesial ridge,
irregularly marked by projection and depression. This ridge occupies the
lateral angle of the ventricular floor. Dorsal to this is the cell-mass which
lies ventral to the brachium conjunctivum. Ventral to the ridge is a solid
cell-mass which continues upward the oblique ventral surface of the medial
nucleus. This surface runs cephalad, somewhat irregularly marked by
smooth eminences, to end at the general level of cephalic termination of
the nucleus. It lies ventral to the caudal spur of the motor cells comprising
the main motor nucleus of the fifth nerve. This surface is fairly well separated from the substantia gelatinosa by a deep groove, crossed by many
fiber bundles.
The lateral surface of this nucleus presents the shape of a triangle,
with the base composed of the superior cell-column which accompanies
the entering vestibular nerve. The medial side of the triangle is composed
of the dorsal edge of the nucleus while the lateral side is the lateral limit of
the nuclear material as it gradually recedes from the entering root. Figure
2 shows well this triangular shape, placed just cephalad to the ventral
cochlear nucleus. The cell-column which projects caudally, laterally, and
ventrally from this superior nucleus to the entering nerve is ciuite irregular
in form, narrowing at its lateral extremity and widening as it approaches
the nucleus. It lies in close relationship to the substantia gelatinosa as it
nears the nucleus and forms a lateral wall which soon fuses with the ventral
wall of the superior nucleus. As it approaches the cephalic limit, this
lateral wall is continued laterally (at the ventral angle of the dorso-lateral
face) into a long spur with a dorso-mesial projection (figures 2 and 3). Ventrally this spur is composed of a fairly large knob-like swelling. Cephalic
to this spur a deep fissure runs almost directly transversely, separating the
nucleus from that of the fifth nerve (figure 3). As one views this dorsally,
the furrow is seen to become much less deep in its mesial extent and the
separation at this point is made with considerable difficulty. This dorsolateral surface of the superior nucleus represents the superior continuation
of the vestibular nuclear material which underlies the brachium conjunctivum. On dorsal view (figure 3), this portion of the superior nucleus
is characterized by a large dorsal projection at its caudal limit on a level
with the caudal extremity of the sixth nucleus (figures 4 and 13). Above
this smooth eminence, the surface plate enlarges mesially and laterally,
with a rotation so that the surfaces face in a dorso-lateral direction. The
superior portion of this surface is smooth, but the inferior and lateral parts
are marked by irregularities in the shape of small elevations and depressions,
with ridges and furrows also apparent. With the exception of a projection
at the side of the marked dorsal eminence at the level of the sixth nucleus
the mesial edge of this surface is straight, though it shows some slight
irregularities.
40 A Reconstruction of the Nuclear Masses in
On account of the thinness of this dorsal leaf, the mesial edge is fairlysharp as one passes upon its ventro-mesial surface. The leaf, however,
rapidly increases in thickness as it goes toward the main cell-mass, reaching
its greatest transverse width at the irregular ridge underlying the lateral
angle of the ventricle.
NUCLEUS NERVI ABDUCENTIS.
With its inferior termination just caudal to the ccjihalic end of the
nucleus intercalatus, the nucleus nervi abducentis extends almost to the
cephalic limit of the nucleus vestibularis (figures 3 and 4). It measures in
the long cephalo-caudal diameter 3.8 millimeters; in its dorso-ventral, 1.7
millimeters; and in the greatest transverse, 2.3 millimeters.
Mesial to the nucleus are the genu of the seventh nerve and the fasciculus longitudinalis medialis (figure 13). Dorsal to it in its middle is the
loop of the seventh nerve, while above it is covered by the nucleus intercalatus (figures 3 and 13). The nucleus lies fairly superficial beneath the
eminentia abducentis of the floor of the fourth ventricle. Lateral to the
nucleus lie the nucleus vestibularis medialis and the emergent root of the
seventh nerve. The abrupt notch made in the vestibular cell-mass to
accommodate the nucleus is shown in figure 3. Ventral to the nucleus is
the formatio reticularis. Just caudal to its inferior pole is found the nucleus
vestibularis medialis, while slightly mesial to this is the cephalic pole of the
nucleus intercalatus.
Miss Sabin describes and pictures the sixth nucleus in the new-born
as an "almost round body." The general shape of the nucleus in the adult,
as seen in figure 4, is that of an oval body with a dei)ressed mesial edge and
a bulging lateral border. The portion of the dorsal surface of the nucleus
not obscured by the nucleus incertus is shown in figure 3. The most dorsally
prominent portion of the nucleus is just superior to the caudal limit; it
shows as a projecting ridge on the dorsal and mesial surfaces (figure 4).
Cephalic to this margin, the mesial and dorsal surfaces are depressed, to
give room for the looping fibers of the ncu'vus facialis. The dejiression on
the dorsal surface persists, as is shown by the gradual ventral slope of this
section on mesial view. This slope forces the cephalic pole to a plane more
ventral than that of the inferior i)ole (figure 4). While the mesial and dorsal
surfaces show depressions, the lateral surface from dorsal view (figure 3)
shows a marked lateral bulging which gradually rounds into the superior
i:ole. Ventral to this lateral projection, seen from dorsal view, the nuclear
material is hollowed out in a mesial depression on the lateral surface. The
ventral surface, mesial to this de])ression, is well rounded into a mass which
shows a marked inferior shoulder from which tlie surface slopes concavely
into the cephalic i)ole. This may be S(>en in figure 4. This concavity
necessarily pushes the sujx'rior i)ole dorsally, so that it lies dorsal to the
mid-axis of the nucleus. The superior ])()le is a gi'adual convexity when
The Lower Portion of the Human Brain-Stem. 41
inspected from the ventral surface, while from mesial view it shows as a
shar]:) anp;le due to the great ventral concavity and slight dorsal convexity
causing it. The caudal jiole is placed dorsally and laterally to the mid-axis of
the nucleus. It is formed by the surfaces approximating in gentle convexities l)clow the margin of dorsal and mesial projection. It is a rounded
extremity, lying in close relation to the mesial vestiliular nucleus. When
viewed mesially (figure 4) the dorsal border of the nucleus forms a fairly
straight line, somewhat notched by the lower extremity of the nucleus
intercalatus. The ventral surface shows a marked convexity and bulging
in its caudal portion, the cephalic portion remaining comparatively straight
until the final concavity is begun.
All of the surfaces of the nucleus are, in genei'al, rounded so that there
are no margins between these faces. The irregularities and characteristics
of the oval nuclear mass have already been pointed out and need no further
description. The factors which seem to play the greatest part in modif\'ing
the true oval character of the nucleus are the superior portion of the luicleus
intercalatus and the peculiar looping of the seventh nerve.
NUCLEUS NERVI FACIALIS.
The nucleus of the facial nerve, lying in the lateral de])ths of the formatio
reticularis at about the level of the caudal end of the nuclei pontis, is shown
in the mesial view of the model (figure 4). It also appears on cross-section
in figure 13. The caudal end of the nucleus lies on a level with the most
cephalic portion of the nucleus ambiguus. The cephalic pole of this nucleus
corresponds in position to the similar jiole of the nucleus ncrvi abducentis.
In its cephalo-caudal diameter tlie nucleus measures 4.7 millimeters; in its
greatest transverse diameter, 2.8 millimeters; and in its greatest dorsoventral diameter, 4.1 millimeters.
The relations of the nucleus to other nuclear masses vary in the several
portions of the nucleus. The substantia gelatinosa lies dorso-lateral to this
nucleus nervi facialis (figure 13). Lateral and somewhat ventral to its
caudal half is found the scattered nuclear material comjjrising the corpus
ponto-bulbare. Ventro-mesial to its cei)halic two-thirds lies the nucleus
olivaris superior, in very close relationshij) throughout. The other relations
of the nucleus are wholly concerned with the formatio reticularis.
Essick (1912) has described the nucleus of the facial nerve as being
a pear-shaped cell-mass. With his description of the nucleus in the embryo,
this reconstruction of the adult nucleus agrees. In general, the nucleus
may be said to be a rounded mass which tapers gradually c(>phalatl after
a sudden constriction in its transverse and antero-posterior diameters (figure 4). Beginning caudally in a rather shar]) pole, the nucleus increases very
rapidly in all diameters, but especially in the dorso-mesial direction. This
more rapid increase in the oblique diameter cau.ses the luicleus to assume
an approximately oval shape soon after its caudal origin. The surfaces arc
42 A Reconstruction of the Nuclear Masses in
well rounded and pass into one another insensibly as soon as the great
increase in nuclear dimensions is attained. Slightly above the caudal pole
a slight concavity is made out on its ventral surface, and this is merged
cephalad with a slight ridge which sweeps from the middle of the ventral
surface laterally and cephalad. This ridge is continued superiorly as a
definite ventro-lateral projection of the nucleus, until it merges in the superior
pole. Just inferior to this ridge in the caudal half of the nucleus is a deep
depression on the lateral surface. Mesial to this ridge the nucleus is flattened
into a ventro-mesial surface, along which course the cell-columns of the
superior olive. Mesially, this surface insensibly blends with the mesial
curving face. Two marked longitudinal fissures occur in the dorsal convexity of the nucleus. These begin slightly above the caudal pole and run
as fairly deep furrows, becoming more superficial as they reach more cephalic
regions (figure 4).
Just cephalic to the middle of the nucleus all of these rounded surfaces
suddenly constrict to a considerable extent. From this point upward, the
nucleus, much narrowed in the two horizontal diameters, gradually tapers
to its sharp .sui)erior pole. This rounded caudal dilatation, with a constriction about the middle, passing into a tapering superior extremity gives the
whole nucleus the appearance of a pear.
The description just given applies to the nucleus on the left side of this
adult medulla. Although the nucleus on the right of this brain-stem was not
modeled, it was studied with the view of comparing its superior termination
with that on the left. The cell-mass on the left side, as modeled, shows
quite rapid tapering of the cephalic pole of the nucleus as compared with the
right. On the right, the characteristic motor cells and ground substance,
comprising the nucleus nervi facialis, extend cephalad as a tliin column to
a much higher level than on the left. This would tend to make the right
nucleus possess a much longer "neck" than the left and probably to be even
more pear-shaped.
Attempts were made to separate the nuclear mass of the seventh nerve
into the various component cell-masses, described as occurring in this nucleus
by Van Gehuchten and Marinesco. While undoubtedly such divisions of
the nucleus into component parts do exist in the human medulla, the modeling of these from the arbitrary outlines which were necessarily made to
determine the cell grouping was impossible. However, the occurrence of
the fissures and the ridge on the external surface of the nucleus is indicative
of such a division of the nucleus.
NUCLEUS NERVI TRIGEMINI.
The nucleus of the nervus trigeminus has not been modeled in its
entirety, as the model at its caudal cml still po.ssesses substantia gelatinosa
(figure 8), while at its cephalic end the main nuclear comjjlex is just developing (figure 14). Tliis descrii^tion, then, of the morphology of the nuclear
The Lower Portion of the Human Brain-Stem. 43
complex pertaining to the fifth nerve is necessarily incomplete, but it is
included for the purpose of describing as much of the complex as exists in the
model. The course and morphology of the substantia gelatinosa is practicall}'
complete in the extent of the model, and its description and relations should
have value.
The substantia gelatinosa Rolandi is that long nuclear mass, extending
from the upper cervical cord to the middle of the pons, which accompanies
the pars descendens of the nervus trigeminus. It possesses a characteristic
histology and is easily outlined in the medulla, but as it approaches the
motor nucleus of the fifth nerve it is cut off by many fibers and is with
difficulty delimited without the introduction of the individual element. The
nucleus will be described as extending cephalad from the caudal portion of
the model. Its relations to neighboring masses of gray matter will be
considered. In general, the pars descendens of the fifth nerve lies directly
lateral to it.
At the caudal extremity of the model, the substantia gelatinosa caps
the posterior column of the gray matter of this upper cervical cord. It is
a convoluted mass and fills the greater part of the column (figures 8 and 9).
In modeling, it was necessary to consider it as completely filling the column
a thing which it does very soon as one goes cejjhalad (figure 10). At the
caudal extremity of the model, then, the substantia gelatinosa practically
forms the oval posterior column which lies dorso-lateral to the central canal.
It possesses a smooth contour, as shown in figures 1, 2, and 3. The long
axis of the oval lies in an oblique plane, the lateral portion being dorsal to
the mesial extremity. The column extends slightly cephalad to the superior
termination of the decussatio pyramidum in a straight cephalo-caudal direction (figure 2). It widens from below upwards in this portion, as shown
in the same figure, a widening to be accoimted for both by the increased
size of the substantia and by the rotation of the long axis of the oval in a
dorso-ventral direction. This is shown in figure 9, where the long axis of
the larger oval has its dorsal extremity somewhat mesial to the ventral.
On the dorsal surface there occurs a slight eminence just above the
caudal ending of the nucleus fasciculi gracilis, as shown in figure 3. The
ventral surface is marked by a somewhat larger eminence in the middle of
the decussatio pyramidum (figure 1). As shown in iigure 3, the mesial
border extends cephalad and only very slightly laterally until the region
of the inferior end of the nucleus fasciculi cuneati is reached. It then is
pushed laterally (juite markedly and is overlaid by the projections of the
nucleus of Blumenau. The lateral margin of the substantia shows on dorsal
view a gradual lateral deflection.
Figure 2, the lateral view, shows the widened dilatation of the nucleus
just cephalic to the superior extremity of the decussation of the pjn-amids.
Sui^erior to this, the substantia diminishes slightly in size and shows a
gradually increasing tlorsal curving for a considerable distance. Its lateral
44 A Reconstruction of the Nuclear Masses in
surface is overlaid by the lateral plate of the nucleus of Blumenau already
described (figure 10). As this lateral plate recedes from its surface, the
substantia is characterized by a smooth notch on its ventral surface, followed
by a ventral projection toward the middle of the nucleus lateralis, and slightly
superior to these by a sharp dorsal spur. Figure 2 gives these markings.
The mesial surface throughout this extent is quite smooth and rounded.
The long axis of the oval still continues in the dorso-ventral direction. This
portion of the substantia, lying caudal to the cephalic pole of the nucleus
lateralis, shows but a slight lateral deflection. Just at the level of the
cephalic }3ole of the nucleus lateralis and mesial to the main ]:)ortion of the
nucleus ambigims, the substantia gelatinosa becomes quite thin, with the
maintenance of the dorso-ventral direction of the long axis (figure 11).
It takes a slight, rather abrui)t, mesial bend at this point, to be succeeded
quickly by a lateral deflection. These clianges in direction of the main
axis of the nucleus can be made out in flgure 4. From this point, cephalad
to its termination in the main sensor}^ dilatation of the nucleus, the substantia continues the dorso-lateral deviation of its cephalic course by a series
of slight mesial and lateral deflections similar to those just described.
Around the cephalic end of the nucleus tractus solitarii, the mesial
surface of the substantia gelatinosa jirojects dorsally and somewhat mesiall.y,
to join with the ventral surface of the nucleus nervi vestibuli medialis
(figures 4 and 12). Just superior to this dorsal projection there occurs a
circumscribed deeji depression, which is boimded ventrally by a rounded
edge. The substantia just cephalic to this is raised in a gradual but marked
mesial eminence. The oval of the substantia continues upward, bending
somewhat laterally as it passes the nucleus nervi facialis. In this region
the long axis of the oval becomes more oblique as its ventral edge is moved
laterally. Its dorsal margin joins with the nucleus nervi vestibuli superior
by large bridges of tissue (figure 13), which intermit in places. In the
region of the su]Derior portion of the nucleus of the seventh nerve the substantia gelatinosa becomes very irregular; it decreases in size and is broken
by many fiber bundles as they course through it in all directions. Continuing ventrally to the cephalic end of the nucleus nervi vestibuli superior,
it merges with a lateral sheet of cells which lies ventral to the most ventrolateral portion of the superior vestibular nucleus. The fusion of the sub-i
stantia gelatinosa with this lateral nucleus of the complex takes place at
the level of the superior pole of the seventh nucleus, slightly cephalad to
the caudal origin of the lateral sheet of cells. From this point cephalad
to the termination of the model, the nucleus may be described as a lateral
portion and the median motor portion, the nucleus motorius princeps nervi
trigemini.
When viewed from the lateral surface the nucleus of tlie fifth nerve
shows as an irregular mass placed between the ventral border of the superior
vestibular cell-mass and the dorsal jjorder of the lateral wall of the pontine
The Lower Puiiion of the Uiunun Braiu-Slcin. 45
nuclei. Its ventral border (figure 2), overlying laterally the dorsal terminations of the pontine wall, shows a curving with the convexity dorsal. The
superior border winds about the cephalic ventral angle of the superior
vestibular nucleus and then projects mesially along the straight ending of
the latter nucleus on the dorso-lateral plate. From the cephalic ventral
angle of the superior ^'estibular nucleus, to the termination of the model,
the lateral wall of the fifth nucleus is marked by an irregular lateral projection. This is due to the sudden widening out of the sensory reception
nucleus which caps the superior end of the substantia gelatinosa. The
expansion shows laterally (hgure 2) as a corrugated and notched projection
cephalic to the dorsal i>]n\v at the superior end of the vestibular nucleus,
and extends cephalad to the limit of the model. It is placed at first at some
distance laterally from the brachium conjunctivum, but it approaches the
ventral lateral margin of this very soon and sends a short dorsal spur around
its lateral and dorsal margin. This is shown at the extreme limit of the
model (figures 2 and 3). The lateral surface passes insensibly into the
smooth and extensive dorso-lateral plate of the nucleus, except at the cephalic
limit of the cell-mass, where the surface passes over the dorsal spur. The
dorsal-lateral plate (figure 3), underlying ventrally the brachium conjunctivum, is practically smooth throughout. Its mesial border is somewhat
irregular, but it shows caudally a rather rapid mesial curvature, which
becomes very mild in the cephalic portion of the model.
The ventral surface of the dorso-lateral plate is fairly smooth, and the
plate is much thicker transversely just cephalic to the upjjer limit of the
superior vestibular nucleus. This thickness reaches its maximum in the
lateral angle of the ventricle, where it exists as a marked rectangular ridge.
As one passes forward, the dorsal and ventral surfaces of this ridge approximate and the ridge merges into the thickened triangular plate. This
thickened triangular plate has its base in the caudal, thickened portion of
the dorso-lateral plate and extends cephalad, with its dorsal edge overlying
mesially the ventral surface of the dorso-lateral plate, to terminate by
ventral deflection in the column of the nucleus motorius princeps nervi
trigemini. The rectangular column is composed of large polygonal cells
closel}^ grouped together in its caudal extremity, but as it loses its character
cephalad these cells disappear from it.
From mesial view (figure 4) the chief motor nucleus of the fifth nerve
is seen to begin as a marked caudal spur which lies mesial to the cephalic
portion of the superior vestibular nucleus. This spur is composed of fairly
large cells. Traced cephalad the spur expands in the transverse diameter,
but especially in the dorso-ventral direction. This expansion occupies the
whole mesial surface of the nucleus as the superior vestibular nucleus terminates. It shows a wide, gentle, mesial prominence as the nucleus meets
with the lateral wall of the nuclei pontis, ventral to which prominence the
wall slopes laterally and ventrally. This prominence gradually subsides as
46 A Reconstruction of the Nuclear Masses in
it goes cephalad and this portion of the nucleus l^ecomes a thin sheet of
cells, overlying the fiber bundle which separates it from the dorso-lateral
plate. The surface is irregular, from the occurrence of small prominences
upon it. On its most cephalic portion in this model it shows several ventral
projections which overlie mesially the lateral pontine wall (figure 14).
Between the mesial eminence on this side and the rectangular column of
large cells (mesencephalic root) is a marked ridge lying just ventral to the
ventro-lateral angle of the fourth ventricle. It begins caudally as a small
column of cells in the indifferent gray matter at the angle of the ventricle
and continues cephalad to the limit of the model (figure 14). Its cephalic
course, in the extent of the model, is somewhat dorsal and mesial. The
mass expands as it goes cephalad into a mesial elevated ridge which becomes
greater in the mesial and dorsal projections. Soon after it arises caudally,
it is well marked off from the mesial cell-mass of the nucleus, but its dorsal
limit is not well defined until after the triangular plate, ventral to the
dorso-lateral roof plate, has joined with it. Histologically the mass is well
differentiated.
NUCLEUS INTERCALATUS.
With its caudal extremity at the dorsal angle of the nucleus nervi
hypoglossi and with its cephalic termination just cephalic to the inferior
limit of the- nucleus nervi abducentis, the nucleus intercalatus of Staderini
and Von Gchuchtcn extends superficially beneath the floor of the ventricle,
underlying the area plumiformis (figure 3). The nucleus measures in its
cephalo-caudal axis 8.3 millimeters and its greatest transverse diameter
measures 2.3 millimeters. Corresponding measurements given by Streeter
are 11 millimeters and 2.0 millimeters. Hence, in the medulla sectioned by
Streeter the nucleus was longer and perhaps narrower than in the medulla
used for this reconstruction.
Dorsally, the nucleus intercalatus is covered solely by superficial neuroglia and by the ependyma of the ventricle, except in its cephalic portion
where the stria? medullares course across it. The caudal two-fifths of the
nucleus lie mesially in relation to the dorso-lateral surface of the nucleus
nervi hypoglossi and laterally to the nucleus ala? cinerea?. The mesial
relations of the cej)halic three-fifths of the nucleus are with the nucleus
funiculi teretis and with the raphe; the lateral relations of this portion of
the nucleus are with the nucleus nervi vestibularis medialis and with the
nucleus nervi abducentis in the most superior part. Ventrally, the nucleus
is covered by the formatio reticularis. Such, then, are the relations of the
nucleus intercalatus to the adjoining masses of nuclear material.
The dorsal view of the nucleus intercalatus (figure 3) and the mesial
view (figure 4) show the general morphology to be that of a diamond, or of
two cones with their bases approximated. The point of maximum diameter
occurs at about the junction of the caudal two-fifths with the cephalic
The Loivcr Portion of the Human Brain-Stem. 47
three-fifths. Above this the nucleus tapers grackially to its cephalic pole;
Avhile in the lower two-fifths the nucleus narrows to a very thin edge. The
caudal two-fifths of the nucleus present four surfaces for examination
dorsal, ventral, mesial, and lateral but the cephalic portion of the nucleus
is more or less rounded on transverse section, so that no distinct surfaces
are made out.
From observation of serial sections of the brain-stem, inspected in order
from the spinal cord upward, the nucleus intercalatus is first noticed caudally
as a thin cap over the dorso-lateral surface of the nucleus nervi hypoglossi.
This cap of cells gradually broadens, taking the place of the decreasing
hypoglossal nucleus mesially and widening somewhat laterally, to reach its
greatest transverse and dorso-ventral diameters at the level of the cephalic
termination of the nucleus of the twelfth nerve (figures 3 and 4). The
mesial surface of this caudal two-fifths of the nucleus, hence, faces mesially
and somewhat ventrally as it conforms to the dorso-lateral face of the
hypoglossal nucleus. The surface is a smooth plane, narrowing in its upper
portion, although still showing dorsally to the motor nucleus but terminating
very quickly to pass into the cone-like upper three-fifths. The wide caudal
beginning of the nucleus intercalatus gives to this mesial caudal surface a
triangular aspect.
The dorsal view (figure 3) of the nucleus in its caudal two-fifths shows
also this triangular appearance with the apex downward. The mesial dorsal
angle of the nucleus is about 110, sharply defined and fairly straight. The
lateral dorsal edge, however, shows considerable curving, with the convexity
lateralwards, as the nucleus widens with the ventral dipping of the nucleus
alae cinerefe. This convexity gradually slopes into the upper core of the
nucleus. The dorsal surface of the lower two-fifths of the nucleus is fairly
smooth, with a gentle dorsal convexity. Two poorly defined and shallow
ventral depressions occur on its surface.
Ventrally, the surface of the nucleus intercalatus is also smooth, with a
slight ventral convexity. The mesial ventral border of this nucleus exhibits
a marked lateral convexity in its lower portion, followed above by a mesial
curvature. The lateral ventral border is fairly straight and runs almost
exactly in the cephalo-caudal axis.
A rectangle is formed by the lateral surface of the nucleus. This face
is not so smooth as are the other three surfaces in the caudal two-fifths of
the nucleus; two mesial concavities mark this surface, between which occurs
a fairly prominent ridge.
The arbitrary division for description of the nucleus intercalatus is
marked by a slight transverse ridge on the dorsal and mesial surfaces, and
by an elevation at the cephalic end of the ventro-lateral angle. Above
this the nucleus forms a gradually tapering truncated cone, as seen in
figures 3 and 12. The mesial surface shows a marked lateral bowing to
accommodate for the nucleus funiculi teretis (figure 12); the border turns
48 .4 Reconstruction of the Nuclear Musses in
abrujitly laterally at the caudal end of the nucleus of the round bundle and
then gradually cephalad to the cejihalic pole of the nucleus intercalatus.
The borders of the U[iper three-fifths of the nucleus intercalatus are fairly
straight and gradually converge, to form an abrupt cephalic pole, mesial
and slightly cephalic to the caudal extremity of the nucleus nervi abducentis
(figure 3).
The relative dorso-ventral and transverse diameters of the upper cone
of the nucleus and of the region of greatest thickness may be made out by
comparison of the dorsal and mesial views (figures 3 and 4). The two
diameters in these portions of the nucleus intercalatus are approximately
equal. Below the area of greatest dimensions, the dorso-ventral diameter
remains })ractically constant, while the transverse diameter diminishes rapidly
as one passes caudally.
NUCLEUS TRACTUS SOLITARII.
In this reconstruction of the adult medulla, the nucleus lying lateral
to the fibers of the tractus solitarius was modeled. Melius (1903) described
this nucleus in the medulla of the dog and identified a similar chain of cells
lying lateral to the tractus in the human medulla. It was considered that
this cell-column probably more truly rei)rcsented the nucleus of the solitary
bundle than do the irregular and ill-defined cell-groups situated mesially to
the tractus, between it and the nucleus alse cinereae. The dorso-mesial cellmass has been included by several authors as an integral part of the nucleus
of the solitary bundle; one portion of this dorso-mesial cell-collection has
been described in the subdivision of this study dealing with the nucleus ahe
cinerese.
The caudal end of this continuous chain of cells lateral to the tractus
solitarius lies at a slightly higher level than does the caudal enil of the nucleus
ate cinerccC (figure 10). The nucleus ends above just caudal to tlie superior
termination of the nucleus ahe cinerese (figure 4). Its cephalo-caudal length
is 10.1 millimeters, just slightly less than that of the nucleus alse cinereae.
Along the mesial and dorso-mesial border of the nucleus runs the tractus
solitarius. Dorsal to the nucleus is the nucleus fasciculi gracilis in the caudal
half, while in the cephalic half the nucleus nervi vestibuli pars descendens
occupies this position (figure 11). Lateral to the nucleus is the nucleus
fasciculi cuneati and in the most cephalic portion the substantia gelatinosa.
Dorsal to the nucleus lies the nucleus alse cinerea?, while mesial to it lies the
nucleus nervi hy])Oglossi. Ventrally and laterally from the nucleus of the
tract is found tlie substantia gelatinosa. At no point is the nucleus at all
superficially placed as regards the floor of the ventricle.
The nucleus begins below as an irregular column of cells, and runs from
tliis point ('(>phalad, somewhat ventrally and laterally. The caudal threefifths of the nucleus form an irregular cell-column, almost round on crosssection and situated at some distance mesially to the curving ventro-mesial
The Lower Portion of the HunKin Brain-Stem. 49
aspect of the nuclei fasciculorum gracilis et cuneati. In the upper twofifths of the nucleus the cell-column becomes flattened, so that the long axis
lies in the dorso-ventral i)lane. Al)out the middle of the nucleus there
occurs a well-marked, narrow, ventral spur; just cephalic to this are two
smaller and less well-marked dorso-mesial spurs. At the level of the more
cephalic of these spurs a marked dorsal concavity occurs on the ventral
border, compensated b}^ a corresponding dorsal convexity. Cephalic to
the curving resulting from that concavity and convexity, the nucleus resumes
its straight course. From mesial view the cei)halic half of the nucleus
appears much larger than the caudal portion. This appearance is due only
in part to the flattening above recorded, but there is an actual increase in
the cross-section of the nuclear material. The mesial surface of this cephalic
half of the nucleus is rendered irregular and rough by slight depressions
and ridges. Just before its cephalic termination, at a point where the nucleus
vestibularis medialis and the substantia gelatinosa come into contact, the
nucleus of the tractus solitarius exhibits an abrupt dorsal shoulder which
rounds out into the cephalic pole. This dorsal beak-like projection lies just
lateral and cephalic to a ventral projection from the nucleus ahe cinerete. The
lateral surface of the ujjper two-fifths of the nucleus conforms to the curve
of the mesial surface of the nucleus of the fasciculus cuneatus.
NUCLEUS OF ROLLER.
The nucleus, described by Roller (1881) as a "small-cell hypoglossal
nucleus," has been modeled in this reconstruction. It lies in the superior
dorsal depression on the ventral surface of the nucleus nervi h^vpoglossi
(figure 4). In its long cephalo-caudal diameter it measures 3.3 millimeters
and has an average transverse diameter of 0.8 millimeter.
Roller described the nucleus as lying about in the middle extent of the
hypoglossal nucleus. As seen from mesial view (figure 4), the nucleus lies
ventral to the cephalic one-third of this nucleus of the twelfth nerve instead
of in its middle region. It does lie, however, in the middle of the complex
of nuclei nervi hypoglossi et intercalatus. The nucleus is composed of much
smaller nerve-cells than those found in the hypoglossal and is separated from
the nucleus by transversely coursing fibers (figure 11).
The nucleus may be described as a round column of cells presenting
some slight surface irregularities. Its dorsal surface is cur\ed to conform
with the ventral surface of the hypoglossal nucleus, but on mesial view the
ventral border shows an independent form (figure 4). Beginning caudally
in the very sharp pole, the ventral border runs directly cei)halad for a short
distance and then turns in a sharp bend into a straight border running
cephalad and dorsally to the upi^er pole, which is tapering and sharp. The
nuclear mass widens and broadens quickly from its sharp caudal pole and
continues as a rounded column for two-thirds of its length. Cephalic to
this it tapers into its superior pole. The dorso-ventral and transverse
50 A Reconstruction of the Nuclear Masses in
diameters are in the main equal, except in its middle portion, where the
dorso-ventral diameter exceeds the other. This is coincident with a lateral
depression on the mesial face a depression pitted with small holes in the
nuclear material.
From ventral and lateral inspection, the convex lateral border of the
nucleus is made out. This margin shows a gentle curving throughout its
extent, the convexity of the curve being directed laterally. The greatest
lateral deflection of this border occurs at a level corresponding to the angle
in the ventral border; cephalic to this deflection the curvature is very gentle.
NUCLEUS FUNICULI TERETIS.
Considerable variation in the extent of the nucleus funiculi teretis is
found in different human medulUr. While the histological i)icture afforded
by this nucleus is similar in all brain-stems, the differences in the cephalocaudal dimensions and in the transverse diameter in several specimens are
marked. Streeter, in his diagram of the relations of the underlying nuclei
to the floor of the fourth ventricle, gives the nucleus funiculi teretis as
extending from the superior pole of the hypoglossal nucleus to the superior
pole of the nucleus intercalatus in other words, occupying as a continuous
column of cells the whole of the superior three-fifths of the nucleus intercalatus. In the adult medulla used for this reconstruction, two distinct
and unconnected typical masses of cells are made out as comprising the
nucleus funiculi teretis. The caudal mass of cells lies mesial to the cei:)halic
portion of the nucleus nervi hypoglossi. It is a very small mass of cells,
running through only a few sections, and is not included in this model
because of technical difficulties. The larger cell-column has been reconstructed and shows in figures 3 and 4.
The nucleus lies superficially beneath its eminence on the floor of the
fourth ventricle, just lateral to its mid-line. Laterally, it is in relation to the
nucleus intercalatus; mesially, to the mid-line of the ventricle (figiu'e 12).
Ventrally, it shows an intimate relationshij) to the formatio reticularis.
As modeled, the nucleus apj^ears as a short column of cells with rounded
margins and a larger caudal portion which slopes into the smaller cephalic
part. In cross-section, the nucleus shows as a triangle with convex siu'faces
and rounded edges (figure 12). When viewed dorsally (figure 3) it exhibits
almost a constant trans^'erse diameter throughout its extent with a fairly
straight and flat lateral surface and a rounded dorsal face which curves
rapidly into the mesial surface, as is seen on cross-section. On mesial view
(figure 4), the cephalo-caudal dorsal border is markedly contrasted with the
sl()])ing, somewhat irregular v(>nlral line of the nucleus. The caudal border,
on mesial view, is wide and turns abru])tly into the ventral margin, wliich
slopes irregularly to the tapering upper jiole. This ventral margin shows a
slight dorsal notch, cephalic to which the borders run less markedly dorsally.
The Lower Poiilon of the Human Brain-Stcni. 51
This gives rise to the broadened caudal half of the nucleus and a smaller
tapering superior portion. The upper pole is rounded and small. The
surfaces of the nucleus are all fairly smooth and regularly sloping into each
other. The ventral surface shows an irregularity coincident with the dorsal
angle in the ventral margin. It is flatter and less rounded than the mesial
and dorsal surfaces.
NUCLEUS LATERALIS.
Inserted in the formatio reticularis of the medulla between the substantia gelatinosa of the nervus trigeminus and the inferior olivary nucleus
is the column of cells known as the nucleus lateralis (figure 11). Beginning
caudally at the level of the third dorsal transverse sulcus of the olive (a
point midway between the inferior end of the dorsal accessory olive and the
caudal pole of the inferior olivary bod}') , this lateral nucleus extends cephalad
to the superior limit of the dorsal accessory olive. Dorsal to the nucleus
is the substantia gelatinosa; ventral to it is the dorsal leaf of the olive. Its
mesial edge is parallel in part to the lateral border of the dorsal olive.
Laterally the nucleus is in relation to the corpus restiforme.
These, then, are the relations of this nucleus lateralis to the other
nuclear masses about it in the medulla. The mori:)hology of this nucleus,
as reconstructed from the adult medulla, concerns a distinct and continuous
column of cells, well differentiated from the formatio reticularis in whose
lateral and ventral angle it lies (figures 2 and 4). At its caudal end the
nucleus is small, but as it continues cephalad a gradual increase in size
occurs, the nucleus reaching its maximum about the level of the middle of
the dorsal accessory olive. Just below this level the nucleus sends out a
distinct lateral spur which curves slightly ventrally to conform to the curvature of the olive. While in the main the nucleus maintains a fairly straight
course, it does show slight deflections from its main axis. One such deviation
occurs just abo^c its caudal end, the axis here turning ventrall}' after a short
dorsal ascent. Five processes project angularly to the dorsal side from the
main column of the nucleus, the most cephalic of these occurring just below
the cephalic end of the cell-column, two occurring in the area of greatest
cross-section, the other two being more caudally situated. Just caudal to
the cephalic end is a prominent ventral spur, below which the nucleus widens
after taking a slight curving direction, the convexity being dorsal. In the
part of greatest cross area, the lateral surface is marked by deep notches.
From the main cell-mass, several mesial projections occur; these have practically all a slight dorsal deflection. Two of these, in the caudal one- third
of the nucleus, are especially well marked.
In the lower half of the nucleus the transverse and dorso-ventral
diameters are about equal, but in the cephalic jiortion of this nuclear column
the antero-posterior diameter is in excess of the transverse. The conflgiu'ations of the nucleus are wellshown in figure 2,
52 A Recondnailon. of the Nuclear Masses in
NUCLEUS INCERTUS.
Following Streeter, the indefinite nuclear mass, placed directly beneath
the floor of the fourth ventricle in the prominence which runs toward the
aqueduct of Sylvius from the eminent ia abducentis, has been modeled as
the nucleus incertus. It extends from its caudal limit at the middle of the
nucleus nervi abducentis (figure 13) cephalad beyond the superior limits of
this model (figure 14). Streeter diagrams it as beginning dorsally in the
region of the knee of the facial nerve and extending cephalad with a lateral
convexity.
Mesial to the nucleus is the raphe and mid-line of the pons; ventral to
it occurs the formatio reticularis with also the nucleus reticularis tegmenti
pontis (figure 4). Ventral to its most caudal extremity is the cephalic half
of the nucleus nervi abducentis (figure 3). Lateral to the nucleus is the
cephalic portion of the nucleus vestibularis and the nucleus nervi trigemini.
Dorsal to the nucleus is the floor of the fourth ventricle.
In general, the nucleus may be said to be long and flat with a somewhat
wider caudal extremity. Its limits are very poorly defined in cross-sections
and it is felt that the terminations given this nucleus are subject to more
individual variation than are those of any other nucleus modeled. The
nucleus lies beneath the ventricular floor and constitutes in whole or in part
the flattened nuclear material seen there. This gray matter is rich in a
fine fibrillar network and in its midst there is diff'erentiated, in part, the
nuclear material as modeled. The nucleus may be said to present for
examination only two surfaces, the dorsal and ventral, uniting with each
other at the lateral and mesial borders.
As shown in figure 3, the nucleus begins abruptly in its caudal part but
soon widens and presents a convex smooth surface dorsally. The mesial
border is at first (juite close to the mid-line of the ventricle, but after a short
distance, in which a parallel relation is maintained, it curves laterally around
the fovea mediana. After this lateral deflection, the mesial surface continues
cephalad as an irregularly notched border which in general parallels the
mid-line, although it gradually l^ecomes more remote from it. This mesial
curve corresponds in general outline to that gi\'en by Streeter in his diagram
of the floor of the fourth ventricle. Th(> lateral border of the nucleus is shown
in part in figure 3. Beginning at the caudal extremity of the model, the
border i)ursues at first a straight, oblique direction ce]ihalad and laterally.
Then it i)arallels the mid-line for a distance, forming the narrowetl cephalic
portion of the nucleus. As the nucleus narrows, this lateral margin curves
toward the mid-line in a mesial convexity (o form a notch in the narrowest
part of the nucleus (figure 3). From this area cephalad, the nucleus widens
somewhat and then narrows as it ai)i)r()aches the sujxM-ior limit of the model.
In accord with this, the lateral margin shows a gradual lateral convexity
situated vcntrally to the mesencephalic portion of the fifth nucleus.
The Lower Portion of the Human Brnin-Steni. 53
The ventral surface of the nucleus is straight and smooth, excei)t about
the sixth nucleus. In this area the nucleus incertus exhibits a dorsal concavity with a ventral jirojection along the mesial surface of the nucleus
nervi abducentis. This elevation vanishes as the cephalic portion of the
sixth nucleus is reached, and cephalic to this the nucleus maintains its
smooth and flat form.
The relative diameters of the transverse and dorso-ventral portions of
the nucleus can be made out by comparison of figures 3 and 4. The dorsoventral diameter, as is shown, is practically constant throughout the extent
of the nucleus, while marked difference exists in the transverse.
NUCLEUS OLIVARIS INFERIOR.
From the caudal limit at a point in the basilar portion of the medulla
5.6 millimeters above the cephalic limit of the decussation of the pyramids,
the nucleus olivaris inferior extends cephalad to the joons. The cephalocaudal diameter of this nuclear mass measures 14 millimeters; the dorsoventral, 4.3 millimeters; and the transverse, 6.7 millimeters. With the
exception of the long cephalo-caudal diameter, the measurements given are
those derived by taking the averages of a series of measurements. The
transverse axis, if this term be used to designate the locus of the middle
points of lines drawn from the dorsal to the ventral surfaces of the olivary
leaves, varies in its relation to the antero-posterior ])lane of the raphe. In
the lower one-third of the olive this transverse axis forms approximately^
a 90 angle with the raphe. This angle becomes increased in the more
cephalic portions of the olive, being about 110 in its middle one-third and
reaching in the most cephalic portions an angle of 135 a])proximately (figure 6). With this increase in the angle formed by the transverse axes of the
olive with the raphe, the whole olive presents the appearance of having had
its cephalic portion rotated laterally while the inferior or caudal end has
been held in the transverse, right-angle position.
The volume of the olive, as determined by the displacement of water
by its model with later computation from the volume displaced, is 0.14 cubic
centimeter of nuclear material.
The general form of the inferior olivary nucleus is, as designated b}'
Miss Sabin, that of a "hollow shell with a wrinkled wall." This js shown
in the separate drawings of the olive (figures 5, 6, and 7) and in the lateral,
ventral, and mesial views of the whole model (figures 1, 2, and 4). The
nucleus presents for examination dorsal, lateral, ventral, mesial, cephalic,
and caudal surfaces. The so-called dorsal surface is actually directed i)osteriorly only in the lower one-third of the nucleus, for it assumes a marked
dorso-lateral deflection in its cephalic jwrtion, with the increased angle which
the transverse axis makes with the raphe in this suinn-ior jwrtion. Ihilike
the olive in Miss Sabin's reconstruction, the dorsal surface does not pass
54 A Reconstruction of the Nuclear Masses in
gradually into the lateral surface except in the cephalic portions, but it is
rather sharply distinguished from the lateral surface. The dorsal surface
is fairly straight, whereas the lateral surface shows a marked general convexity. On the ventral surface, the lower two-thirds are mainly flat, but
the upper one-third exhibits a slope toward the dorsal surface. The mesial
surface includes the hilum of the nuclear body and shows the invaginations
of the convolutions of the dorsal surface.
The convolutions of the olive resemble, in general, those of the cerebral
cortex as pointed out by Dr. Sabin. However, there is a very striking
difference between the principal and secondary sulci here in the olive, a far
more marked distinction than exists over the cerebral cortex. Generally,
as in the new-born, the main furrows on the dorsal surface run transversely,
but on the lateral surface this direction is converted into an oblique one,
the sulci coursing somewhat laterally but chiefly ventrally and caudally
(figure 2). The ventral surface shows the radial distribution of sulci as
pointed out by Miss Sabin (figures 1 and 5).
Three principal sulci, corresponding to those in the medulla of the newborn, are distinguished on the dorsal surface of the inferior olive (figure 7).
In the main, these are deejicr and run more closely to the l)order of the
hilum than do the other secondary furrows. These sulci tlivide the dorsal
surface into four lobes a cephalic lobe, occupying nearly one-third of the
whole dorsal leaf; two middle lobes (the second and third lobes of Sabin),
and the small caudal lobe. The first fissure, that between the cephalic and
the second lobes, is the most poorly differentiated of the main sulci (figure
7, a). Its importance, however, is assured by its broad character and the
general straight course which it follows, unaffected by the secondary sulci
which enter it. This first fissure begins just lateral to the border of the
hilum, courses out in a direct transverse line to almost the lateral limit of
the dorsal surface, and then dips laterally, caudall}^ and \-entrally as the
main oblique fissure on the lateral surface of the olive (figures 5 and 7, a).
The transverse dorsal portion of this main fissure is bisected by a very deep
furrow, arising just cei)halad to this first fissure a fourth ])riiicii)al fissure.
This deej) furrow bisecting the transverse is continued caudally as the deepest
fissure of this surface, forming the lateral margins of the second fissure and
of the middle lobes. This deep fissure runs almost exactly cephalo-caudally
with but slight lateral deviation in its caudal portion. Becoming more
shallow about the middle of the third lobe, it curves ovor ui)on the lateral
surface, to form the inferior limit of the middle lateral lobe. The second
chief transverse fissure of the dorsal surface arises from the dorsal edge of
the hilum at approximately its middle point and courses transversely to
the deep cephalo-caudal fissure (figure 7, 6). Its direction is transverse for
three-fifths of its length and then becomes caudally inclined, to fuse with the
cephalo-caudal fissure at an angle of 45. This second pi'incipal sulcus is
the deepest uf the fissures of the olive. The thin! or caudal principal sulcus
The Lower Porfioti of the Human Brain-Stem. 55
arises from the border of the hilum and may be divided into three equal
parts for description (figure 7, c). Tlie first portion is deej) and broadens
out somewhat as it courses laterally. This portion runs directly transversely,
to meet with a fairly deep cephalo-caudal secondary sulcus descending
from the third lobe. The main fissure then turns somewhat caudally as a
deep and very narrow sulcus (the second portion), which ends as a short but
deep cephalo-caudal secondary sulcus fuses with it, and the two continue
into the third portion, running cephalo-caudally with considerable lateral
deflection. It continues around to the lateral surface to form the inferior
limit of the third or caudal lateral lobe.
These, then, form the foiu- iirincii)al sulci of the dorsal surface of the
olive. Unlike the sulci described by Miss Sabin, all of these are continued
upon the lateral surface, either directly, as in the case of the cephalic and
caudal sulci, or indirectly through the agency of the deep cephalo-caudal
fissure as in the case of the middle transverse fissure. Whether or not this
deep cephalo-caudal fissure should be considered a principal sulcus is questionable. As seen in the view of this surface (figure 7) the middle transverse
sulcus {b) continues into it without interruption and it may be considered
as merely the lateral continuation of this principal fissure. But the cei^halic
part of the sulcus, extending caudally from above the first main transverse
fissure, argues strongly for its consideration as a principal furrow.
Five distinct lobes may be made out on the dorsal surface as shown in
figure 7. These may be considered as the four lobes described b}' Miss
Sabin, with the fifth lobe formed by the dorsal surface of the middle lateral
lobe. This fifth lobe lies lateral to the main cephalo-caudal fissure, bounded
above by the first transver.se fissure and medially and caudally by the fissure
to which it lies lateral. The other lobes lie in the regions marked off by
the transverse sulci.
The cephalic dorsal lobe is liy far the largest of the four, occupying
about one-third of the whole olivary nucleus and lying cephalic to the first
main fissure (figure 7, a). It is subdivided into a superior and inferior
portion by a rather shallow sulcus of the secondary order, which travels
parallel to the first main furrow. This transverse sulcus takes origin from
near the border of the hilum at a point midway between the origin of the first
main sulcus and the cephalic end of the hilum. It soon becomes somewhat
deeper and sends cephalad a short, broad furrow which contributes to the
formation of the gyri in the .superior half of the IoIm'. Continuing hiteralwards and becoming (juite sujjerficial, it sends caudally, in the middle part
of its course, a rather deep but short sulcus, which soon divides into two
portion.s a caudal projection, becoming superficial over the gyrus above
the first main fissures, and a mesial (more marked) furrow which extends
mesially toward the hilum and parallels the first main furrow. AV)(Mit these
sulci lie the gyri of the medial portion of the inferioi' half of the cephalic
lobe. The secondary transverse fissure, after giving off this caudal sulcus,
56 A Reconstrudion of the Nuclear Masses in
continues laterally as a somewhat convoluted furrow, giving off short, superficial sulci; and after deviating somewhat in a caudal direction, it ends by
becoming superficial over the lateral portion of the inferior half of the
cephalic lobe. Just above the caudal branch of the transverse secondary
fissure considered, but separated from it by a gyrus of the superior portion
of the cephalic lobe, is a shallow and short furrow, projecting cephalad and
laterally to end upon the most cephalic portion of the lobe. Just mesial to
the upper end of this short sulcus is a long and somewhat deeper furrow
which runs mesially in a straight line for some distance and then abruptly
turns caudally and again medially to end superficially at the upper end of
the hilum (figures 6 and 7). These constitute the fissures of the cephalic
dorsal lobe of the olive; the gyri are quite small in the upper half of the lobe,
while in the lower half two large gyri occur, in addition to several small
cephalo-caudal gyri. The most lateral gyrus of the inferior half overlies
the middle lateral lobe (figures 2, 5, and 7).
Caudal to the first main fissure (o) and cephalic to the second transverse fissure (b) lies the second dorsal lobe of the inferior olive (figure 7).
It is small, being limited on the mesial surface by the hilum, and on its
lateral aspect by the deep cephalo-caudal furrow. It consists of but one
main convolution, divided into rather narrow and short gyri which wind
between a caudal secondary fissure from the first main transverse sulcus
and two cephalic furrows from the second main fissure. In the main the
long axis of this lobe is exactly transverse, but laterally the lobe is continued
caudally in a narrowing sjiur lying between the cephalo-caudal and the
second transverse fissures. This spur dips increasingly deeply into the
furrow beneath the general plane of the dorsal surface until at its termination it lies in the dejiths of the furrows.
Limited by the hilum on the mesial side, bj' the second (6) and third
(c) transverse sulci cephalad and caudad respectively, and the inferior
I)ortion of the cej^halo-caudal fissure laterally, occurs the third dorsal lobe
(figure 7). In a similar sense this lobe also consists of one main convolution,
as in the new-born babe's medulla. But this convolution is marked by
many gyri which wind back and forth in a cephalo-caudal direction. The
general axis of this lobe lies transverse in the mesial one-third, but laterally
to this there occurs a caudal deflection of the whole convolution. The mesial
one-third of the lobe is marked off laterally by a caudal fissure, which arises
from the depths of the second transverse sulcus (6) and rapidl}' becomes
superficial, to vanish over the rather broad gyrus which projects caudally
as a peculiar spur into the third transverse fissure (c). Mesial to this caudal
fissure, there arise from the second transverse sulcus two rather sujierficial,
(caudally directed furrows, which aid in jjroducing the gyri of the superior
])art of the lobe. Lateral to the caudal fissure from the second transverse
sulcus is a small and superficial fuirow, directed caudally, just mesial to the
])()iiit of fusion of tlie cephalo-caudal and transverse sulci. From this
The Lower Pcniion of the Human Brain-Stem. 57
cephalo-caudal sulcus there arises a single caudally directed fissure, short
and superficial, separating off a gyrus of the lobe which lies upon the mesial
wall of the deep furrow. The portion of this lobe which lies between the
cephalo-caudal and third transverse sulci runs caudally and somewhat
laterally. This consists of one main convolution, broken into two parallel
gyri by a middle superficial sulcus which follows the general direction of the
convolution but has a gradual curve, the convexity being mesial. Laterally,
the lobe projects around to form the third or caudal lateral lobe (figure 2).
Caudal to the obliquely coursing third transverse sulcus (c) lies the
caudal lobe of the dorsal surface (figure 7). It is very small and does not
extend to the lateral surface. It consists of two main gyri, divided in their
mesial portion by a short transverse secondary sulcus, which arises at the
caudal end of the hilum. The more cephalic of the two gyri lies more
dorsal than the caudal gyrus in its mesial part, but laterally the two gyri
approach and fuse with one another to form a flat and wide lateral convolution. The caudal part of the gyrus is continued down as a small s]nir to
form the inferior pole of the olive.
Bounded superiorly by the lateral part of the first dorsal transverse
fissure (a), and mesially by the cephalo-caudal furrow, the lateral dorsal
lobe occurs (figure 7). Its main axis is ajiproximately cephalo-caudal. At
the upper mesial part of the lobe there is l)ut one convolution, but as this
goes laterally and caudall}', it is severed into the two main gyri of the lobe
by a fairly deep oblicjue sulcus which parallels the main cephalo-caudal
sulcus for some distance and then curves laterally and caudally to separate
the first and second convolutions of the middle lateral lobe. The gyrus
lying above this sulcus widens somewhat as it curves upon the lateral surface
and shows a shallow but broad groove upon it, becoming the superior convolution of the lateral middle lobe (figure 2). The gyrus lying mesial to
and inferior to the sulcus just described, continues inferiorly and slightly
laterally as a rather narrow convolution, then rapidly widens out and curves
over into the two lower gyri of the lateral middle lobe. The most inferior
part of this descending convolution is separated from the main mass by a
shallow curving sulcus, which ends as the lateral and dorsal surfaces meet.
Above this sulcus the beginning of a rather deep lateral fissure is seen, the
furrow which divides the convolution into the two lower gyri of the middle
lateral lobe. The most inferior portion of the gyrus is composed of the
caudal spur or lowest gyrus of the lateral middle lobe.
The lateral view of the olive (figure 2) suggests, more than any other,
the idea of a rotation of the superior pole of the olive. The slope of the main
axis of the olive, when viewed from the side, is dorsal in the cephalic region,
the mesial part of the cephalic lobe of the dorsal surface projecting far more
dorsally than the other two-thirds of the nucleus. The lateral portion of
this lobe is somewhat dorsal to the rest of the nuclear mass on lateral \iew,
a fact in accord with the obtuse angle maile l)y the transverse axis of the
58 A Reconstruction of the Nuclear Masses in
olive with the raphe in the cephahc part. Three lobes may be distinguished
on the lateral surface, the lateral continuations of the cephalic, lateral, and
third dorsal lobes. The main fissures separating these lobes can be made
out in their depths only when the olive is viewed from the inferior side as
the cephalic lobe overlies dorsally and laterally the first transverse sulcus
(a), while the lateral dorsal lobe similarly obscures the lateral projection of
the dorsal cephalo-caudal fissure.
All the fissures seen on the lateral view have a marked obliquity caudally
and ventrally (from above downwards and forwards) in the upper two-thirds
of this olivary mass (figure 2). In the lower one-third the sulci run transversely and then curve ventrally and cephalad. Xo secondarj' sulci at right
angles to the main furrows are made out on this surface, the secondary sulci
all being long and shallow, paralleling the direction of the main grooves.
The first main lateral fissure, a continuation of the first main dorsal furrow
(a), is concealed by the overlying gyrus of the lateral cephalic lobe for a
portion of its course. About the middle of the lateral surface the furrow
becomes superficial and may be traced ventrally and caudally to its ending
(figure 5, a). Just before its termination at the junction of the lateral and
ventral surfaces the .sulcus bonds abruptly cei)halad and ventrally. Sui)crior
to this main furrow is a rather long parallel groove which reall}^ follows the
line of the secondary transverse sulcus of the dorsal cephalic lobe, although
interrupted by a small gj'rus. Sujierior to this sulcus are several parallel
grooves, which divide this lateral cejihalic lobe into many obliquely coursing
gyri. Taken as a whole, the lateral cephalic lobe comi;)rising one-half of
this surface ma.y be considered as made up of three main convolutions, all
of which follow the course of a ventral and caudal projection.
The middle lateral lobe (figure 2) is likewise composed of three chief
convolutions, separated by well-marked sulci. The first groove, encountered
as on(! goes caudally from the lateral obliquity of the first transverse dorsal
sulcus (a), is a parallel and deep sulcus which arises from the lateral end of
the transverse furrow and runs caudally, laterally, and ventrally to terminate
in the first lateral sulcus as it bends cephalad. The small gyrus, thus
delimited by these two obliriue grooves, is concealed in its superior half ])y
the overhanging caudal gyrus of the lateral cephalic lobe. The inferior
part of this gyrus is readily seen from the lateral surface. Caudal to this
gyrus is the first main convolution of the middle lateral lobe a projecting,
flat, l)road gyrus which curves olilicjucly caudalwards, lateralwards, and
then ventralwards and cephalad. Shallow, broad, and somewhat indistinct
grooves mark its surface. It is bounded below by a fissure which is concealed on this view , tlic oblique sulcus of the lateral dorsal lobe. Caudally
are placed the other two convolutions of this lobe, separated by a shallow
crescentic fiUTow. The middle {'on\'olutioii projects laterally more than do
the other gyri, while the lower lobe is distiiiguislied l)y a caudal projection
The Loioer Portion of the Human Brain-Stem. 59
or small gyrus, poorly separated by a shallow, ill-defined groove. The
inferior convolution shows a marked crescentic outline, the concavity of
the crescent being directed cephalad. Interiorly, this middle lateral lobe is
bounded l)y the lateral termination of the dorsal cephalo-caudal sulcus; the
sulcus ends in the mid-line of the lateral surface, but its direction is continued
by a short curving groove, which leads cejjhalad and ventrally.
Inferiorly, there occurs the caudal lobe of the lateral surface (figure 2).
This is bounded in its cephalic part by the sulcus just mentioned as forming
the inferior limit of the middle lobe. Caudally the lobe is bounded by the
lateral superficial ending of the third transverse gyrus and by the polo of
the nucleus, which the lobe forms on this surface. The lobe itself is composed of a narrow gyrus on its dorsal side, a continuation of the dorsal third
lobe. Just caudal to the spur on the third convolution of the middle lobe,
the caudal lobe widens into a broad convolution, which curves ventrally and
cephalad into the ventral surface (figures 1 and 5). A single, shallow cephalocaudal fissure occurs on the ventral one-third of this lateral caudal lobe. The
whole caudal lobe comi)rises one-sixth to one-seventh of the lateral surface.
On direct ventral view (figure 5), the ventral leaf of the inferior olive
comprises but the lateral half of the field, while the ventral surface of the
dorsal leaf shows in the mesial portion. As described by Mi.ss Sabin in the
new-born, the course of the ventral fissures is radial, the central jwint being
slightly inferior to the middle of the ventral border of the hilum. Superior
to this point of radiation lies the ventral part of the cephalic dorsal lobe;
inferior to it the ventral prolongation of the middle lateral lobe and the
dorsal lateral lobe, while far caudalwards, forming the inferior limit of the
hilum, occurs the ventral part of the dorsal caudal lobe. The ventral aspect
is concerned with a marked ventral bulging of the middle part of its surface,
in the inferior i)ortion of the cephalic lobe and in the ventral part of the
middle lateral lobe. From this jirominence the ventral surface slopes
dorsally, both cephalad and caudad, but this slope is soon reduced to fairly
flat planes, which curve over into the cephalic and caudal surfaces. The
lateral outline, on ventral inspection, exhibits a marked lateral i)rominence
of the inferior portion of the cephalic lobe, overhanging, if such a term be
possible, the lateral middle lobe (figures 1 and 5). Caudal to this, the lateral
middle lobe develops a lateral ])rominence in its lower portions, overhanging
in turn the lateral caudal lobe, which differentiates itself sharply at a 90
angle from its cephalic neighbor; on the inferior extremity occurs the caudal
tip of the caudal dorsal lobe (figures 1, 5, and G).
From the center of radiation, which really forms the caudal ventral
portion of the cephalic lobe, the most striking fissure is that which arises
from the cephalic border of the center and passes cephalad in a fairly direct
cephalo-caudal direction, to end superficially on the cephalic surface of the
cephalic lobe (figures 1 and o). Between this furrow and the ventral border
60 A Reconstruction of the Nuclear Masses in
of the hilum are several short and shallow furrows, all of which pursue this
cephalo-caudal direction. The most cephalic of these courses as a deep
groove upon the cephalic pole of the olive, to turn medianly in the axis of
the cephalic one-third of the nucleus. Lateral to this prominent cephalocaudal groove, are three short and shallow sulci running in the same direction.
Still lateral to these short grooves occurs the rather deep fissure which marks
off laterally the most inferior gyrus of the cephalic lobe on the lateral surface.
This sulcus ends at some distance from the center of radiation. Caudal to
this occur the notch and suggestive oblique furrow formed by the superficial ending of the first transverse dorsal fissure (o), separating the cephalic
lobe from the ventral portion of the lateral middle lobe. From the middle
of the latter lobe there radiates a shallow groove, directed laterally, caudally,
and somewhat dorsally. Below this an interrupted shallow grooving {b)
marks the caudal ending of this middle lobe on the ventral surface. This
grooving actually continues around in the line of the second transverse
dorsal fissure. More caudally, the third lateral lobe presents its ventral
surface, cut into gyri by two small cephalo-caudal sulci and showing a marked
ventral prominence below. On the mesial side this lobe is separated from
the dorsal caudal lobe by a short cephalo-caudal furrow, occurring but
slightly lateral to the border of the hilum. This small caudal lobe appears
Y-shaj^ed on this view, the arms of the Y forming the limits of the hilum
inferiorly, while the stem forms the extreme caudal pole.
The cephalic surface of the inferior olive is not shown directly in any
of the plates, but a very good idea of its mor]ihology may be obtained from
the views of the other surfaces. It is rounded, forming the cephalic covering
of the olivary cavity. It is rather deeply grooved by the cephalic continuation of the ventral cephalo-caudal furrow mentioned above. Dorsal and
lateral to this deei)er furrow occur several superficial grooves, which divide
the surface into small gyri.
The caudal surface shows little not already described from the other
views. The main portion of this surface is occupied by the caudal lobe which
forms the lower limits of the olivary cavity. This lobe, as already mentioned,
gives origin to a caudal spur, showing in figures 5 and 6. The superficial
ending of the third dorsal transverse fissure (c) also shows on the caudal
surface of the inferior lateral lobe.
Mesially the hilum occupies the greater portion of the field, showing
about it an edge of nuclear material and within it the reverse of the convolutions, esijccially those on the dorsal surface (figure 6). The general
contour of the hilum, with its prominent dorsal border and its ventral border
retiring laterally, is very well shown in figure 6. Beginning at the cephalic
dorsal angle, the border of the hilum at first goes straight ventrally; it is
soon turned abrui)tly caudally by a caudal ])roj(>ction of the cephalic lobe;
then again turns ventrally and somewhat laterally to a small notch in the
The Lower Portion of the Hutiuui Bratii-Ston. 61
cephalic border. After an oblique caudal slope, the border turns straight
ventrally for some distance along- the edge of the prominent upper cei)halic
lobe, which is well seen on ventral view (figvu'e 5). This border ends abruptly
in a right angle at the level of the secondary transverse gyrus of the dorsal
cephalic lobe. From this i)oint the border of the hilum continues caudally
in three great curves. The first of these curves, convex dorsally, ends at
the level of the first main transverse fissure on the dorsal surface. The
border is thence continued in the second curve, convex ventrally, to the
level of the second main transverse dorsal fissure. The third curve, arising
at this point and showing its convexity ventrally, continues around to the
dorsal border, forming in its course the rounded caudal limit of the hilum.
The main line of the dorsal border of the hilum is straight, but it is broken
by the notches made at the origin of the second and third transverse fissures
on the dorsal side (figure 7).
The interior of the olive shows convolutions and sulci, which are in
every case merely the rcver.se of the sulci and gyri described on the oi:)posite
surfaces. The caudal end is formed by the caudal dorsal lobe and the third
lateral lobes, while the cephalic cap is composed wholly of the cephalic lobe.
The olive is, then, a "hollow shell with a wrinkled wall." The lobes
described on the various surfaces merge into one another so that they may
be considered as a cephalic lobe, occurring on all the surfaces; a second
dorsal lobe, small and only on the dorsal surface; a third dorsal lobe, extending from the dorsal border of the hilum around all the surfaces; a lateral
lobe, arising as the dorsal lateral lobe, forming the middle lobe on the lateral
surface and continuing over to the center of radiation; and the small caudal
lobe. Hence, we may add that the olivary nuclear mass is composed of
these five easily distinguished lobes, some of which extend around the whole
leaf, while others are small and limited in extent. The three main transverse dorsal fissures exist in the adult as in the new-born (Sabin), but there
is in addition a definite cephalo-caudal fissure which continues, in the characteristic caudal obliquity, the lateral projection of the second transverse
furrow. These sulci are continued to the point of radiation on the ventral
surface, either directly or by a shallow, ill-defined grooving.
The description given above is that of the left inferior olivary nucleus.
The right olive was likewise modeled, but with the purpose of showing its
relation to the formatio reticularis and to the other nuclear masses (figure 1,
cf. two sides). As it can not be removed from its position, an accurate
comparison with the left can not be made. However, it may be said that
although some slight differences may be made out, even as it lies in the model,
the same main fissures and furrows exist as in the left. There is the same
characteristic ventral radiation of furrows, the same distribution of lobes
on the lateral and ventral surfaces, with consequent agreement of all essential
morphological elements.
62 A Reconstruction of the Nuclear Masses in
NUMBER OF CELLS IN INFERIOR OLIVE.
In order to obtain an approximate idea of the number of cells in the
inferior olivary nucleus, calculations based on different methods were made.
All of the methods used had to do with the volume of the nuclear material
comprising the olive. This was determined, as already mentioned, by the
displacement of water by the model. This volume was determined as 460
cubic centimeters for the magnification of 15 diameters. From this, the
actual volume of the olive was found to be 0.14 cubic centimeter (460 cubic
centimeters divided by the cube of 15). To determine the number of cells
per cubic centimeter of nuclear material in the olive, counts were made of
the cells occurring in the olivary masses, as follows :
(1) The total number of cells occurring in the olive in one section were
determined by actual counting of all nuclei by means of traveling back and
forth with a mechanical stage. Then the area of the olivary convolutions
was obtained by means of a perimeter and the volume computed bj' multiplying the perimeter value by the thickness of the section (40/x). The volume
containing these cells was controlled by cutting out in wax the magnified
drawing of the olive in that section and determining the volume of the wax.
By this method the olive was found to contain 950,000 cells.
(2) The area of a high-power field of the microscope was determined
by measurement and the volume of the field comi;)uted by multiplying the
area by the thickness of the section. All the cells were then counted in a
number of fields and the average value used in the computation for the total
number of cells. By this method, which may be considered as fairly accurate
as soon as one learns to count accurately the cells in a field, the nuclei
in the olive were found to be 1,050,000. This value is an average of many
counts, the highest being 1,068,000 and the lowest 1,038,000 by this method.
(3) The third method used for determining the cells in the olive was
that of counting the cells occurring in a definite square projected into the
field of the microscope from squared centimeter paper by an Abbe camera
lucida. The exact size of this field could be determined readily by measuring
a ruled slide (0.1 millimeter) in terms of the centimeters on the squared paper.
The volume of this sciuare was then determined by multiplying the area by
the thickness of the section. Further computations were then made to
secure the number of cells in the total volume of the olive. By this method
the total number of nuclei in the olive was found to be slightly less than
1,100,000, and a value but slightly above that determined by counting the
total cells in the measured microscopic field. The nucleoli were also counted
by this method and found to be 530,000 in one inferior olivary nucleus.
Considering the second and third methods to be far more accurate than
the more laborious first method, it may be said that the total number of
nuclei (both of ganglion and neuroglia cells) in one inferior olive is between
1,000,000 and 1,]0(),()00; the number of nucleoli is about 500,000. These
counts were made in conjunction with Dr. fossick, to whom credit for the
methods used is gladly given.
The Lower Portion of the Huiium Brain-Stem. 63
NUCLEUS OLIVARIS ACCESSORIUS MEDIALIS.
Placed between the stratum interolivare and the inferior oHvary nucleus,
but separated from the latter by the fibers of the nervus hypoglossus, is
the nucleus olivaris accessorius medialis. This medial accessory olive is a
flattened irregular cell-mass, arising caudally considerably nearer to the
decussatio pyramidum than the inferior olive, but extending ce[jhalad to a
point somewhat caudal to the cephalic pole of the inferior olivary body
(figure 4). In cephalo-caudal extent, it practically equals that of the olive,
beginning and ending caudally to the corresponding points on the main
nucleus. As a broad, thin sheet of cells it covers almost completely the
hilum of the olive on the mesial side, although the cell-masses are lacking
somewhat along the dorsal border. The whole nuclear mass of this medial
accessory olive is shown in figure 4.
The nucleus olivaris accessorius medialis, on the left side of this adult
medulla, consists of a continuous flat and broad column of cells, presenting
two constrictions in the mass and also showing separated nuclear masses
at different portions of the whole extent. Beginning abruptly in the formatio
reticularis, the caudal portion of the main mass of the medial olive quickly
widens into the broadest ]iortion of the whole mass. The general direction
of this portion is obli(iucly lateral, making an angle of about 135 with the
raphe. With the broadest portion existing at the level of the inferior olivary
pole, this sheet of cells, convex medially, continues uj^ward to the level of
the third dorsal transverse fissure, where it exhiliits a marked constriction.
Just caudal to this constriction its dorsal border is continued posteriorly
into a well-marked projection lying entirely behind the general line of this
border. Undoubtedly this constriction corresponds to the division between
the caudal and middle cell-masses found by Sabin in the new-born, but
in the babe the degree of constriction is apparently far more marked.
Above this constriction the main cell-mass extends as a continuous, fairly
broad sheet to the level of the first dorsal transverse fissure. The ventral
border of this portion is slightly curved with the convexity dorsally. The
dorsal border, from the point of constriction, gradually and irregularly
projects more dorsally, until at the level of the second dorsal transverse
fissure it juts suddenly dorsally, to form the neck of an irregular cell-mass
(figure 4). This new cell-mass is almost square from mesial view, showing
a deep notch on its cephalic surface and separated from the main mass of
the mesial oli^'e by a still deeper notch. Its pedicle is rather broad, but is
perforated by a distinct band of fibers. The main nuclear mass, after an
abrupt ending of the principal broad column of cells at the level of the first
transverse fissure, is continued cephalad by a narrow mass of cells which
stretches dorsally and cephalad to widen above into an irregular cephalic
broadening. This broadened mass exhibits a dorsal i)rojection in its superior
half and a sharper, narrower ventral spur at its cephalic pole.
Such, then, is the main sheet of cells comprising the m(\sial accessory
olive. In the main, it shows the same primary divisions as found by Miss
64 A Reconstruction of the Nuclear Masses in
8abin in the new-born medulla, but it differs from her reconstruction in the
fact that the cephalic cell-mass is connected with the middle mass, and in
the fact that the constriction between the caudal and middle lobes is not as
marked in the adult as in the reconstruction of the new-born.
Dorsal to the caudo-dorsal portion of the inferior olivary nucleus, and
lateral and somewhat dorsal to the lower part of the main cell-mass of the
mesial accessory olive, is a short and small, regular column of cells, belonging
to the mesial accessory olive. This lies very closely related to the inferior
portion of the caudal lobe. It probably corresponds to the cell-collection
lying dorsal to the caudal column of cells as described by Miss Sabin. At
the dorsal border of the hilum, on a level with the secondary transverse
dorsal fissure and with the cephalic portion of the medial accessory olive,
is another cell-mass, rather shorter but broader and thicker than the one
described as lying dorsal to the caudal cell-mass. This mass undoubtedly
corresponds to the small collection of cells found dorsal to the superior column
in the new-born. Ventrally and somewhat laterally, the cephalic portion
of the main cell-mass in the adult is continued into two irregularly shaped
collections of cells, the lateral and larger of which lies behind the other on
mesial view. Just cephalic to the superior ventral angle of the middle cellmass of the mesial accessory olive there lies laterally a rather larger and quite
regular cell-mass, whose cells resemble those of the mesial olive and should
undoubtedly be considered as belonging to the same complex.
No cell-masses, corresponding to the two collections lying dorsal to the
middle column of cells in the new-born, were modeled in the adult (figure 4).
The two dorsal spurs, the inferior arising from the superior dorsal angle of
the caudal division and the superior from the middle of the dorsal border of
the middle division, may perhaps be the analogies of these two dorsal cellmasses. Such a view has considerable support in the great range of variations seen in the divisions of nuclear material efTected by the nerve fibers.
Lying along the middle three-fifths of the ventral border of the main
cell-sheet of the mesial accessory olive, is an irregular cell-column (figure 4) .
This column also lies ujion the pyramids. Histologically, there is more
correspondence to the structure of the arcuate nuclei than to the mesial
olive, but its relation to the mesial accessory complex may be assumed by
virtue of its position (figure 11). The caudal portion of this arcuate-olivary
column is attached to the cephalic portion of the caudal division of the main
cell-sheet, but no other connection with the mesial olive is made out. This
column shows a gradual dorsal prolongation just inferior to its middle portion
and a small but prominent ventro-lateral spur above its middle. It ends
just caudal to the cephalic ending of the middle division of the main cellmass, projecting somewhat mesially in its more superior part. This cellmass is easily made out in figure 1.
The right medial accessory olive, as modeled and fixed in position to
show constantly its relationships, shows, as far as can be made out, the same
The Lower Poiiion. of (he Hinudii Bnihi-Stem. 65
three divisions of the main nuclear sheet. The constriction, however,
between the caudal and middle lobes, is further accentuated by the presence
of a large fenestration in the cell-sheet, made by the coursing fiber bundles.
The cephalic division is not large nor well marked off, Init it follows, in the
main, the same general direction and relationship as does the corresponding
mass on the opposite side. Dorsal to the middle part of the middle division
is a somewhat larger dorsal projection than on the opposite side, but it has
very similar characters (figure 1). The caudal lobe at its cephalic dorsal
angle also has a spur corresponding closely to the spur on the opposite side.
Small nuclear masses occur just above this spur. These are not found on
the left side.
NUCLEUS OLIVARIS ACCESSORIUS DORSALIS.
The nucleus olivaris accessorius dorsalis sinister is a thin sheet of cells,
about one-third the length of the olive and slightly less than one-half its
transverse diameter. As a more or less rectangular plate, it overlies dorsally
the second and third dorsal lobes, and is represented in outline in figures 5,
6, and 7. It is shown in part in figure 4. Beginning caudally just cephalad
to the third transverse fissure (r) of the dorsal surface it rapidly widens to
its line of greatest transverse diameter over the second dorsal fissure (6)
and thence continues cephalad in a slightly narrowing body to an abrupt
ending over the first dorsal fissure. Its mesial l)order at the inferior end
lies slightly lateral to the dorsal border of the hilum, Init soon approaches
and corresponds to that border. Hence, the dorsal accessory olive lies over
the dorsal middle and mesial third of the main nuclear mass. Dorsally, it
is covered by the formatio reticularis. The surface of the dorsal accessor}^
olive is smooth, but it shows a slight convexity ventrally, the point of greatest
convexity being over the deep second dorsal transverse sulcus (6). The
right nucleus, as far as can be made out, corresponds fairly exactly to the
left. The nucleus has approximately the same extent as that in the newborn, as reconstructed by JNIiss Sabin.
THE PONTINE COMPLEX.
In this reconstruction, the nuclear material of the caudal portion of the
pons, of the nuclei arciformes, and of the corpus ponto-bulbare was modeled. The description of these structures will deal with these as portions
of a single morphological unit, as they are undoubtedly portions of the same
primary cell-mass. Essick (1912) has shown that the pontine miclei are
formed from cells migrating in the embryo from the Rautenlip|)e of His in
the lateral wall of the fourth ventricle, along the course of the corpus pontobulbare, which he first described in 1907. This, then, necessarily includes
the corpus ponto-bulbare in the pontine nuclei. Somewhat similarly the
arcuate nuclei are formed from cells which migrate superficially around the
surface of the medulla from the Rautenlippe. These arcuate nuclei are of
66 A Reconstruction of the Nuclear Masses in
the same histological structure as are the pontine nuclei, and at the lower end
of the pons the arcuate nuclear material insensibly passes into the pontine
masses. It is believed, from consideration of these factors, that any description of these nuclei should deal with the three nuclear masses as integral parts
of one main nuclear mass. This plan will be followed in the description, the
arcuate nuclei and the corpus ponto-bulbare being considered first, and then
the pontine nuclei as the cephalic portion of these integral parts.
Inspection of a number of brain-stems cut in serial sections will lead
to the conclusion that marked differences exist in the amount of nuclear
material comprised in the arcuate nucleus and in the corpus ponto-bulbare.
Some of the series will show great amounts of this gray matter scattered
along the course of the fibra? arciformes externtB ventrales with large redundant arcuate nuclei, while in other brain-stems the amount of these peripheral
cell-masses is meager and very small. With such marked diversity in the
extent of the nuclear material along the ventral surface of the medulla, each
reconstruction must be considered wholly from the standpoint of the presentation of the nuclear material in that particular brain-stem. Similar differences exist in the amount of the cellular material comprising the corpus
ponto-bulbare. The adult brain-stem, which has here been reconstructed,
is very poor in the nuclear matter comprising both of these cell-masses and
the resulting model of these two cell-columns must be taken as indicative
of the extent and course of the masses rather than as the morphological
form for every brain-stem. Similar differences, of course, exist in all nuclear
masses, but these differences are not in the main sufficient to change appreciably the morphology.
NUCLEI ARCIFORMES.
The nuclei arciformes in this reconstruction exhibit considerable differences on the two sides of the model, as can be seen from figure 1. Neither
of them is a continuous cell-mass, but both are interrupted about the middle
of their extent. Both begin at approximately the same level caudally, just
caudal to the inferior termination of the nucleus olivaris accessorius medialis.
Both finally terminate by merging with the pontine nuclei at the caudal
extremity of the pons, their extent being about coincident witli that of the
inferior olive.
The arcuate nucleus on the left side begins caudally as a flat, rather
thin sheet of cells, which is placed in the midst of the ventral external arcuate
fibers, ventral to the pyramids. With the smallest diameter dorso-ventral,
the column can be traced cephalad (figure 2) as a continuous cell-mass to
slightly superior to the point of radiation on the vcnti-al leaf of the olive.
In this extent of the lower continuous mass, the column shows a lateral
convexity, so that even the upper end of this first portion of tlic nucleus is
placed lateral to the inferior end. Two marked lateral notches are seen on
the mesial border in its convexity. Just caudal to the inferior of these
notches is a well-defined lateral projection (figure 1). A much smaller
The Lower Portion of (he Human Brain-Stem. 67
lateral projection shows a similar relation to the superior of the notches.
The caudal end of this portion is rounded and shows a widened transverse
portion, cejihalic to which the nucleus preserves almost intact its transverse
diameter. The cephalic end of this first portion of the left arcuate nucleus
inclines somewhat ventrally, as shown in figures 2 and 4. At the superior end
of this first portion, two small masses of nuclear material occur, separated
from each other and from the superior cell-column of filler biuidles. These,
with their long axes transverse, arc shown in figures 1, 2, and 4. They lie
cephalic, mesial, and slightly ventral to the cephalic pole of the first portion.
The superior of these lies more cephalic, mesial, and ventral than the inferior.
Cephalic to these small nuclear masses, the arcuate nucleus on the left again
becomes a continuous mass which runs to the pontine nuclei. As shown in
figure 1, the whole column shows a marked convexity toward the mid-line
and also a curving, so that the superior end is drawn dorsally before it projects ventrally in the pontine enlargement. The mesial margin of this part
is irregularly curved toward the mid-line (figure 1); the lateral margin shows
a marked mesial notch, superior to which it i)rojects irregularly laterally to
fuse with the pontine nuclei. The nuclear material in the middle of this part
is split into two masses which soon unite (figure 1). Cephalic to the union
of these two masses, the ventral surface is smooth and widens gradually;
about its middle is a gradual ventral ridge shown in figures 1, 2, and 4.
At the level of the caudal end of the separation of this left arcuate
nucleus into two columns, there occur cell-masses belonging to the arcuate
system, dorsal to the ventral mass, lying deeply along the side of the anterior
longitudinal fissure as it deepens into the foramen caecum. A small irregular
cuboid mass and a more ventral elongated mass appear in figure 4 at this
level, t^'omewhat superior to this, the lateral surface of the longitudinal
fissure is lined bj' a cell-column which joins the ventral arcuate mass in a
gentle curve (figure 4). This dorsally projecting cell-column is thickened
at its ventral origin, but soon becomes a slender spur. Cephalic to this,
the whole arcuate plate curves around to the mesial surface. This is continued into two marked dorsal spurs before it merges with the pontine nuclei
which surround the pyramids. The middle of these dorsal spurs is projected
toward the mid-line in a ridge-like (>minence. The whole arcuate complex,
curving around the pyramids and exhibiting the characteristics mentioned,
is shown in figure 4. The fusion of this convex plate with the ventral pontine
nuclei is well shown. The inner surface (lateral and dorsal) of this curved
comjilex is grooved ])y cephalo-caudal fissures and marketl by a single ridge
which lies in the same plane as the cuboid mass and runs in the same cephalocaudal direction.
The right nucleus arciformis is considerably different from the left, which
has just been described. In general, it consists, like the left, of a slender
caudal mass of cells which widens laterally and curves about the mesial
side of the pyramids cejjhalad to fuse with the pons. The most caudal
68 A Reconstruction of the Nuclear Masses in
cell-mass of this right arcuate nucleus begins slightly caudally to the left
as a rather broad and thin column of cells which decreases in transverse
diameter very cjuickly (figiu'es 1 and 10). Reaching a fairly constant transverse diameter, the cell-column extends cephalad (figures 11 and 12), with
a very marked lateral convexity. It terminates abruptly cephalad on a
level below the superior ending of the first portion of the left arcuate. Its
superior pole terminates much farther laterally' than on the left. This allows
it to approximate the olive more closely as the pyramids decrease laterally
in their dorso-ventral diameter. The middle of this first portion of the
right arcuate is marked by a deep lateral notch on its mesial surface.
Cejihalic to this first portion, the curve of the right arcuate nucleus
is further continued medially by a small isolated mass of arcuate material,
irregularly shaped (figure 1). Superior to this irregular mass, on a level
with the division of the left arcuate in two columns, lies the caudal end of
the cephalic portion of the right nucleus arciformis. This shows on ventral
view (figure 1) as two caudally projecting columns, the mesial being more
caudal. This mesial spur is really the ventral border of a mesial plate,
similar to that on the other side, which extends from this point to the pontine
nuclei. It is quite a thick plate, bordering the deepened anterior longitudinal fissure and placed mesially to the pyramid. It shows a number of
short dorsal spurs, more numerous and less extensive than those on the left.
This mesial plate curves around the pyramids into the ventral plate, at the
caudal lateral corner of which is the lateral of the s])urs. Above this spur
is a fairly deep, well-differentiated furrow, with a cephalo-caudal direction.
The middle of this jjortion shows the same gentle ventral ridge as exhiliited
on the opposite side. The lateral margin of this portion of the nucleus is
irregular and shows but little lateral deflection until it suddenly widens into
the ventral portion of the nuclei pontis. The ventral and mesial jjlates fuse
without irregularity into the caudal portion of the j^ontine nuclei. The inner
surface (lateral and dorsal) of this curved plate of cells is marked by longitudinal fissures and furrows, similar, in all main characters, to those which
occur on the left. These ridges are continued upward to mark the course
of the pyramids through the nuclcM ]iontis (figure 13).
The two arcuate nuclei fuse in the mid-line, the connection taking place
just dorsal to the anterior longitudinal fissure (figure 1). Both mesial plates
send out a rather heavy nuclear column and these merge in the mid-line.
The connection, however, ceases before the pons is reached. In the pons,
of course, the mid-line connection of the two nuclei can be assumed.
CORPUS PONTO-BULBARE.
This bod}'- which Mssick {loc. cit.) .showed to extend from the emergent
fifth nerve caudally between the seventh and eighth nerves and to terminate
in the lateral wall of the fouiih Ncntricle just caudal to the dorsal nucleus
of the cochlear nerve has been modeled in this reconstruction. Only those
The Lower Portion of the Human Brain-Stem. 69
parts, however, which contained sufficient nuclear material to justify modeling have been includetl. As one passes from the spinal cord cephalad in
series, the corpus is first met in the lateral wall of the ventricle just dorsal
to the caudal half of the medial vestibular nucleus. This most caudal
portion of the corpus is shown in the I'econstruction as an oval of nuclear
tissue on the dorsal surface of the middle of the caudal half of the medial
vestibular nucleus (figures 2 and 3). Traced from this i)oint cephalad, the
corpus for a short distance loses most of its nerve-cells. As the amount of
nuclear material is not sufficient to justify modeling, no connection is shown
in the model between this most caudal oval and the more cephalic portions.
The tract next becomes sufficiently endowed with nuclear material in the
region just caudal to the most inferior portion of the dorsal cochlear nucleus.
Here it is represented (figures 1, 2, and 3) by a thin sheet of cells, lying caudal
and mesial to the dorsal cochlear nucleus. It is curved by the corpus
restiforme upon which it lies. Its cephalic border is prolonged ventrall}^,
mesially to the dorsal cochlear nucleus. An abrupt termination has been
given to the cori)us at this point by the ending of the sections in the block
of tissue used as a unit for embedding. It is met, however, as soon as the
correction for loss in the blocks is made, lying mesial to the caudal extremity
of the ventral coclilear nucleus in the same dorso-\entral plate. This is
shown in figure 3. From this point, the corpus ponto-l)ulbare is represented
by a continuous cell-mass stretching to the nuclei pontis. Beginning here,
mesial to the caudal limit of the ventral cochlear nucleus, the corpus forms
at first a widening mass of cells with the long axis transverse (figures 1, 3,
12, and 13). Shortly after its origin, it spreads transversely toward the
mid-line in an irregular arm of nuclear tissue which stretches mesially anil
somewhat dorsally toward the substantia gelatinosa and the nucleus of the
seventh nerve. Two small cell-masses occur ventral to this arm (figur(> 1).
The main cell-column of the corpus passes cephalad, \entrally, and slightly
laterally, following the line of the ventral cochlear nucleus. It broadens
somewhat at the cephalic limit of this nucleus and gives origin to two mesially
and dorsally projecting arms, one of which fuses with the cell-column from
the s])inal nucleus of the vestibular nerve and the other with the colunm
from the superior nucleus, as these two columns meet the entering vestibular
nerve. These two projecting arms from the corpus ponto-bulbare are
marked by great irregularities by spurs projecting in every direction, by
sudden increases and decreases in diameters, and by small isolated cellmasses occurring along the course of the nerves. The cephalic end of the
mesial of these two arms comes into contact with tlie substantia gelatinosa.
The main cell-mass of the corpus, decreased in size after the projection of
these two arms, continues cei)halad beyond the cephalic pole of the ventral
cochlear nucleus. This is shown in figures 1, 2, and 3. A thinner mesial
column of cells accompanies the main mass (figure 1, csjiecially). The main
mass and the smaller mesial colunm extend cephalad witli a slight \-entral
70 A Reconstruction of the Nuclear Masses in
deflection (figure 2), and at the caudal end of the nuclei pontis the main cellmass is deflected mesiallj^, still maintaining its ventral deviation. The mesial
column of cells joins very quickly the main cell-column as it is deflected
mesially and the two combine into an irregularly shaj^ed cell-mass which
soon fuses with the pontine nuclei (figures 1 and 3). This mesially inclined
portion of the corpus is split into two masses in part of its course; it possesses
numerous spurs and other irregularities throughout its course.
Not directly connected with the main cell-mass, but separated by a
small distance at the point where the main cell-mass of the corj^us pontobulbare deflects mesially, is a long, heavy cell-column which stretches from
this point to the superior termination of the model. This irregular cellcolumn, placed in the midst of the brachium pontis, extends ventrally and
cephalad in a fairly straight course (figures 1, 2, and 3). It ]3ossesses at
its caudal end a considerable knob-like dilatation, but as it passes cephalad
it becomes flattened transversely. Just cephalic to the caudal end the cellcolumn divides into a smaller mesial portion, which slowh' approaches the
nuclei pontis, and the main lateral column which continues the straight
cephalo-ventral course. Between these two cell-columns and the main mass
of the pontine nuclei are many bizarre nuclear masses. Some make direct
connection between the two masses of nuclear material; others are merely
isolated cell-clusters; others are short columns. All combined render the
jiicture one of great complexity, as shown in figure 1 especially and in figure 3
to a lesser extent.
On the right side of the model, the corpus ponto-bulbare has been modeled from the mesial side of the ventral cochlear nucleus to the pons. It shows
the same general characteristics as are shown in the left side of the model.
The significance of all these irregular collections of cells occurring in
the brachium {)ontis is probably the same as that of the cor})iis ponto-bull)are,
of which they should be considered a part. The corpus probably joins with
the nuclei pontis in many different ways in the different adult brain-stems,
but in general this comjjlicated and bizarre plan of the numerous cell-masses
in the brachium pontis must be granted. This is surely substantiated bj'
the consideration of the conception that the corpus ponto-bulbare is the
pathwa}^ along which migrate the nerve-cells which are to form the nuclei
l^ontis; and in such a nngration, the possibility of the existence of scattered
cell-masses in the brachium ])ontis of the adult is very great.
NUCLEI PONTIS.
The pontine nuclei, in this reconstruction, have been modeled in their
caudal portion, extending cephalad to the limit of the model. For the most
part, no account has been taken of the transversely coursing fiber-bundles
because of the fact that these bundles are discrete and usually extend only
through three or four sections of 40 micra each. This renders reconstruction
of the individual nuclear masses in the nuclei pontis practically impossible,
The Loiver Portion of the Human Brain-Stem. 71
and worthless from a inoriihologieal standpoint. However, on the lateral
surfaces of the pons the {iber-l)undles do make fairly definite pathways in
the gray matter, permitting these to be modeled with some benefit. The
gray matter surrounding the longitudinal fibers of the pyramids has been
modeled, and all of the longitudinal fibers in the neighborhood of the main
mass of jjyramidal filK>rs have been cut away. This gives rise to the resulting
nuclear shell about the pyramids, not shown in any of the drawings of the
model, but seen in figure 14 on cross-section.
The nuclei pontis in the caudal part may be considered as a huge mass
of cells surrounding the pyramids. The portion dorsal to the pyramids
takes its caudal origin just inferior to the superior pole of the nucleus olivaris
inferior (figure 2), while the ventral portion is extended caudall}- into the
nuclei arciformes (figure 1). The lateral portion is continuous caudall}^ with
the corpus ponto-bulbare (figure 1). The pyramids take a fairly direct
cephalo-caudal direction through the portion of the pontine nuclei modeled,
although at the superior end of the model they are divided into many separate
bundles by invading spurs of nuclear material (figure 14). With the dorsal
portion, arising caudally near the superior pole of the oliva, its cell-mass
quickly enlarges in all directions and joins with the ventral portion, at the
cephalic end of the arcuate nuclei, to surround the pyramids. This is shown
in figure 2, the pyramids of course not appearing in the drawing. As soon
as the pyramids are completely surrounded by gray matter, the pontine
nuclei enlarge cephalad in all directions (figures 1, 2, and 4). The dorsal
portion extends dorsally as one goes cephalad; the lateral i)ortion extends
laterally; and the ventral extends ventrally. Such, then, is the general
ground plan of the pontine nulcei in the caudal portion modeled.
When viewed laterally (figure 2) the relations of the corpus pontobulbare and the arcuate nuclei to the pontine nuclei are evident. The caudal
margin of the pontine nuclei extends in a dorso-ventral direction from the
mesial and ventral i)lates of the arcuate nuclei, surrounding the pyramids
and fusing with the small dorsal part of the pontine mass. From this point
of fusion the lateral border, caudally, takes a cephalic deflection and a general
dorsal course, so that it comes into relation with the nucleus nervi trigemini
and its sul:)stantia gclatinosa (figures 2 and 14). This lateral wall is, in its
caudal part, merely a thin sheet of cells projecting dorsally far beyond the
limits of the main nuclear mass. From lateral view, the ventral margin
shows the continuation of the ventral curve exhibited by the most cej^halic
lX)rtion of the arcuate nuclei. This convexity continues upward for some
distance with the assumption of almost an exact cephalo-caudal direction;
it is ended in an angle to be succeeded by a second ventral convexity. This
change in direction probably corresponds to the irregular surface-markings
of the ventral bulging of the pons. The whole lateral surface shows a
cephalo-lateral deviation from the longitudinal plane and also a gradual
convexity from its dorsal border around the pyramids to the mid-line. This
72 A Reconstruction of the Niiclear Masses in
surface is marked by excessive irregularities, as shown in figures 2 and 14.
The strilving features of these irregularities lie in the direction of the spurs
and in the nuclear connections between the corpus ponto-bulbare and the
pontine nuclei, which have already been described. The surface is studded
by the spaces filled by the ponto-cerebellar fibers as they leave the pons to
course through the brachium pontis to the cerebellum. Between these fiberbundles numerous nuclear spurs project in a dorso-lateral direction. The
character and abundance of these spurs is shown in figure 2; they are most
numerous and tyjjical in the middle of the lateral surface, where they are
extensive, large, and separated by deep fiber fenestrations.
As one moves from the lateral to the ventral surface, the surface irregularities are seen to change gradually until they assume a fairly typical form
on the ventral surface. Here the surface (figure 1) shows short and shallow
furrows, deeper sulci, and many ridges more or less extensive. These run
in all directions in the upper part, although in the most caudal portion their
long axes are in the main transverse. The ventral surface exhibits the ventrocephalic deflection a))ove noted and two convexities merging in the mid-line
in an irregularly delimitetl furrow. The lateral walls of this mid-line depression, as shown in figures 1 and 4, are marked In' bizarre sjuirs and notches.
The base of the furrow is marked by irregular corrugations and is wider than
its ventral opening. It is filled with transversely coursing fiber-bundles
which give rise to marked i)erforations of the lateral nuclear walls.
On mesial view (figure 4) the mass of nuclei pontis is shown cut along
the mid-line. The more cephalic origin of the caudal part of the pontine
nuclei, in the mid-line, is well shown. The mesial plate of the arcuate
nucleus has become fused with the ventral j^ortion of the ]iontine nuclei,
some distance caudal to the point where the pontine nuclei cross the nudline. The dorso-cei)halic slope of the main dorsal pontine cell-mass is shown
extending from the dorsal margin of the mesial plate of the arcuate nucleus.
This surface is met, in the middle of its course in the model, liy the dorsal
margin of the nuclear material which crosses the mid-line. This dorsal
margin of the mid-line gi'ay matter is shown in figure 4, as an irregularly
notched and fissured border, witli three chief notches and two caudal projections marring its outline.
The dorsal surface of the nuclei pontis is not shown in any of the drawings, but its outline ai)pears in figure 4. Beginning caudally at a ratiier
sharp pole just caudal to the superior termination of the oliva, this dorsal
surface, as one progresses cej^halad, widens out dorsally and laterally. It
(juickly joins with the mesial and ventral jilates of the arcuate nucleus to
siwround the i)yramids. When viewed from the dorsal side, this surface
shows two ventral concavities which end in inesial and lateral dorsal i)rojections. Tlic hiteral projection forms tlic miclear i)latc of the lateral pontine
wall, while the mesial dorsal projection runs along the mid-line to expand
info the nucleus I'cticularis tegmenti ])ontis (figures I and It). Between the
The Lower Portion of the Human Brain-Stem. 73
two dorsal projections is the main concavity of the surface of each side.
This becomes less marlced as one goes cephalad. The surface is irregular!}^
fissured and furrowed, showing between these groovings many small dorsal
projections.
The relations of the dorsal end of the lateral plate of the pontine complex with the nucleus of the nervus trigeminus are worthy of comment. On
a level with the superior pole of the nucleus nervi facialis the lateral plate
of the pons projects dorsally and meets the substantia gelatinosa just as that
merges into the sensory enlargement (figure 4). This projection of tissue
from the nuclei pontis lies mesial to the lateral wall of the complex and the
lateral cell-mass overhangs it. The separation of the nuclear material from
the pontine nuclei and that composing the trigeminal complex is very difficult. Traced cephalad from the caudal point of union of the trigeminal
luicleus and the pontine nuclear material, the connection between the dorsal
l)ontine mass lying mesial and ventral to the trigeminal nucleus is broken
for a considerable extent. This is shown in figure 2. The dorsal mass of
pontine cells projects in a laterally directed ridge and then suddenly recedes
as the connection is again made at the upper extremity of the model. Here
the connection between the dorsal pontine mass and the lateral wall of the
nuclei pons is tjuite massive. On mesial view the dorsal pontine mass is
seen to extend quite a distance dorsally toward the mesial eminence on the
surface of the fifth nucleus.
The nucleus reticularis tcgmcnti pontis (Flcchsig) is the dorsal projection
of the mesial portion of the dorsal surface of the nuclei pontis. It really
represents a portion of the nuclei pontis lying along the mid-line of the
tegmentum and projecting dorsally almost beneath the floor of the fourth
ventricle (figure 14). Its mesial outline is shown in the transparenc.y of figure
4 as the irregular continuation of the dorsal surface outline of the pontine
nuclei. As modeled, the nucleus shows two distinct portions, a marked
laterally projecting mass, irregular in extent and marked by a bizarre surface,
situated midway between the dorsal surface of the nuclei i)ontis and the
floor of the fourth ventricle, and a second dorso-lateral projection beneath
the nucleus incertus in the floor of the ventricle. These two masses are
connected by a broad irregular bridge of nuclear material. The more ventral
of these two masses shows a gradual increase in extent as it proceeds cephalad ;
at its caudal portion it is marked by a deep cei)halo-caudal furrow. It
continues beyond the cephalic limit of this model. Its surface is marked
by many irregularities, especially by deep fissures. The dorsal of th(> two
masses projects dorso-laterally as a bizarre and heavy cell-column, which
shows a peculiarly shaped triangular caudal projection (figure 4) . The dorsal
surface curves laterally and dorsally beneath the nucleus incertus. This
spur recedes as it goes cephalad and, after a marked notch, a second dorsolateral spur takes its place beneath the nucleus incertus. This terminates
as the superior margin of the model is reached (figure 4).
74 A Reconstruction of the Nuclear Masses in
The course of the pyramids through the portion of the nuclei pontis
included in this model is almost a direct longitudinal one. At the caudal
end of the pontine nuclei, the pyramids form a solid column of fibers surrounded by the cell-mass of the pons. The cross-section in this area (figure
13) shows them to bo almost round. The investing nuclear wall is smooth,
marked only by the longitudinal ridge mentioned as occurring on the inner
surface of the plates of the arcuate nuclei. As the pyramids are traced
cephalad, small spurs project from the including nuclear tissue separating
the fibers. Cephalic to these small spurs, occur cell-bridges which divide
off a portion of the fibers from the chief bundle of the pyramids. These
cell-bridges increase in number and extent, breaking the pyramids up into
smaller collections of fibers. Such, then, is the course of the pyramids
through the pons, as shown in this reconstruction. This is not given in
any of the drawings of the model, but the breaking up of the main Inuulle
of the pyramids appears in the cross-section (figure 14).
NUCLEUS OLIVARIS SUPERIOR.
The nucleus olivaris superior begins just caudally to the middle of the
nucleus nervi facialis and, sloj^ing dorsally and slightly laterally, terminates
ce{)halad in the region of the sensory enlargement of the nervus trigeminus
(figure 4). It measures in its longest diameter 9.0 millimeters. It lies along
the ventro-mesial surface of the nucleus of the seventh nerve in its extent
and then gradually ai)i)roaches the ventral i:>ortion of the mesial surface of
the nucleus nervi trigemini. It is mesial to the lateral wall of the pontine
nuclei. On its mesial side and ventral side lies the formatio reticularis, in
which it occurs; superior to the nucleus of the seventh nerve, it has formatio
reticularis also on its dorsal and mesial asj^ects (figure 13).
The caudal termination of this nucleus olivaris superior is a pointed
pole lying in close ai)i)roximation with the ventro-mesial surface of the
nucleus of the seventh nerve. It is shown in figure 4, the mesial view of the
model. This inferior portion of the nucleus is poorly defined and is separated with difficulty from the nucleus of the seventh nerve, even though
the latter possesses a characteristic histology. The nucleus enlarges into
a triangular nuclear mass, out of which three dorso-ventral cell-columns
appear clearly defined. These are luiited at their ventral aspect and they
spread out from this ventral point as spokes from a hub. Dorsally the ends
of these ridges are joined together at a level slightly su])erior to the point of
ventral radiation. The two cell-columns which form the nucleus arise from
the ventral and dorsal points of union, respectively, and run cephalad,
dorsally, and somewhat laterally (figure 13).
The mesial column arises from the ventral ]ioint of radiation in the
caudal cell-collection, as a small continuous ccll-ma-ss. This ((uickly and
abrui)tly enlarges into a thin sheet of cells which run cephalad in the characteristic direction. This .sheet of cells lies in the general dorso-ventral plane,
The Lower Portion of the Huvmn Brain-Stem. 76
but its ventral border is placed more laterally from the mid-line than its
dorsal margin. The mesial surface is smooth and slightly curved, with a
mesial convexity extending cephalad for half of the extent of the nucleus,
where it forms a marked notch. The surface then extends mesially in a
small shoulder. Just posterior to this notch is a deep caudal incision, dorsal
to which appears a similar, somewhat thicker sheet of cells (figure 4), which
merges with the mesial cell-cohmm, the two ascending as a widened, thickened
cell-sheet in the characteristic direction of the columns in the nucleus. Just
caudal to the cephalic termination, the ventral border turns abruptly dorsally
and then cephalad, decreasing the width of the cell-sheet by almost one-half.
This is quickh' followed by the abrupt cephalic ending of the nucleus, the
cell-sheet disappearing very quickly. The ventral border of this mesial
cell-column shows a slight ventral projection somewhat cephalad to its
caudal origin. Slightly above this, the dorsal border exhibits a dorsal projection (figure 4). The mesial surface is smooth, but in the caudal half is
marked by a slight eminence and in the ventral portion of the cephalic half
a similar eminence occurs. Cephalic to this superior elevation, the mesial
surface shows a slight concavity. The lateral surface of the mesial cellcolumn is quite irregular and rough. At a point corresjionding to the notch
in the mesial surface, a marked irregular lateral projection occurs on this
surface. At the superior pole there is considerable thickening of the nucleus
in the transverse diameter.
The lateral of the two cell-columns is really double throughout the middle
portion of its extent, although it arises singly from the mesial surface of the
dorsal union of the three primary radiate columns. Arising from this union,
the column extends as a triangular cell-column, placed dorsally and somewhat mesially to the dorsal border of the mesial column. It approximates
in part the ventro-mesial border of the nucleus nervi facialis (figure 4). It
continues cephalad somewhat irregularly, in the characteristic dorsal deflection, with slight lateral deviation. At the level of the superior pole of the
seventh nucleus a marked and smooth dorso-mesial spur is given off. At
this point the cell-column bends laterally and dorsally across the superior
pole of the olive and then pursues a cephalo-lateral course to fuse quickly
with its second portion. This second portion of the lateral column arises
just caudally to the superior pole of the seventh nucleus as an elongated oval,
with the long axis in the dorso-ventral plane. It ascends cephalad and fuses
with the lateral cell-mass after its abrupt lateral deflection. Here the combined cell-column, oval in shape, lies lateral to the mesial collection. It
passes cephalad in the characteristic direction of these cell-columns, flattening out as a dorso-ventral sheet of cells. As such, it abruptly terminates
just caudal to the lateral jirojection on the lateral surface of the mesial cellcolumn. Hence the lateral column possesses only half the longitudinal extent
of the mesial cell-mass.
76 A Reconstruction of the Nuclear Masses.
ACKNOWLEDGMENTS.
I take pleasure in acknowledging my thanks to Dr. F. P. Mall, to Dr.
Florence R. Sabin, and especially to Dr. C. R. Essick for their encouragement and practical assistance throughout this work, and to Mr. Max Brodel
for his drawings of the reconstruction.
The work was done at the Anatomical Laboratory of the Johns Hoi)kins
University between 1909 and 1913, and has received substantial aid from
the Foundation "Art in Medicine," Johns Hopkins Medical School, and
from the Carnegie Institution of Washington.
BIBLIOGRAPHY.
1881. C. F. VV. Roller, Arch, f. Mik. Anat., vol. xix, p. 383.
1891. Ij. Blumen.\u, Neurologische.s CVntralblatt, vol. x, p. 220.
1897. F. R. S.\Bi>i, Bull. Johns Hopkiii-s Hospital, vol. viii, p. 2.53.
1901. F. R. S.\BIN, Atlas of JMiMlulla aiul Mid-hraiii, Baltimore, and Johns Hojjkins Hospital Reports, vol. ix.
1902. G. L. Streeter, Ainer. Journ. Anat., vol. ii, p. 299.
1903. E. L. Mkllus, Amer. Journ. Anat., vol. ii, p. 361.
1906. A. Van Gehuchten, Anatomie du Systeme Nerveux de L'hommo, Loiivain.
1907. C. R. Essick, Amer. Journ. Anat., vol. vii, p. 119.
1909. L. Jacobsohn, Kerne des menschlichen Hirnstamms, .Vhhandl. d. Konigl. Preuss. .^kad.
1912. C. R. Essick, .\mer. Journ. Anat., vol. xiii, p. 2.").
EXPLANATION OF PLATES.
KEY TO LECiEXDS IN FIGURES.
ah, Undest'ribcd nucleus (I'f. text, p. 27) (orange).
ac, Nucleus alsc cinereir (purple).
am, Nucleus ambiguus (uncnlored).
ar, Nucleus arciformis (yellow).
eg, Substantia grisea centralis (uncolorcd).
CO, Nucleus nervi cochlea! (purple).
cii, Nucleus fasciculi cuneati (red).
fr, Formalio reticularis (luicolored).
ft, Nucleus funiculi teretis (green).
gr. Nucleus fasciculi gracilis (yellow).
in, Nucleus intercalatus (blue).
ic, Nucleus incertus (purple).
la. Nucleus lateralis (green).
tnc, Anterior motor column (red).
oil. Nucleus olivaris accessorius dorsalis (orange).
ol, Nucleus olivaris inferior (uncolored).
oin. Nucleus olivaris accessorius medialis (orange).
OS, Nucleus olivaris superior (violet).
pb. Corpus ponto-bulbare (yellow).
po, Nuclei pontis (yellow).
TO, Nucleus of Roller (green).
Is, Nucleus tractus .solitarii (uncolorcd).
vc, Nucleus nervi vestibuli (green).
vm, Nucleus motorius nervi trigemini (uncolorcd).
vs. Nucleus sensorius nervi trigemini (blue).
vi, Nucleus nervi abducentis (red).
vii, Nucleus nervi facialis (uncolored).
xii, Nucleus nervi hypoglossi (red).
Fig. 1. Drawing of the ventral aspect of the whole model (X 7.5). The heavy pontine mass is prolonged
caudally in the form of intcrrujited arcuate nuclei. The latter bow away from the mid-line on both
sides and lie in front of the two oliva". At their termination the anterior columns of the spinal cord
extend to the base of the model. The outlines mark the configuration of the brain-stem and end
cephalad to the lateral recess, .\long the margins are given the levels of the sections, represented
in figures 8 to 14.
Fig. 2. Drawing of the left lateral aspect of the model (X 7. .5). The prominent pontine nuclei overhang
the olive and an arrow passes through the roughened tunnel in the graj- material formed by the
pyramidal tract in its crossing. The ventral limit of the brain-stem is outlined in its entire extent.
Dorsally the margin is discontinued at the dorsal (Cochlear nucleus, where it runs toward the cerebellum as the anterior wall of the lateral recess.
Fig. 3. Drawing of the dor.sal aspect of the model (X 7.5). To the right of the mid-line, the nuclei of the
upper cervical cord are rc[)resented, but where the central canal expands into the fourth ventricle
the smooth surface of the floor has been retained. On the left side, all the nuclear masses have been
modeled separately. The ink line marks out the configuration of the brain-stem as far as the outline
is not a knife cut made in preparing the specimen.
Fig. 4. Drawing of the mesial aspect of the left half of the model (X 7.5). The pontine mass, the nucleus
reticularis tegmenti pontis, and the caudally projecting arcuate nuclei are represented as transparent. The central canal of the spinal cord is shown in dotted lines which are continued into the
fourth ventricle as far as the nucleus intercalatus. The surface form is represented in outline on
the ventral side, while dorsally this line is continued in the region of the anterior wall of the lateral
recess, as in figure 2.
Figs. 5, 6, 7. Drawings of the ventral, mesial, and dorsal aspects, respectively, of the nucleus olivaris
inferior (X 7.5). The first, second, and third primary fissures arc designated in these figures by
the constant initials of a, b, and c, on the ventral and dorsal surfaces. The form and jjosition of
the nucleus olivaris accessorius dorsalis is portrayed by a simple outline.
Figs. 8, 9, 10, 11, 12, i:i, 14. Drawings of cross-section (X 2.4) representing respectively sections 5, 2()(),
400, 500, ()()0, 700, and 900, which have been selected from the series used in this reconstruction.
The accom[)anying outline drawings show the limits of the nuclear masses, with the same color
representations as in the other figures. The iiosition of these sections in the model is given by
the various section-levels in the first four figures.
78
PLATE I
Fig. 2
Fig. 3
PLATE IV
fig. 4
PLAte V
Figr. 5
Fig. 6
Fig. 7
Fig. 8
Fig, 10
Fig. 9
Fig. 11
Plate vi
Fig. 12
Fig. 13

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