Te Deuioi if i Ims Test; sc i 
Dm In 
BY 
DR- H- D- Schmidt, 
Member of the American Neurological Assoc.ation. 
{Reprinted from the Journal of Nervous and Mental Disease, July, 1877.) 
CHICAGO: 
A. S. Kissell & Co., Printers. 
1877. TffiMel. 
Drawn from nature hy the author, 
Henry Lithographer. N O. TfflMd? III. 
I)ra\\n frun nature by the author, 
Henry Klun$. Lithographs. .VO Tv. bl pill. 
Drawn from nature bv the author, 
Henry Kiting Lithographer. NO. THIS 
JOURNAL 
OF 
Nervous and Mental Disease 
Vol. IV. JULY, 1877. No 3. 
j\rficlcs, ami translations. 
Art. I.—THE DEVELOPMENT OF THE NERVOUS 
TISSUES OF THE HUMAN EMBRYO. 
By Dr. II. I). Schmidt, of New Orleans. 
Member of the American Neurological Association. 
THE following pages embody the results of a series of re- 
searches into the development of the nervous tissues of 
the human embryo, which were commenced several years ago. 
More than four years, indeed, have elapsed, since they were 
finished, but not until now have circumstances allowed me to 
present them to the medical public in proper form, and illus- 
trated with appropriate drawings. It is true, that some refer- 
ence was made to these investigations in my article on “The 
Structure of the Nervous Tissues” etc., published in the Tran- 
sactions of the y earl 8 7 5, of the American Neurological Asso- 
ciation ; but oidy such a brief sketch was given, as the ar- 
rangement then in hand required. 
I was fortunately able in these researches to command an 
abundant supply of good material. The greater portion of 
embryos employed—about eighteen in number—belonged 
chiefly to periods of pregnancy, anterior to the fifth month. 
In all, they ranged from one exceedingly small specimen, only 422 
Schmidt—Development of the Nervous Tissues. 
(>. mm. in length, through all the intervening stages of foetal 
evolutions, up to the mature foetus horn at full term. 
The examinations were made, as circumstances required, 
both from fresh specimens and from others preserved and pre- 
pared in a weak solution of chromic acid. 
Inasmuch as the nervous tissues are not developed from 
organic cells, in any true sense of the word, as has been so 
generally supposed, I have deemed it expedient to introduce 
the subject with some prefatory remarks in explanation of 
some terms, which 1 have employed. 
Ever since the discovery of the organic cell in animal tissues, 
it has been a favored theory, among histologists, that the pri- 
mary form of all tissues was that of a cell. This theory still 
almost universally prevails, although in one instance, at least, 
in the so called “white fibrous” or connective tissue, it has 
been sufficiently shown, that it does not originate in a cellular 
form. But neither the striated muscular, nor the nervous tis- 
sues originate from cells, unless we look upon the nuclei, con- 
cerned in their origin and development as such. The idea, of 
what constitutes an organic cell itself, has of late years under- 
gone considerable modification, since it was discovered, that 
the only essential part of this body, was the protoplasm, and 
that in many cases the whole cell consisted only of a minute 
portion of this substance. Thus, the wall and the nucleus are 
now considered to be non-essential parts of a cell, both being 
products of the protoplasm. The wall, when present, must 
manifest itself by a double contour; a cell, presenting only a 
single contour, is said to possess no wall. And yet, it seems 
to me, that even in this instance, the density of the proto- 
plasm must be greater at its surface, than in the interior of the 
mass; for, if there were no limiting elements, the protoplasm 
of contiguous cells would be liable to become fused. Such a 
layer may differ so slightly from the whole mass of protoplasm, 
of which it forms a part, and may be so extremely thin, as 
to manifest itself only by a delicate single contour, and never- 
theless, its density may be sufficient, to prevent its fusion with 
a neighboring cell. 
The nucleus, which, according to the older cell theory, was 
pre-existent to protoplasm, as well as to the wall, is now known Schmidt—Development of the Nervous Tissues. 
423 
to originate from and within the protoplasm. There are, how- 
ever, some exceptions to this rule. 
According to what has been said above, a nucleus, sur- 
rounded by a portion of protoplasm, however minute or of 
whatever form, constitutes a perfect cell. But, now I may 
ask, whether the term “cell” may equally be applied to a body 
•consisting of a more or less oblong nucleus with a minute por- 
tion of protoplasm, in the form of granular filaments or ap- 
pendages, adhering to its opposite poles? Such bodies are met 
with in the developments of the striated muscular fibres 
(Fig. 4), and in that of the smaller blood vessels in the human 
embryo. To extend to these bodies, the term “cell” appears 
to me to overstretch the true meaning of the word. It was 
for this reason, that sometime ago, in connection with my re- 
searches of the development of the smaller blood vessels in 
the human embryo, I preferred to call these elements “spindle- 
shaped bodies,” and I shall make use of this term in the fol- 
lowing pages. It is true that in the development of the 
striated muscular fibres the nuclei of these elements become 
eventually entirely surrounded by the granular fibrillae (F 'ig- 
and the whole body might then be compared to an organic 
cell. But, as these bodies soon fuse with each other, in order 
to form another distinct tissue, and thus never perform the 
functions of a true organic cell, I shall still prefer to apply the 
above mentioned term to them, especially, as their fibrillae 
may be easily separated after the fusion has taken place (Fig. 5). 
In the development of the nerve fibres, no such spindle- 
shaped bodies occur, for the nuclei are lying at first free be- 
tween the granular fibrillae, only later, when the axis cylin- 
ders begin to be formed, they become fused with fibrillae. 
The nervous tissues, during the earlier stages of develop- 
ment, are exceedingly delicate, of a jelly-like consistency, and 
to a certain degree transparent. It is this delicacy of struc- 
ture which renders their histological investigation so difficult, 
as it frequently interferes with their successful removal from 
the body of the embryo. In very small embryos, therefore, 
it becomes often necessary to immerse them for a short time 
in a weak solution of chromic acid, in order to render them 
sufficiently consistent for dissection. If the solution is not 424 
Schmidt—Development of the Nervous Tissues. 
strong, and the material is only exposed a short time to its 
action, the changes taking place in the tissues by its action 
will be so slight, as not to interfere with the investigation. 
Nevertheless, in order to come to correct conclusions, the ex- 
aminations made of specimens treated with a solution of 
chromic acid, should always be compared with such as are 
made from fresh unaltered material. 
Another difficult point in the investigation of embryonic 
tissues, is to determine the* exact age of a human embryo, 
especially when we obtain our material from unknown sources. 
To estimate the age of an embryo bjT its size is inadmissible, 
as embryos of the same age and stage of development may 
differ in size as well as adults do. To avoid errors, I shall 
therefore state in the following pages simply the length of 
embryos under discussion, measured from the top of the 
head to the point of the big toe, and allude to their ages only 
approximately. 
The smallest embryo, which I ever had occasion to examine, 
measured f> mm. in length, (Fig. 1.) The brain here, con- 
sisted only as far as 1 could ascertain, of the same embryonic 
elements as the dermal surface and other tissues; viz., of 
small embryonic nuclei, embedded in a soft, somewhat trans- 
parent material, the protoplasm. A differentiation of the 
nervous tissues, and those surrounding them, had as yet, not 
begun. 
In examining the nervous matter of the brain of embryos 
of about 9 mm. in length (Fig. 2), we find it to consist of an 
amorphous matter of a gelatinous consistency, holding, besides 
innumerable minute granules, a very considerable number of 
nuclei (Fig. 7, a). The greater portion of these nuclei present 
an oval form, some of them are round, while others have 
assumed more or less the form of a spindle. They all present 
a distinct double contour, and contain a number of granules, 
frequently unequal in size.- On some of the nuclei, small ap- 
pendages in the form of granular filaments, were observed to 
adhere to their opposite poles. It is difficult to decide, 
whether these bodies were the primary representations of 
ganglionic bodies, or whether they were destined to take part 
in the formation of blood vessels. Besides these elements,. Schmidt—Development of the Nervous Tissues. 
425 
a small number of certain cells, tilled with small nuclei were 
observed. The latter, measuring from about Jo to mm. 
in diameter, were distinguished by a very dark and heavy 
contour and by a greenish lustre. In most instances, no cell 
membrane could be seen, the whole represented a minute ball 
of nuclei (Fig. 7, b). To these cells we shall refer again here- 
after. Some other elementary forms, observed in the matter 
of the brain at this embryonic period, remain to be men- 
tioned. These were a number of long, spindle-shaped 
opaque bodies, containing one or more rows of granules. 
Some of these bodies already adhered to each other (Fig. 7, 
<?). They undoubtedly represented the first traces of the 
blood vessels, and judging by the resemblance they bore to 
those spindle-shaped nuclei, above mentioned, they were very 
likely identical with them. In my article “On the Develop- 
ment of the Smaller Blood-vessels in the Human Embryo,” 
published in the January number of the Monthly Micro- 
scopical Journal, 1875, I have described one mode of the 
formation of blood vessels, taking place at a later period, by 
the formation of certain spindle-shaped bodies, consisting of 
granular fibrillse; the latter starting to be formed from the 
opposite poles of a pre-existing oval nucleus, by successive ad- 
hesion of granules, and similar to the formation of the 
striated muscular fibre. The observation of these spindle- 
shaped opaque bodies in the matter of the brain above de- 
scribed, however, seems to indicate that at this early period of 
embryonic life, blood vessels may also be developed directly 
from nuclei. 
Although several embryos of this early period, either of the 
same size or slightly larger, fell into my hands, I never suc- 
ceeded in isolating successfully the spinal marrow for the pur- 
pose of an exact examination. The tissues in general at this 
period are very soft, and their differentiations still too slight 
to admit of an easy separation. But judging from the exami- 
nations made of the spinal marrow of somewhat older em- 
bryos, to be described directly, I suppose, that it consists of 
the same elements as the brain. 
In a perfectly fresh and normal embryo, of about 16 mm. in 
length (Fig. 3), I found the brain to consist of the same ele- 426 
Schmidt—Development of the Nervous Tissues. 
meats as above described, which, however, were now farther 
advanced in development (Fig. 8, a). Thus, the minute 
granules were more numerous, so much so, as to form a granu- 
lar mass or substance. A considerable portion of them had 
already been arranged into rows, forming granular tibrilhc. 
The nuclei were also more numerous, they all presented a dis- 
tinct double contour, and contained a number of granules, the 
largest one of them representing the nucleolus. A few 
granular fibrillar were observed to adhere to some of these 
nuclei (Fig. 8, c). Now, whether this adhesion took place 
accidentally, or whether we behold here the first traces of the 
formation of ganglionic bodies, I am not prepared to decide; 
especially as I did not observe the same phenomenon in the 
spinal marrow of this embryo. 
Finally, a considerable number of clear cells, containing 
coarse granular nuclei, were met with in the matter of this 
brain (Fig. 8, b and d). The outlines of these cells represent 
a delicate, double contour, and being very clear,contain nothing 
else besides the nucleus, except in a few instances in which I 
observed a few single granules. The nucleus consists only of 
a collection of coarse and mostly irregular-shaped granules, 
possessing no enveloping layer or wall. In many instances, 
some of these granules were observed to separate from the 
general mass; while in others they were seen to escape through 
the ruptured wall of the cell. The diameter of the clear cells 
is not constant, for it ranges from 4;';() to 4mm., the 
nucleus, however, whether enclosod by a large or small cell, 
varies but little in size, its diameter being about 4;j0 mm. 
The form of the cell also varies, for, while some of them 
appear round or oval, others are irregular in shape (Fig. 8, d). 
These cells are not only found in the nervous tissue, but also 
in all other tissues during the earlier stages of their develop- 
ment. Considering their general occurrence and the separa- 
tion of the granules of their nuclei, it almost appears as if 
they were playing some part in the multiplication of nuclei. 
As regards the spinal marrow of this embryo, I succeeded 
in isolating a portion of it in the fresh condition. With some 
slight exceptions, it consisted of the same elements, as those 
of the brain just described. A portion of it still consisted of Schmidt—Developmerit of the Nervous Tissues. 
427 
free granules, though the arrangement of these minute 
granules into rows or fibrilhe had advanced much further than 
in the brain, the formation of fibrillm was already so decided 
as to allow them to ' be separated into bundles in the white 
substance. Fig. 10 represents a small portion of the spinal 
marrow in the fresh condition, exhibiting the formation of 
fibrillae. The bundle, lying across the general mass, repre- 
sents most likely a spinal nerve. The nuclei were also more 
numerous; they usually contained one or two nucleoli among 
the granules packed in their interior. They were either dis- 
tributed throughout the whole, as in the white substance, and 
unconnected with the fibrillae, or collected into masses as seen 
upon the pia mater in Fig. 9, a. Those clear cells with 
coarse granular nuclei were also met with here in very consid- 
erable numbers (Fig. 9, b). Besides these, however, a number 
of these mother cells, packed with small nuclei of a greenish 
lustre, alluded to before, were observed in their various stages 
of development. As stated before, some of them represented 
only a minute ball of nuclei, while in others a delicate single 
contour was observed; in these instances, the nuclei were quite 
small. But there were still others, further advanced in devel- 
opment (Fig. 9 c), which were distinguished by a double con- 
tour. In some of these, the nuclei had obtained a considerable 
size, and even showed a double contour. The development of 
the nuclei, however, seemed to bear no fixed relation to the size 
of the celi, neither did the contour of the cells. The whole 
character of these elements shows, that they are mother cells, 
engaged in the multiplication of nuclei. Like those clear 
cells, they are also met with in other tissues, at this early 
period, especially in the skin. In the spinal marrow, these 
cells wrere not observed between the fibrillae of the white 
substance, but they were especially observed in the vicinity of 
the pia mater. It was in this locality also, where the nuclei 
were met with, collected in masses, which circumstance induced 
me to think, that the growth of the spinal marrow in thickness 
was most active near this membrane. In examining a small 
piece of pia mater (Fig. 9), it was found to consist of a deli- 
cate amorphous membrane, the inner surface of which was 
dotted with innumerable granules; a number of these were 428 
Schmidt—Development of tlie Nervous Tissues. 
arranged iti the form of rows. Now, whether these rows of 
granules represent the first traces of the formation of the 
fibrillae of the connective tissue of the membrane, such as T 
observed in other places, or whether they were fibrilhv of the 
nervous substance, adhering to the membrane, I must leave 
undecided. 
In reviewing the results obtained from the examination of 
the nervous tissues of this early period of embryonic life, we 
can not fail to recognize the first traces of the future nerve 
fibre in the form of a row of minute granules, which, held to- 
gether by an intermediate substance, are transformed into 
nervous fibrillae, thus representing the fundamental anatomical 
elements of the axis cylinders. The first traces of the forma- 
tion of ganglionic bodies, or so called “nerve cells” are seen 
in those short fibrillae, adhering to some of the nuclei, as- 
before described. 
To satisfactorily demonstrate the development of the per- 
ipheral nerves at this early period, is very difficult, on account 
of the fact that the striated fibres of the muscles, by which 
the nerves are surrounded, still consist of granular fibrillar, 
rendering it impossible to distinguish between the two tissues. 
But in examining the bundle of nervous matter, lying across 
the fragment of spinal marrow (Fig. 10), and which we may 
safely regard as a spinal nerve that during the manipulation 
was accidentally dragged across the preparation, we find the 
development of its composing fibrillae as far advanced, as that 
of the fibrilla* of the white substance of the spinal marrow. 
No traces of the formation of blood vessels were discovered in 
the spinal marrow at this period. 
A spinal ganglion, which I succeeded in separating in the 
embryo under discussion, I found to consist, like the brain and 
spinal marrow, of a great number of nuclei, imbedded in the 
mass of granules, of which a great number were already ar- 
ranged in rows, representing granular fibri 11a?; even some 
small bundles of them were observed. 
Let us now direct our attention to embryos, about nine 
weeks old, measuring from 5 Tfi0 ct.m. to 5 ct.m., from the 
top of the head to the point of the toes, and of which I had 
occasion to examine some fine specimens thoroughly. In com-' Schmidt—Development, of the Nervous Tissues. 
429 
paring the nervous system of this period with that of the 
small embryo last discussed, we find that during the interven- 
ing time, its morphological development has been proportion- 
ately greater than its histological. In embryos of this period 
the head is still large in proportion to the whole body. The 
eyes and nose are formed; the mouth is open, and its cavity 
quite well developed. The extremities are formed, but the fin- 
gers and toes are to a certain degree still connected with each 
other. The lungs, heart and larger blood vessels are distinctly 
formed, also the liver, spleen, intestines, etc. The farthest de- 
veloped of all is the muscular system, for the muscles not only 
possess their individual sheaths, but they are, moreover, al- 
ready provided with blood vessels. From the advanced devel- 
opment of the heart and the blood vessels, as well as from the 
quantity of mature colored blood corpuscles, it may be pre- 
sumed, that the circulation of the blood is carried on pretty 
completely. In opening the cranium and spinal canal, the 
brain and the spinal marrow with their membranes are found 
to be morphologically much farther developed, than in the em- 
bryo last discussed. The membranes, though still passing 
through their phase of histological development, are neverthe- 
less, formed in all their details. Thus, the pia mater, delicate 
and transparent as it still is, not only embraces the whole 
cerebro-spinal axis, as in later periods, but also extends in the 
form of the neurilemma over the peripheral nerves and their 
ramifications; and notwithstanding its delicacy of structure, 
it can now be separated under water from the nervous tissues 
without difficulty, offering the best opportunity for the study 
of the development of its connective tissue and blood vessels. 
The ganglia of the sympathetic nerve are also distinctly 
formed. They are seen extending along each side of the 
spinal column, forming the gangliated cords. Their size, how- 
ever, in comparing it with that of the perfectiy developed gan- 
gliain the adult, seems rather larger in proportion, for which 
reason they also appear to be closer to each other. 
The nervous substance of the brain and spinal marrow of 
this period, presents a white semi-transparent appearance, sim- 
ilar to the “Milk glass” of certain lamp shades. It still consists 
principally of those primary anatomical elements, already de- 430 
Schmidt—Development of the Ntrvous Tissues. 
scribed. The histological development of these elements, has 
however not kept equal pace with the development in volume 
and form of the whole nervous apparatus. Not only has the 
brain and and spinal marrow assumed a more decided form, 
hut the peripheral nerves are also distinctly formed and may 
even he separated. In the spinal marrow, the gray substance 
is softer than the white. The formation of ganglionic bodies 
is still confined to a small number of nuclei, to which a few 
short granular fibrillae are seen to adhere. The rest, being 
quite numerous, are distributed throughout the granular sub- 
stance, the granules of the greater part of which are now 
arranged into regular rows. The first traces of the formation 
of blood vessels are now observed in the form of oval nuclei, 
with small granular appendages, adhering to their opposite 
poles, and giving to the whole body the form of a spindle. 
In the white substance also, the greater portion of the granules 
are found to be arranged into parallel rows, while the rest are 
distributed between these primitive fibrilla*, to furnish, in the 
course of the developement, material for the formation of 
others. Those subdivisions of the white substance, as seen in 
the fully developed spinal marrow, into larger or smaller bun- 
dles, and effected by partition-like processes derived from the 
neuroglia, may be observed to commence in the embryonic 
spinal marrow of this period. 
An interesting fact to be noticed here is, that while in the 
spinal marrow the granules are arranged, as before mentioned, 
into regular rows, which, however, may be easily deranged 
again by manipulation, in the peripheral nerves, as for instance 
in the brachial plexus, they are observed to be already fused 
with each other into perfect fibrillae. This observation, with 
others to be stated hereafter, shows, that the development of 
the nervous tissue is farther advanced at the periphery, than 
in the centre. 
In the brain the histological development has not advanced 
further than in the spinal marrow. On the contrary, the 
granular fibrillae are not even so distinctly formed as in the 
latter. The formation of ganglionic bodies is still limited to 
those few nuclei with granular filaments adhering, as men- 
tioned before. 
The pia mater extends from the brain and spinal marrow, Schmidt—Development of the Nervous Tissues. 
431 
over the peripheral nerves in the form of a single sheath. 
The whole nerve consists, therefore, like the nerve of an in- 
sect, only of a bundle of granular fibril la1,'which in pursuing 
a slightly wave-like course, are placed parallel to each other, 
and surrounded by their sheath, the neurilemma. A number 
of oval nuclei, varying in diameter, are distributed and im- 
bedded between the fibrillae. The blood vessels of the pia 
mater are very numerous and much further advanced in de- 
velopment than those of the nervous substance. When the 
pia mater is illuminated with oblique light, very fine fibrillae, 
lying parallel to each other, may be observed. Its inner 
surface is dotted with numerous nuclei of different diameters, 
similar to those of the white substance of the spinal marrow, 
but there is also a small number of others, which are spindle- 
shaped and probably belong to the connective tissue. 
It deserves to be mentioned here, that those large mother 
cells, packed with larger and smaller nuclei of a greenish 
lustre, and found, as described above, in the substance of the 
spinal marrow near the pia mater of a former period, are no 
longer met with. The multiplication of nuclei by the en- 
dogenous mode, has ceased; another mode, that by gemmation 
or budding, will henceforth be observed. 
In the sympathetic ganglia of this period, the formation of 
their peculiar ganglionic bodies has distinctly commenced. 
Although the greater portion of their nervous substance still 
consists of the same elementary forms, as found in the brain 
and spinal marrow, there are nevertheless a considerable num- 
ber of nuclei now met with, surrounded by a mass of granules, 
from which the rudimentary processes are seen to proceed in 
the form of granular filaments. Now, whether these fila- 
ments have already been connected with the granular nervous 
fibrillae, or whether this connection takes place subsequently, 
will be difficult to determine. I am inclined to think that it 
has existed'from the begi nning of the formation of the gan- 
glionic body. 
The sympathetic nerves still consist, like those of the 
cerebro-spinal axis, of bundles of granular fibrillae, each sur- 
rounded by a sheath. A number of oval nuclei are imbedded 
between the fibrillae. The sheath represents the neurilemma 432 
Schmidt—Development of the Nervous Tlstmes. 
and is derived from the membranous capsule, surrounding 
the whole sympathetic ganglion. 
In the spinal ganglia of this period, the development of the 
ganglionic bodies has still farther advanced, for they not only 
present all the characteristics of those of the thoracic ganglia, 
above described, but they have besides already assumed a more 
definite round or oval form. 
In reviewing the above observations, regarding the develop- 
ment of the nervous tissues, our attention cannot fail to be 
directed to quite an interesting fact, namely, that the develop- 
ment does not keep equal pace in all localities, but may be 
more advanced in one than in the other. Thus, while in the 
brain and spinal marrow we have so far only met traces of the 
formation of ganglionic bodies, we find them already formed 
in the sympathetic thoracic ganglia. And again we find the 
primary fibrilla1 of the nerve fibres in the peripheral nerves 
farther advanced in development, than in the spinal marrow 
or the brain. We shall refer again to this fact. 
After the embryonic period, thus far treated, in this paper, 
the nervous tissues commence to assume very gradually their 
later complicated structure, for which reason, we shall prefer 
to treat each tissue individually. 
In commencing with the nerves of the cerebro-spinal axis, 
in embryos of 15 ctm. to 15 ctin. in length,—about 
three and a half months old,—we find that each of them no 
longer consists of only a single bundle of nervous fibrillse, 
enclosed in the rudimentary neurilemma forming a single 
sheath; but that on the contrary, the fibrilke have subdivided 
into a number of bundles, each of which is surrounded by its 
own individual sheath of delicate connective tissue, which is 
derived from the neurilemma surrounding the whole nerve. 
Besides this, the fibrillae of each bundle have also commenced 
to separate themselves, either singly, or by tw'os, sometimes 
even by threes. The interspaces formed by this separation, 
are filled up with numerous nuclei of different diameters, and 
with granules. From the latter, new fibrilke are formed during 
the course of the development of the nerve. The nuclei, of 
course, are identical with those already described, between the 
granular fibrillse of a previous period. 
Somewhat later, in embryos, about 18 do ctm. long, and So11mii>t--Developifient of the Nervous Tissues. 
433 
four months old, the fibrillae forming the individual groups of 
two or three, have approached each other more closely and ad- 
here to each other. This phenomenon signifies the first step 
to the formation of axis cylinders. The interspaces‘formed, 
in consequence of this mutual approach of the fibrillae, have 
been rendered larger and more distinct. A number of these 
primitive axis cylinders, as already indicated before, consists 
of only one fibrilla. At the same time it is observed, that the 
smaller nuclei, lying in the interspaces, appear to become at- 
tached to the axis cylinders, in order to fuse with them, as we 
shall see directly. The rudimentary axis cylinders are difficult 
to separate from each other, which may be attributed to the ab- 
sence of the sheath, bv which they will somewhat later be 
surrounded; and also, because they’are imbedded together with 
the nuclei and granules, in an amorphous matrix of proto- 
plasm, which holds them together. 
Again, somewhat later, in the foetus of four and a half 
months, about 20 to 22 550 ct.m. in length, a number of prim- 
itive axis cylinders are observed to be surrounded each by a 
sheath of its own, which, when fully developed, is distinguish- 
able by a delicate double contour (Fig. 12). We must, however, 
remember, that all the axis cylinders of one bundle, do not 
keep equal pace in their development; on the contrary, while 
some of them may be already surrounded by their sheath, 
others may still be seen to lie bare, or the formation of the 
sheath may only be indicated by a delicate single contour. 
The nuclei, previously adhering to the axis cylinders, have 
now begun to fuse with them; they are also observed in differ- 
ent degrees of fusion. 
The next phenomenon in the development of the double 
contoured nerve fibre is the appearance of the nerve medulla, 
surrounding the axis cylinder, and manifesting itself by an 
extremely delicate single contour (Fig. 13, b). In some in- 
stances, however, traces of the formation of the tubular mem- 
brane, or external sheath* of this nerve fibre, may also be 
observed in the appearance of a second delicate contour, inside 
of the first. A few single granules are observed in the interior 
of the nerve fibre (Fig. 13, c). The diameter of the axis 
cylinder of this stage of development is not the same at all 434 
Schmidt—Development of the Nervous Tissues, 
points. In the vicinity of the nuclei fusing with the axis 
cylinders, it is usually greatest. The larger nuclei, which 
were previously observed to remain lying free and uncon- 
nected with the axis cylinders, are now found to rest upon the 
tubular membrane of the nerve fibre. 
Finally, about a month later, the double contoured nerve 
fibre is met with again, marked by all its peculiar characteris- 
tics. The tubular membrane, together with the fibrillar layer 
of the nerve medulla, manifest themselves now distinctly by 
their characteristic double contour. The delicate, smooth 
fibrillse of the fibrillar layer of the nerve medulla may now be 
seen in their wave-like course, crossing each other in the in- 
terior of the nerve fibre, or protruding in the form of loops 
from its torn ends, such as I have formerly described them* 
in the fully developed nerve fibre. The axis cylinder may also 
be seen in many instances protruding from the open end of 
the nerve fibre. It is only in the diameter, that the double 
contoured nerve fibre of this period of foetal life still differs 
from that of adult life, it being still smaller. 
The first distinct traces of the formation of ganglionic 
bodies in the spinal marrow, I observed in embryos measuring 
from 7 ,50 ct.ui. to 8 110 ct.m. in length, and about ten 
weeks old. The formation of these bodies takes place by a 
gradual accumulation of granules around one of the larger 
nuclei; from the granular mass fine processes are seen to arise, 
establishing a communication with the still granular nervous 
fibrillae of the future axis cylinder. The nucleus has as yet 
undergone no visible change in its character, for it still repre- 
sents a vesicle filled with granules, of which one or two of them, 
larger than the rest, may be regarded as nucleoli. I>y the 
continued attraction of fresh granules, the ganglionic body 
enlarges in circumference, and its processes in thickness and 
extension. 
Finally, in the spinal marrow of the foetus, about four and a 
half months old, a number of ganglionic bodies are observed, 
bordered by a delicate single contour, which in some instances 
even extends over their processes, and indicates the formation 
of the delicate sheath, enveloping the whole body, and being 
♦Monthly Microscop. Journal, May, 1874. Schmidt—Development of the Nervous Tissues. 
435 
continuous with the sheath of the axis cylinders arising from 
the processes (Figs. 14, 15, and 17). At the same time, how- 
ever, many of the ganglionic bodies have not yet passed the 
first stage of their development. But in the nucleus, also, a 
change has taken place. Its nucleolus, namely, having by this 
time gained considerably in its dimensions, shows a granule of 
a bright lustre in its centre. 
Still a month later, in the foetus of about five and a half to 
six months of age, the ganglionic bodies with their processes, 
besides having gained in volume, are now completely sur- 
rounded by their sheaths (Fig. 18). The interior of the 
nucleus is tilled with small granules of the same nature as 
those of the mass of the ganglionic body; its nucleolus has 
enlarged, and is seen more distinctly; the granule ill the 
centre has become brighter. Those accumulations of dark 
bordered pigment granules in the vicinity of the nucleus so 
characteristic of the ganglionic bodies of the nervous system 
of the adult, also have now made their appearance. Thus, all 
parts, characteristic of the ganglionic body, are now present, 
and, excepting its further development in volume, it appears 
but for one element to be near its completion. The missing 
part belongs to the nucleolus. In the fully developed gan- 
glionic body of the spinal marrow, the nucleolus is distin- 
guished bv a distinct double contour; its interior, besides 
being tilled by small granules, contains one or two clear bodies 
of a reddish lustre. One of these, being always present, is 
also distinguished by a double contour, and shows, besides 
this, a dark granule in its centre. The fully developed 
nucleolus of the ganglionic body, therefore, is quite a com- 
plex body, for which reason, on a former occasion, I assigned 
to it the character of a nucleus, and regarded the so-called 
nucleus as the true nerve, cell. The nucleolus of the gan- 
glionic bodies of the spinal marrow of the foetus under discus- 
sion, on the contrary, shows only a single contour, and the sole 
object it contains is the bright granule, which, however, is not 
as yet distinguished by a double contour, nor does it contain a 
dark granule in its centre. 
In consideration of the fact, therefore, that the nucleolus is 
that part of the ganglionic body, which, last of all others, 436 
Schmidt—Development of the Nervous Tissue. 
attains its perfection, we cannot but suspect, that its office in 
the function of the ganglionic body must be an important one. 
The ganglionic bodies of the cortical layer of the brain ap- 
pear to attain their full development somewhat later than 
those of the spinal marrow, or even those of the medulla ob- 
longata, or the larger cerebral ganglia, the corpora striata, etc. 
In the earlier periods of embryonic life, we have met only 
their first traces in the form of a few nuclei, to which some 
short granular fibrillse were adhering. The first distinct traces 
I observed in embryos, measuring about 15 or 17j50 centi- 
metres in length. The brain, at this period, from the third to 
the fourth month, still consists, in its greater part, of the 
granular substance and those nuclei already described before. 
A considerable portion of the granules, of course, are now 
arranged into rows. The force, however, which binds them 
to each other is still very feeble, so that they become very 
easily deranged and disconnected, even under the most deli- 
cate manipulation. Amidst these elements, a small number 
of ganglionic bodies are observed in different stages of devel- 
opment,. Though, in those specimens, furthest developed, the 
granular mass completely embraces the nucleus; the processes 
proceeding from it are still short; they are usually from three 
to four in number (Fig. 16). As has already l>een remarked, 
in connection with the spinal marrow, those mother-cells 
filled with nuclei of a greenish lustre, and found in the matter 
of the brain and spinal marrow of an earlier embryonic pe- 
riod (Figs. 7 and 9), and serving for the multiplication of 
nuclei, are seen no more. The multiplication of these bodies 
is now accomplished by another mode, namely, by the process 
of budding, or germination. Thus, instead of those large 
mother-cells, we observe a number of nuclei of a greenish tint, 
provided with small, clear vesicles, which become ultimately 
detached, in order to be transformed into nuclei themselves 
(Figs. 16 and 24). A number of nuclei are also observed bear- 
ing one or more spherical depressions, the remaining traces of 
former vesicles. This mode of multiplication of nuclei, 1 
described some time ago, in connection with the development 
of the smaller blood vessels in the human embryo.* 
* Monthly Microscop. Journal, January, 1875. Schmidt—Development of the Nervous Tissues. 
437 
Let us pass over now to a period of foetal life, when the 
brain has attained such a degree of development, as to possess 
sufficient consistency to allow, after having been hardened in 
a weak solution of chromic acid, of making transparent sec- 
tions, the only mode of preparation, which admits of an exact 
examination. In examining such a section of the cortical 
layer of the cerebrum of a foetus, seven months old, we find 
the nervous elements, composing this layer, already arranged 
in regular order (Fig. 19). The ganglionic bodies have now 
assumed their later pyramidal form, their long-pointed pro- 
cesses can be distinctly seen stretching toward the surface of 
brain, also their lateral and local processes, pursuing their 
course laterally or downward toward the white substance. In 
some instances, even, I have observed a primitive axis cylinder 
in the form of granular fibrillse. arising from one of the latter 
processes. A considerable number of granular fibrillse are 
seen running vertically from the surface toward the white 
substance. They represent the future double-contoured nerve 
fibres. Numerous free nuclei, distributed between the gangli- 
onic bodies, are seen imbedded in the granular substance. 
But the most interesting of all these parts, composing the 
cortical layer, is the fine terminal network of nervous fibrillse, 
distinctly seen to extend throughout this substance. We see, 
therefore, that although these anatomical elements of the cor- 
tical layer of the cerebrum are not fully developed, they are, 
nevertheless, already arranged in perfect order, and we must 
not be surprised to see a foetus, born at the end of the seventh 
month, live without detriment to the development of his men- 
tal faculties. 
In the newly-born child, finally, we find the mental appa- 
ratus almost fully developed (Fig. 20). The ganglionic 
bodies have nearly obtained their full growth and structure. 
In some of them, the characteristic collections of dark-bor- 
dered pigment granules have also made their appearance. 
The rudimentary axis cylinder, which, in the foetal brain of 
seven months, we observed arising from the basal processes of 
the ganglionic bodies, and pursuing their course toward the 
white substance, have now been developed into double con- 
toured nerve-fibres. Nevertheless, some of the granular fibril- 
lae are still noticed among these fully developed fibres; and 438 
Schmidt—Development of the Nervous Tissues. 
I doubt not, but that the development of new axis cylinders 
continues as long as new ganglionic bodies are formed. In 
fact, it would be an interesting question to solve, until what 
time of life this last process goes on. Among the free nuclei, 
embedded in the granular substance of the cortical layer of 
the brain under discussion, I have several times observed two 
nuclei, overlaping each other, suggesting the question, whether 
they do not owe their origin to the division of one nucleus. 
Finally, the terminal net work of nervous fibrillse is now as 
distinctly seen as in the adult brain; and, moreover, the tine 
branches of the long pointed process are observed to lose 
themselves in its meshes. 
We have now arrived at the most difficult part of our sub- 
ject, the study of the development of the sympathetic gangli- 
onic bodies. The structure of these bodies has always been 
one of the most obscure subjects in histology, and hence the 
discrepancies, which have arisen concerning it, in the views 
and statements of different investigators. The chief difficulty 
in the examination concerns the characteristic capsule, which 
incloses the ganglionic body of the sympathetic nervous sys- 
tem and its relation to, and its connection with this body. 
Therefore, before giving a description of their development, 
I deem it necessary to recall to mind the structure of the fully 
developed sympathetic ganglionic body, as I have described 
it. According to my investigation,* the sympathetic gangli- 
onic body, which is generally round in form, consists of a 
large nucleus, surrounded by a mass of granules. From this 
mass, a number of larger and smaller processes are seen to 
arise; the whole enclosed in that peculiar membraneous 
capsule. The larger processes, from one to four in number, 
after arising from the body, pierce the capsule, and disappear 
in the form of naked axis cylinders, at a distance of about 
ylhj- mm. or more, among the neighboring bundles of sym- 
pathetic nerve fibres. What becomes of them is not certainly 
known, but I have reason to believe, that they are finally 
transformed into dark-bordered nerve fibres. The smaller 
processes, arising from the body, are more numerous than the 
former, and consist mostly of only two or even one fibrilla. 
After a short course alongside of the body, they enter the 
* Transactions of the American Neurol. Assoc’n, 1865, p. 107. Schmidt—Development of the Nervous Tissues. 
439 
capsule at its inner surface, and form, by means of ramification 
and reciprocal connection, a network extending throughout 
this membrane; the interspaces of the network are tilled up 
by small granules. The capsule of the sympathetic gangli- 
onic body, therefore, represents a complicated membrani- 
form, nervous structure, derived from and connected with the 
body, which it encloses. On the surface of the capsule, 
formed in this manner, a number of fine fibrillae arise from 
the network, a part of which pass, in the form of a finely 
reticulated plexus, over into the capsules of neighboring 
ganglionic bodies, and thus establish a reciprocal communica- 
tion; the rest surround the axis cylinders arising from the 
larger processes and having pierced the capsule, and running 
in the same direction with these, unite among themselves to 
form finally the so-called sympathetic nerve fibres. Scattered 
over the inner as well as the outer surface of the capsule, a 
considerable number of round or oval nuclei are observed. 
They are especially numerous in the reticulated fibrillous 
plexus, connecting the ganglionic bodies with each other, 
whence they extend, while assuming a more oblong form, be- 
tween the sympathetic nerve fibres. 
As we have already seen in the preceding pages, there ex- 
ists no essential difference in the formation of the primary 
ganglionic bodies of the cerebro-spinal axis and those of the 
sympathetic ganglia. They are all formed by an aggregation 
of granules around a pre-existing nucleus; from this granular 
mass, the processes arise, to be subsequently connected with 
the primitive nervous fibrillae. While, however, the cerebro- 
spinal ganglionic bodies attain their full development in this 
manner, those of the sympathetic system, must deviate from 
it, in order to form their characteristic capsule. 
In embryos of 5 T6ff to 5 T9F ctm. in length we find the 
ganglionic bodies of the thoracic ganglia, as already mentioned, 
to consist of a nucleus, only surrounded by one or two layers 
of granules from which a few filamentous processes are seen 
to arise. These primary ganglionic bodies are embedded in the 
general mass of granules and nuclei, of which at this time the 
greater part of the ganglion still consists. A considerable por- 
tion of the granules, however, are arranged into rows, repre- 
senting primitive nervous fibrillar. In fact, this was already  Schmidt—Development of the Nervous Tissues. 
440 
the case to some extent, as will be remembered, in the spinal 
ganglion of an embryo, only 16 mm. in length. But the ad- 
hesion of the granules is still too feeble, to prevent them from 
being deranged by the most delicate manipulation. It is for 
this reason, that the filamentous processes are always found to 
be torn (Fig 21). In the spinal ganglia of the same embryo, 
however, the development of their ganglionic bodies is found 
to be considerably in advance of those of the thoracic ganglia. 
Not only have these bodies assumed a more definite form and 
gained in size; but they are already attached to each other bjr 
filamentous processes, forming small groups, as later in life, 
when they are fully developed (Fig. 22). Other bundles of 
fibrillae are seen to arrive from them, uniting to form the 
sympathetic nerve fibres. It will be noticed, however, that 
there are, as yet, no nuclei attached to any of the nervous 
fibrillae. In my previous descriptions of the structure of the 
sympathetic ganglionic bodies, 1 said, that I suspected their 
larger axis cylinder processes would be ultimately transformed 
into a dark-bordered nerve fibre. But in taking into consider- 
ation the reciprocal connection of these bodies by their larger 
processes, as seen in Fig 22, it may be possible also, that by 
means of these processes, the destination of which is still un- 
known, a reciprocal connection is established between the 
ganglionic bodies of one and the same group. 
Now, in examining a small group of ganglionic bodies of 
the spinal ganglion of an embryo, 10 T®0 ctm. in length, and 
about eleven to twelve weeks old, we behold the first traces of 
the formation of the capsule. It will be noticed here (Fig. 23), 
that some of the filamentous processes have become attached 
to the nuclei, lying between the ganglionic bodies. In the 
preparation, a number of processes have been torn from the 
bodies by the manipulation. 
A few weeks later, in the embryo of about four months, 
and 17t50 ctm. in length, the formation of the capsule is 
seen more distinctly. The fine filamentous branches arising 
from a number of the processes of the ganglionic bodies, have 
now commenced to unite with each other, in order to form the 
filamentous network of the capsule. At the same time, they 
are observed to adhere to the numerous nuclei, surrounding 
the ganglionic bodies. Schmidt—Development of the Nervous Tissues. 
441 
Fig. 24, a, represents a ganglionic body of a thoracic gan- 
glion of this embryo; it illustrates the formation of the cap- 
sule better, than it can be described, for it shows distinctly 
the ramifications of the processes, the communication of the 
filaments in forming the meshes of the network, and their at- 
tachment to the nuclei. In S, of the same figure, we behold 
some of the nuclei, entangled in the filamentous mass found 
between the ganglionic bodies. 
Tn Fig. 25, which represents a ganglionic body of a spinal 
ganglion of the same embryo, the formation of the network of 
the capsule is still more distinctly seen. 
In studying the formation of the capsules of the sympa- 
thetic ganglionic bodies on the preparations just described, it 
must be remembered that they have been made by separating 
the component anatomical parts of minute portions of a gan- 
glion, with finely pointed needles, and that it is impossible to 
avoid tearing and displacing some of these parts. It is for 
this reason, that we do not see the anastomosing nervous fila- 
ments with their nuclei surrounding the ganglionic body 
while forming the rudimentary capsule, but observe them only 
attached to the processes of the body. In the foetus of six 
and a half months of age, however, the first cervical sympa- 
thetic ganglion has attained a sufficient size to allow thin 
transparent sections to be made, after it has been hardened in 
a weak solution of chromic acid. 
Such a section we find represented in Figs. 26 and 27. In 
examining Fig. 26, we observe three capsules, cut at one and 
the same level. The ganglionic bodies, being exposed by the 
section, are seen in the interior of the capsules. While in the 
fresh specimen, however, the ganglionic body nearly fills the 
interior of the capsule, we find in this instance the granular 
mass of the body considerably contracted by the action of the 
chromic acid. The processes which, in consequence of this 
contraction, have to a certain degree been put on the stretch, 
appear somewdiat larger; they are subdividing, and the branches 
resulting from this subdivision are seen ramifying throughout 
the wrall of the capsule, forming the network. From the outer 
surface of the different capsules, small bundles of nervous 
fibrillae are seen to arise, joining with each other in their course 
in order to form larger nerve bundles. This preparation also 442 
Schmidt—Development of the Nervoux Tissues. 
shows how the component anatomical elements of‘ adjoining 
capsules run into each other. The nuclei are seen dispersed in 
the capsules and in the reticulated plexus, arising from these. 
In examining this preparation, it must he remembered, that a 
number of the smaller processes have been torn off by the knife 
in making the section, and furthermore, that the structure of 
the capsule has, as yet, not attained its perfection. 
In Fig. 27, which was copied from the same section, we see 
the outer surface of a capsule. The network or plexus, formed 
by the nervous fibrillae, derived from the ramifications of the 
smaller processes of the ganglionic body, is here very dis- 
tinctly exhibited, and, moreover, small bundles of fibrillse may 
be observed arising from it, to finally join a neighboring bun- 
dle of nerve fibres. 
In making a final review of the facts elicited by these inves- 
tigations into the development of the nervous tissues, de- 
scribed in the preceeding pages, we first notice, that these tis- 
sues are not developed in the true sense of the word from pre- 
existing cells, as was formerly supposed, but, on the contrary, 
are developed by the aggregation ot pre-existing minute gran- 
ules, which either collect around a pre-existing nucleus, as in 
the formation of the ganglionic bodies; or arrange themselves 
into rows, as in the formation of the fibrillse of the axis cylin- 
ders. 
The principal anatomical elements, then, taking part in the 
formation of the nervous tissues, are a mass of pre-existing 
minute granules with a special material binding them to each 
other,—the intermediate substance, as I have occasionally 
called it,—and a large number of pre-existing nuclei. The 
granules, together with the intermediate substance, may he 
regarded as the protoplasm of these primitive formations. 
Nevertheless, in more minutely comparing the development 
of an organic cell with that of the nervous tissues, we cannot 
fail to recognize a certain analogy between the two processes. 
This exists in the formation of the wall in the one instance, 
and the formation of the sheath of the axis cylinder, as well as 
that of the jnuml ionic bodv in the other instance. As the 
wall of the cell, namely, is formed by a condensation of the 
protoplasm, taking place at its surface, so, I believe, the sheath 
of the axis cylinder and that of the ganglionic body, are Schmidt—Development of the Nervous Tissues. 
443 
formed by a condensation of the intermediate substance, which 
not only connects the individual granules of the nervous fi- 
brillae with each other, but also surrounds the fibrillse them- 
selves. Thus the ganglionic bodies of the nervous system 
may still be regarded in the light of organic cells, which, mul- 
tipolar in form, would send the ramifications of their processes, 
in the form of nervous filirillae, to the various peripheral or- 
gans. 
The view has been held, and perhaps still is, by some an- 
atomists, that the great nerve centres, the brain and spinal 
marrow, were the first parts of the nervous system formed, and 
that the nerves, regarded as simple processes, or prolongations 
arising from these centres, were growing outwardly into the 
tissues, finally to arrive at the periphery. In the preceding 
pages it has been shown, that this is by no means the case, 
but, on the contrary, that the peripheral nerve fibres are sooner 
developed than those of the centre; and, furthermore, that the 
nerve fibres arrive at their full development sooner, than the 
ganglionic bodies. As regards the tissues of the different 
parts of the nervous system, we find that they attain their full 
development first in the sympathetic ganglia, especially in the 
spinal; next in the spinal marrow, and last in the brain. 
This order of development might he expected, for it truly 
corresponds with the different grades of functions, namely, the 
vegetable, animal and mental. 
EXPLANATION OF PLATES. 
Fig. 1.—Human embryo, 0 mm. in length; nat. size. 
Fig. 2.—Human embryo, 9 mm. in length, nat. size; «, anterior, b, 
lateral and c, posterior view. 
Fig. 3.—Human embryo of 16 mm. in length. 
Fig. 4.—Elementary forms of striated muscular fibres, from the upper 
extremities of the embryo, represented in Fig. 3. 
Fig. 5.—Primary muscular fibre from the tongue of the same embryo, 
with its fibrillae separated from each other. 
Fig. 6.—Spindle shaped bodies (cells) of the primary muscular fibre of 
the auricles of the heart of the same embryo. 
Fig. 7.—Primary anatomical elements of the brain of embryo, Fig. 2; 
a, nuclei and granules; b, mother cells, containing a brood of nuclei; c, 
primar}' elements of blood vessels. « 
Fig. 8.—Nervous matter of the brain of embryo, Fig. 3; a, white sub- 
stance; b, grey substance; c, nuclei with nervous filaments adhering to 
them; d, different forms of clear mother cells, described in the text. 444 
Schmidt—Development of the Nervous Tissues. 
Fig. 9.—a, minute portion of the pia mater of embryo, Fig. 3, with nerv- 
ous matter adhering; b, groups of clear mother cells: e large mother cells, 
containing a brood of nuclei of a greenish lustre. 
Fig. 10—Minute portion of spinal marrow from embryo, Fig. 3, show- 
ing the formation of nervous fiibrillse. 
Fig. 11.—Bundle of nervous fibrillae from the brachial plexus of an em- 
bryo, about nine weeks old. 
Fig. 12.—Nervous bundle from the root of a spinal nerve of an embryo, 
three and a half months old; it illustrates the formation of the axis cylin- 
ders. 
Fig. 13.—Nerve fibres from the brachial plexus of the same embryo, 
showing the formation of the nerve medulla and the tubular membrane; 
a, primitive axis cylinder; b, nerve fibre with single contour; c, nerve 
fibre with double contour. 
Fig. 14.—Minute portion of gray substance from the upper part of the 
spinal marrow of an embryo, three anda half months old, showing the 
formation of ganglionic bodies. 
Fig. 15.—Ganglionic body from the dorsal region of the spinal marrow 
of the same embryo. 
Fig. 16.—Nervous matter from the brain of a foetus, four mouths old, 
showing the formation of ganglionic bodies, and the process of multipli- 
cation of nuclei by germination. 
Fig. 17.—Communicating ganglionic bodies from the spinal marrow of 
the same foetus. 
Fig. 18.—Minute portion of spinal marrow of a foetus four and a half 
months old. 
Fig. 19.—Thin transparent section of the cortical layer of the cerebrum 
of a foetus seven months old. 
Fio. 20.—Thin section of the same layer of the cerebrum of a fietus at 
full term. 
Fig. 21.—Ganglionic bodies from a thoracic sympathetic ganglion of 
an embryo, about nine weeks old. 
Fig. 22.—Group of sympathetic ganglionic bodies from a spinal gan- 
glion of the same embryo. 
Fig. 23.—Group of sympathetic ganglionic bodies from spinal ganglion 
of an embryo, from eleven to twelve weeks old. 
Fig. 24.—o, sympathetic ganglionic body from the thoracic ganglion of 
an embryo of four months, showing the formation of its capsule; b, nuclei, 
entangled in nervous fibrillae during the formation of the capsule. 
Fig. 25.—Sympathetic ganglionic body from a spinal ganglion of the 
same embryo, also illustrating the formation of the capsule. 
Fig. 26.—Thin transparent section of the first cervical sympathetic gan- 
glion of a foetus six and a half months old, showing the structure of the 
capsule. 
Fig. 27.—External surface of a capsule, showing the network or plexus 
of nervous fi brillae, also the bundles of fibrillae arising from it, and joining 
a neighbouring nerve bundle. 
The above figures are magnified 420 diameters, with the exception of the 
first three.