Paper - Prenatal growth of the human spinal cord

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Miller MM. Prenatal growth of the human spinal cord. (1913) J. Comp. Neurol. 23(1): 39-70.

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This historic 1913 paper by Miller described development of the human spinal cord.



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Prenatal Growth of the Human Spinal Cord

Max Mayo Miller

From The Anatomical Laboratory, University Of Missouri

Twelve Figures

Introduction

In‘human embryology the changes in form and the histological differentiation in the cellular elements of the spinal cord have been studied very carefully. But as yet little has been done on the absolute and relative prenatal growth of the cord as a whole and of its various regions and parts. To throw light upon this matter the present study was undertaken. The data here presented include: First, the absolute and relative growth of the spinal cord in its entirety; second, the absolute and relative amounts and the rate of growth of the different regions of the cord; and third, the absolute and relative amounts and the rate of growth of the gray matter, of the white matter and of the ependyma with the canal. This investigation was carried on in the Anatomical Laboratory of the University of Missouri, under the direction of Prof. C. M. Jackson, to whom I am also indebted for the use of his collection of human embryos.

Material and Methods

The material used consisted of the following embryos: 11 mm. (No. 60, fifth week), 17 mm. (No. 58, sixth week), 31 mm. (No. 57, eighth week), 65 mm. (No. 55, twelfth week), and 150 mm. (No. 54, five months). The lengths are all crown—rump measurements. The ages are only approximate and all conclusions referring to them are, therefore, subject to more or less uncertainty.


The embryos had been prepared by the following methods: No. 60 (9?) was fixed and hardened in alcohol, stained in bulk in alum-cochineal, embedded in parafiin, and cut into transverse serial sections, 20 u thick. No. 58 (9) was fixed in formalin, hardened in alcohol, decalcified in acid-alcohol, stained in bulk in alum-cochineal, embedded in paraffin, and cut into transverse serial sections, 20 [L thick. No. 57 (9) was fixed in formalin hardened in alcohol, decalcified in acid-alcohol, stained in bulk in alum-cochineal, embedded in paraflin, and cut into transverse serial sections, 20 p thick. No. 55 (6') was fixed in formalin, hardened in alcohol, decalcified in 1 per cent HCl in 70 per cent alcohol, stained in bulk in alum-cochineal, embedded in paraffin, and cut into transverse serial sections, 50 p thick. No. 54 (9) was fixed in formalin, decalcified in 2 per cent nitric acid in 70 per cent alcohol, embedded in celloidin, cut into transverse serial sections, 100 p thick, and stained with alum-haematoxylin. This material is all in good condition, especially the younger embryos.

Sections of these embryos were magnified by means of an Edinger projection apparatus (E. Leitz—Wetzlar) and outline drawings made of cross-sections of the spinal cords. In the case of the 11 mm., 17 mm., 31 mm., and 65 mm. embryos, every fourth section was drawn, while in the embryo of 150 mm. only every tenth section was used. In exceptional cases where the section to be drawn Was torn or distorted, the adjacent section was drawn instead. The magnification used was 50 diameters, which corresponds to a magnification of 2500 times in cross-sectional area.


The areas of these drawings were measured with a planimeter (Coradi). This instrument on being tested showed an error of less than 0.25 per cent. Two entirely independent readings were made in each case and the average used in order to minimize the error. The percentages of the gray matter (anterior and posterior horns), of the white matter (anterior, lateral, and posterior columns), and of the ependyma with the canal were first calculated from the original readings. The original readings were then reduced to their actual size from which again the percentages of the various parts were calculated. This gave a check on the accuracy of the calculation. Since the thickness of the sections was known, it was easy to calculate the total volumes of the cords and their various parts.


The first section which showed filaments of the first pair of spinal ‘nerves was taken as the upper level of the spinal cord. This, however, was not always the exact upper level, on account of the obliquity of the section caused by the normal curvature of the younger embryos. This error is in most cases not large enough to interfere seriously with the general results, but should be borne in mind.


The length of a segment was determined by taking all sections between the uppermost point of attachment of a nerve to the cord and the corresponding point of the next pair of nerves caudal to the first. Since the thickness of the sections was lmown, the lengths and volumes of the various segments were readily calculated. Owing to the curvature of the younger embryos 1t was impossible in these to obtain the exact length of the upper and the lower segments. This, however, did not interfere with obtaining accurately the total volume of the cord and of the various regions. In the 65 mm. and 150 mm. embryos the uppermost segments were missing. These were estimated by calculation from the other segments of the same cords, assuming that the same relative increase takes place in these segments as in the other segments of the same cord, when compared with the cord of the 31 mm. embryo. While the obliquity of some of the sections interfered in some respects, these exceptions are carefully noted so that they have not resulted in any great error in the accuracy of the work. The curvature and corresponding obliquity of cross-sections can be determined approximately by the graphic reconstruction in lateral view of the four younger embryos in the paper by Jackson (’09 a).


The exact line of demarcation of gray from White matter was sometimes difiicult to determine, due to their intermingling. In the younger embryos in which only the anlages of the anterior and posterior horns are present, a horizontal line was drawn from the small recess in the boundary zone of the gray matter, which was very thin, to the nearest point of the central canal. This line arbitrarily separated the anterior from the posterior horns. The lateral horn was not present in the younger embryos. In the older stages the lateral horn was included With the anterior, thus dividing the gray matter into a posterior and an antero-lateral horn (figs. 1 to 5).


The white matter was separated into the anterior, posterior, and lateral columns. The lateral border of the anterior column is the line of emergence of the outermost fascicles of the nerve roots. This separates the anterior and lateral columns. The dorso-lateral sulcus at the attachment of the posterior nerve roots separates the posterior and lateral columns. In the 11 mm. specimen the lateral columns showed such an irregularity that they Were not separated but measured With the anterior columns. For exact lines of demarcation, see figures 1 to 5.

Observations and Discussion

A. Cord as a Whole

1. General form of the prenatal spinal cord

(figs 1 to 12; tables 2 to 6)

The spinal cord in the human embryos studied shows various points of resemblance in form to the cord in the adult, as shown in figures 6 to 12. Passing caudad from the brain there are indications, however, that the embryonic spinal cord diminishes gradually in its diameters to about the region of the 3rd cervical segment. This resembles the cord of the child (Stilling), but not of the adult. From here there is in the embryonic cord a slight but constant increase in caliber, which reaches its maximum in the region of the 4th or 5th cervical segment. This enlargement in the cervical region corresponds to the intumescentia cervicalis. This is followed by a more gradual decrease in area of cross-section, which usually extends to about the 3rd or 4th thoracic segment. The thoracic segments, from the 3rd to the 8th, have practically the same area of cross-section in each of the embryos examined. This is also true in the child, but to a less extent in the adult. Near the lower end of the thoracic region there are indications of the intumescentia lumbalis. The cord in general increases in area of cross—section from the lower thoracic segments to the 5th lumbar segment or thereabout, whence there is a gradual tapering of the cord as it decreases in cross-sectional area to its end in the filum terminale. The lower ends of the cords are, therefore, somewhat conical in shape.

In general shape the prenatal cord in cross-section is at first oval, being compressed in its transverse diameter (figs. 1 to 5). Later, however, it becomes compressed in the dorso-ventral diameter and expanded laterally. In the thoracic region, the spinal cord more nearly retains a cylindrical form. In these respects the later fetal cord approaches the postnatal condition. If we compare the increase in cross-sectional area at successive stages with the increase in volume of the spinal cord, we find in general that the volume increases more rapidly. That is, the cord becomes relatively longer and slenderer during the prenatal life, and this tendency continues in the child to the adult.

2. Special features in the various embryos

(figs. 1 to 12; tables 2 to 6)

In the 11 mm. embryo only the cervical and thoracic segments were measured separately. By referring to table 2 and figure 6, one can readily see that this embryo diflers somewhat from the preceding general description. Owing to the obliquity of the section in the cervical and lower thoracic regions (due to the normal curvature of the spinal cord in embryos of this length), not much stress can be laid on the apparent increase in area of cross-section in these regions as shown in the curve. However, from measurements of the transverse diameters (which are not affected by the obliquity) of these sections, which show an increase in the cervical region, the indications are that there is a slight expansion in the region of the cervical enlargement. There is, however, no evident lumbar enlargement. The apparent increase shown in the curve in the lower thoracic region is probably due entirely to the obliquity of the sections. Excepting the slight cervical enlargement, the cord seems to taper from the cephalic end to the caudal extremity. The lower end of the cord is so curved that the segments could not be separated. The shape of the cord in cross-section (figs. 1 a and 1 b) is in general like that of a rectangle with the corners rounded. The outline is not smooth, due probably to the fact that the columns of white matter are as yet not formed.


The spinal cord of the 17 mm. embryo presents (as shown in table 3, figs. 2 a and 2 b, and fig. 7) some of the same features as the cord of the 11 mm. specimen. From the increase in areas of cross-section and in the transverse diameters of the sections, it is evident that there is in this cord a noticeable increase in the region of the cervical enlargement, and a very slight increase in the lower thoracic and upper lumbar segments which is possibly due in part to the beginning of the lumbar enlargement. The actual increases both in the cervical and thoraco-lumbar regions are less than those apparently shown on the curve, due to the curvature of the cord and the corresponding obliquity of the sections.


In the 31 mm. embryo (table 4, figs. 3 a, 3 b, and 3 c, and fig. 8) the upper three segments are so cut as to contain both medulla and spinal cord. The outline of the cord could be measured separately, however. The cervical enlargement is recognizable also in this cord. This is the youngest embryo in which there is a wellmarked lumbar enlargement. This does not agree with Bryce (’08) who states that the cervical and lumbar enlargements are only manifest at the end of the third month. However, Streeter (’11) finds indications of the enlargements at the end of the first month, while Minot (’92) states that they occur at two months (well developed at three months). The cord of the 31 mm. embryo is but slightly larger in area of cross-section (and even smaller in places) than that of the 17 mm. specimen. The difference may be due in part to individual variation and in part to the growth being chiefly along the longitudinal axis about this period.


The upper two cervical segments in the 65 mm. embryo (table 5 and fig. 9) are lacking. They were estimated to complete the data. - This was done by assuming that these segments would show the. same relative increase as other segments of the same cord, when compared with corresponding segments of the cord in the 31 mm. specimen. They are enclosed in parentheses in the table. A marked variation occurs in this cord. The cervical enlargement appears relatively small. The lumbar enlargement showsa greater area of cross—section than the cervical enlargement. As this relation is not found in any other cord examined, it is due either to more rapid relative growth of the lower portion of the cord at this period or (more probably) to an individual variation. The tapering of the lower extremity of the cord is completely shown here, since all the lower segments were measured separately in this specimen.


In the cord at the middle of the prenatal period (150 mm.: table 6 and fig 10) the upper three cervical segments are missing. These were estimated as above. This cord agrees well with the general description previously given.

3. Growth of the cord as a whole

The total volumes of the spinal cords measured are shown in table 1. From these data and volumes of the entire body (Which were known) the percentages that the cords bear to the entire body were calculated. They are as follows:

++++++++Table++++++++

I C. B. LENGTH OF‘

Emmyo non! vommm voumm or smzun conn % or 1-01-.u. non! vontnm mm. cc. cc. per cent 11 0.976 0.004024 4.130 (4.85) 17 0.3788 0.01194 3.150 (3 . 43) 31 1.6930 0.02115 l . 250 (1.53) 65 (20.00)1 0.1505 0.755 150 (200.00)1 0.3969 0.198

1 Estimated

+++++++++++++++++++++++++++++++++

The diflerence in the percentages obtained by Bonnot and Seevers (’06) for the 11 mm., and Jackson (’O9 b) for the 17 mm. and 31 mm. specimens, and those by myself is quite marked. Their results are given in parentheses, and are larger in every case. This difference is due chiefly to a difference in technique. In measuring the area of the various sections they took the border on the outer edge of the meninges immediately surrounding the cord, and passed directly over the anterior fissure and posterior sulcus, while I in all cases measured on the surface of the spinal cord proper, leaving out, the meninges and following the various breaks in the continuity of the outline. A small difference would be expected due to this difference in technique.

The absolute growth of the prenatal cord is Very rapid in the younger embryos as shown by the total volumes of the cords in table 1. This is What is expected, since the neural tube or anlage of the spinal cord develops very early in the embryo. The rate of growth seems, in general, to decrease with the age of the embryo. During the second and third months (11 mm. to 65 mm.), the cord has increased thirty-six times, or 3600 per cent. In the fourth and fifth months (65 mm. to 150 mm.) together the increase is only approximately 160 per cent.

The decrease in the relative growth-rate with age is also shown by the decline in the percentage which the spinal cord forms of the entire body. This agrees with the rate of absolute growth in that as the age increases the percentage becomes relatively smaller. Vierordt ('06) gives 0.18 per cent of the total body weight for the spinal cord in the newborn and 0.06 per cent in the adult. These figures added to my results show that the decrease in growth-rate of the spinal cord continues through prenatal into postnatal life. This agrees with the conclusion reached by Jackson (’09 b).

4. Growth of the various regions

a. Cervical region. The diflerent regions in the spinal cord show in their rates of growth some slight diflerences when compared with the rate of growth of the entirercord. The cervical region exhibits a slower rate of growth than the whole cord up to the 31 mm. embryo, while from here to the end of the first half of prenatal life (150 mm. embryo) it slightly exceeds the growth rate of the whole cord. The cervical region during this time increases approximately 175 per cent, while the entire cord during the same period increases less than 166 per cent.


The relative amounts by volume which the diflerent regions form of the entire cord are given in table 1. The cervical region in the 11 mm. embryo constitutes 37 per cent of the entire cord. This is probably somewhat too large owing to the obliquity of the cord in this region. There is a slight decrease to about 28 per cent in the mid-fetal cord (150 mm.). In the two-year-old child it is relatively larger, forming 36 per cent of the entire cord. There is a decrease to 31 per cent between this and the adult stage, which seems to correspond to the increase in the thoracic region of the cord.


In area of cross-section, using the 5th cervical segment for comparing the growth of the cervical region, it is observed (tables 3 to 6, also figs. 1 to 12) that the area increases as growth in volume proceeds. However, a comparison of the 17 mm. and 31 mm. embryos shows that the cross-sectional area increases only about 60 per cent while the volume in the same period increases over per cent. This indicates that during this period the growth along the longitudinal axis is greater than in the transverse diameters. The 65 mm. embryo in cross-sectional area shows a small absolute decrease over the 31 mm. embryo in the cervical region. This decrease is probably due to individual variation. During the latter part of the first half of prenatal life the relative growth in area of cross-section continues relatively less than the growth in volume, as compared with the younger stages. By using the areas of the cross-sections of the 5th cervical segment as given by Donaldson and Davis ('03) (taken from Stilling) for a child of two years and a composite adult, an increase of 600 per cent occurs in the child, as compared with the 150 mm. embryo and of only 100 per cent between the child and the adult.


b. Thoracic region. The thoracic region in volume shows an increase of slightly less than 400 per cent between the 11 mm. embryo and the 65 mm. specimen. This is more than the increase in the cervical region during the same time, which is less than 300 per cent. As a result, the thoracic region, which is smaller than the cervical region in the 11 mm. embryo surpasses it in the 17 mm. embryo. From the 65 mm. embryo to the midfetal period (150 mm.), the thoracic continues to increase slightly more rapidly than the cervical region. This is also true for the thoracic region when compared with the cord as a whole, as shown in table 1. The thoracic region of the cord continues to increase relatively through postnatal life, forming 50 per cent of the adult cord, while the cervical forms only 31 per cent.


In cross-sectional area the thoracic segments from the 3rd to the 8th are practically constant. The relatively slight increase in cross-sectional area from the 17 mm. to the 65 mm. specimens (tables 3 to 5) is in agreement with the previous statement that during this period the growth is greatest along the longitudinal axis. The cord of the 31 mm. embryo is even slightly smaller in cross-sectional area than that of the 17 mm. embryo in the thoracic region. This absolute decrease is probably due to an individual variation. By using data for the child and adult, taken from Donaldson and Davis (’03) and Stilling (’59) it is shown that in the time which elapses between the mid-fetal period and the second year of postnatal life the cross-sectional area of the thoracic region increases approximately 1000 per cent, while from here to the adult there is an increase of only about 100 per cent.


c. Lumbo-sacral region. The lumbo—sacral region of the spinal cord shows (table 1) approximately the same rate of growth in volume as the thoracic region and a faster one than the cervical region up to the 17 mm. embryo. The lumbo-sacral region forms 31 per cent of the entire cord in the 11 mm. embryo. It increases relatively until in the 31 mm. specimen, it comprises 38 per cent of the Whole cord. The lumbo-sacral region decreases in relative size in later prenatal life until in the child and in the adult it forms only 18 per cent of the entire cord. The sacral region decreases relatively more than the lumbar. After they can be difierentiated (31 mm.) the lumbar region is about seventeen times as large as the sacral. In the child, however, the lumbar region is twice as large as the sacral, and in the adult nearly four times as great.


The 4th lumbar segment is used to compare the areas of crosssection in the lumbar region (figs. 1 to 5). In the younger embryos (11 mm. and 17 mm.) this segment could not be measured owing to the curvature of the cord. In the 65 mm. embryo the cross-sectional area of the lumbar region is much larger, relatively and absolutely, than the cervical region, as previously stated. The rate of growth of the lumbar region in area of cross-section is slower than that for the cervical or thoracic regions in the 65 mm. and 150 mm. embryos. This same relative decrease, like that for the volume, continues in this region in the child and adult.


This relative decrease in the lumbar and sacral regions is surprising, for it seems that since the corresponding parts of the body (the pelvis and lower extremities) increase in relative size during this period, we should expect a relative increase in this region of the cord. This decrease is evidently associated with the shortening of the spinal cord within the Vertebral canal which begins about the third month and results in the well known retraction of the lower end of the cord.


In comparing the rates of growth in volume and in average cross-sectional area of the spinal cord as a whole, let it be assumed that the volume and the cross-sectional area in the 1 1 mm. embryo each equals to 1. Then it is noted that in the 17 mm. specimen the volume has increased relatively twice as much as the area of cross-section. In the 31 mm. embryo the increase in length is to the increase in area as 3 is to 2. This relatively greater increase in volume, over the cross-sectional area, is also found in the 65 mm. and 150 mm. embryos, though not so marked in these. This indicates that the growth in length 1S relatively greater than in area of cross-section, as previously stated.

B. Gray Matter

1. General form

(tables 2 to 6; figs. 1 to 12)

The gray matter, which constitutes the cellular part of the spinal cord, in the older embryos studied shows an increase in cross-sectional area in the regions of the enlargement as compared with that found in the thoracic region. In the 11 mm. embryo, (table 2) no enlargement is found. The anterior horns form more than one—half the gray matter in all specimens studied (table 7). In the youngest embryo the anterior horn anlage is approximately three times as large as the posterior horn, which agrees with the statement of His ('86). Later, however, the posterior horns approach the anterior in size, the mid-fetal stage showing relations similar to the adult. The lateral horn is not

Well marked except in the older embryos (figs. 1 to 5). In all cases when present it is included in the measurements with the

anterior horn. The gray matter shows muchvariation in shape in diflerent segments.

2. Special features in the various regions

In the 11 mm. embryo (table 2 and fig. 6) there seems to be more gray matter (in cross-sectional area) in the cervical than in the thoracic region, but this is at least in part due to the obliquity of the sections. In the 17 mm. embryo (table 3) there is a slight increase in the area of cross-section in the cervical region (as compared with the thoracic) which probably corresponds to the cervical enlargement. The small increase shown by the lower thoracic and upper lumbar segments is due for the most part to the c1u'vature of the cord. The 31 mm., 65 mm., and 150 mm. embryos all seem to correspond to the general description (tables 4 to 6 and figs. 6 to 12). The 65 mm. embryo shows a larger area of cross-section in the lumbar region than in the cervical. In the others the cervical region is the largest. This is true for the cross-sectional area of the whole cord as well as for the gray matter.

3. Growth as a whole

The total volumes of gray matter, both absolute and relative, are given in table 1. The gray matter comprises about 38 per cent of the entire cord in the 11 mm. embryo. In the 17 mm. embryo it has increased in absolute volume approximately 300 per cent and now comprises about 50 per cent of the entire cord. The increase in absolute volume continues, but relatively slower, to the 65 mm. embryo, where it forms 58 per cent of the total cord. In the 150 mm. embryo (at the mid-fetal period) the relative volume shows a slight decrease (to 53 per cent), while the absolute volume continues to increase. This relative decrease continues into postnatal life, until in the child the gray matter forms only 27 per cent of the whole cord and in the adult only 20 per cent.


As previously stated, the anterior horns are much larger than the posterior in the earlier stages (figs. 1 to 5). The anterior horns can be distinguished in the 11 mm. embryo, although they are far from the characteristic shape assumed later. His (’86) recognized the anlages of the posterior and anterior horns early in the second month, but states that they do not assume their definite form until later, being very broad at three months. Minot (’92) found them fused at about five months. Streeter (’11) and Bryce (’08), however, state that in the 15 mm. embryo (fifth week) the rudiments of the anterior horns can be seen.

4. Growth of the various regions

(figs. 6 to 12; tables 1 and 7' to 12)

The cervical region of the cord contains relatively more gray matter by Volume than does the cord as a whole. In the 31 mm. embryo the gray matter is 57 per cent of the cervical region, while it is slightly less in the entire cord (55 per cent). This holds true in all the embryos studied, and is seen, by the data on the child and adult, to continue into postnatal life. The gray matter of the cervical region reaches the maximum relative size in the 31 mm. embryo, while in the entire "cord the mandmum percentage of gray matter is in the 65 mm. specimen. The gray matter in the thoracic region has practically theesame rate of growth as the gray matter in the cord as a whole up through the stages examined. The gray matter in the lower regions grows faster than the gray matter in the entire cord up to the 17 mm. embryo, but it grows relatively slower during the rest of the first half of prenatal life.

C. White Matter

1. Form

(figs. 1 to 5)

The various columns are indefinitely formed in the 11 mm. embryo and later gradually assume their typical shapes and relations to the gray matter. Even in the mid-fetal stage (150 mm.) the white matter still forms only a comparatively thin layer surrounding the gray matter.

2. Growth as a whole

(table 1)

The White matter shows a steady increase in the total amount both absolutely and relatively from the youngest embryo examined to the adult, as shown in table 1. In the 11 mm. specimen the white matter forms 13 per cent of the entire cord while in the 150 mm. fetus (mid-fetal period) it constitutes 46 per cent of the whole cord. In the child of two years it forms 73 per cent and in the adult 80 per cent. This is considerably different from the gray matter which, as we have seen, increases relatively up to the 65 mm. embryo but thereafter decreases relatively into the postnatal life.


The rate of growth for the various columns is somewhat irregular. This may be due to the formation of the difierent nerve tracts at different periods. Judging from the average crosssectional areas in table 8, the lateral column in the earlier stages forms more than half of the white matter of the entire cord. Later it decreases in relative size, but is always the largest column, which holds true even in the adult cord. In general the anterior and posterior columns appear relatively small at first, but in crease later, approaching the adult proportions in the later fetal days.

3. Growth in the difierent regions

(figs. 1 to 12 and tables 8 to 12)

The white matter in the cervical region of the 11 mm. and 17 mm. embryos, is relatively larger than in the cord as a whole. In the 31 mm. embryo it is about equal and in the 65 mm. and 150 mm. specimens it is less. Over 50 per cent of the total white matter of the 11 mm. embryo is in the cervical region. In the older embryos (from 3.1 mm.) a greater amount of white matter is found in the thoracic region than in any other. The length of the thoracic region accounts for the larger volume, since the area of cross-section in this region is smaller than in either the cervical or lumbar region. In each of the various regions there is a relative increase of white matter present from the youngest embryo to the adult, as found in the entire cord.

D. Ependyma with the Central Canal

1. Form

(figs. 1 to 12)

The ependyma and central canal are measured together in this study. They undergo some very marked changes during prenatal life. Only the volume and the area in cross-section are considered here. At the cephalic end where it is continuous with the fourth ventricle the canal is usually slightly enlarged. A corresponding enlargement, though somewhat more marked, is found at the caudal end of the conus medullaris where it forms the sinus rhomboidalis (which is so well marked in birds). After the 17 mm. stage the canal is decidedly narrower in the thoracicregion.

2. Growth

The cross-sectional areas of the ependyma and canal are shown in figures 1 to 12, and in tables 1 to 6, while the volumes are given in tables 1 and 9 to 11. The ependyma. with the canal in the 11 mm. embryo form 49 per cent of the volume of the entire cord. In the 17 mm. embryo they have decreased in relative size to 24 per cent but show an absolute increase. From this stage they show a decrease both in relative and in actual size until in the mid-fetal period (150 mm.) they form only 0.59 per cent of the whole cord. This decrease corresponds to the closure of the dorsal part of the central canal as described by His (’86). The ependyma and canal are too small to be shown in the curves after the 65 mm. stage. It appears that the ependyma and canal reach their maximum (absolute as well as relative) size during the second month, decreasing steadily thereafter. This agrees with Streeter (’l1) who finds them relatively and absolutely largest in the 15 mm. embryo. Minot (’92), however, says the canal remains stationary from the third to fifth months of prenatal life.


It seems that from the 17 mm. to the 65 mm. stage the gray and white matter both grow chiefly at the expense of the canal and ependyma; thereafter the white matter continues to increase, while the gray matter decreases in relative volume (percentage of the entire cord).

Summary

Some of the more important observations and conclusions concerning the growth of the spinal cord, may be summarized as follows:

  1. In the 11 mm. embryo indications of the cervical enlargement appear. In the 31 mm. embryo the lumbar enlargement is first definitely shown, though it may also be present at 17 mm. The 11 mm. cord in general tapers from the cervical end to the caudal extremity. In the 65 mm. and the 150 mm. stages the cervical and lumbar enlargements appear very prominent.
  2. The percentage which the spinal cord forms of the entire body declines rapidly during the second and third months of prenatal life and later more slowly, as shown by Jackson. The actual rate of absolute growth of the cord is much more rapid during the early prenatal months than during the later periods.
  3. The various regions of the cord form different percentages of the whole cord at difierent ages. The cervical region forms approximately 37 per cent of the whole cord in the 11 mm. embryo and decreases to 28 per cent in the mid-‘fetal stage(150 mm.). In the child and adult it forms .36 per cent and 31 per cent of the whole, respectively. In the thoracic region there is a gradual increase from 32 per cent in the 11 mm. embryo to 41 per cent in the (150 mm.) mid-fetal stage, to 45 per cent in the child, and 50 per cent in the adult. The lumbo—sacral region of the cord increases relatively from 31 per cent in the 11 mm. embryo to a. maximum of 38 per cent at 31 mm. This is followed by a gradual decrease to 31 per cent in the mid-fetal stage and to 18 per cent in both ‘child and adult. This decrease in relative size which occurs from the second month of prenatal life and extends into the postnatal period, is associated with the shortening of the cord in the vertebral canal. It is very remarkable when compared with the relative increase at the same time in the corresponding portions of the body (pelvis and lower extremities). This decrease is most marked in the sacral region of the cord. The thoracic region appears to grow at the expense of the cervical region up to about the second month of prenatal life, and thereafter at the expense of the lumbo—sacral region, continuing up to the adult cord.
  4. The gray matter constitutes about 38 per cent of the whole cord in the 11 mm. embryo increasing relatively to about 58 per cent in the 65 mm. specimen. Thereafter it decreases until in the child it forms 27 per cent and in the adult less than 20 per cent of the whole cord. The relative amount of gray matter in the cervical region from the earliest stages, and in the lumbo-sacral region from the 31 mm. stage, is slightly greater than that in the thoracic region. The anterior horn is about three times as large as the posterior horn in the youngest embryo (11 mm.). This difference in size becomes less in the later stages where the ratio approaches that found in the adult cord.
  5. The white matter has a rate of growth different from that of the gray matter. It increases steadily from 13 per cent in the 11 mm. stage to 46 per cent of the whole cord in the midfetal period (150 mm.). In the child it forms 73 per cent and in the adult 80 per cent, showing that the steady increase continues into postnatal life. In the white matter, as also in the gray matter, the relative increase in the different regions is about the same as the increase in the cord as a whole. The different columns of white matter present irregularities in growth which may be due to the successive formation of various tracts at different ages. The lateral column appears always the largest, however, especially in the earlier stages.
  6. The ependyma with the canal show some interesting growth relations. In the 11 mm. embryo they form nearly 50 per cent of the entire cord. This is followed by a rapid relative decrease until by middle of the fetal period (150 mm.) they form only 0.59 per cent of the whole. This marked relative decrease is accompanied by a decrease in the absolute size from the 17 mm. stage onward. With the exception of a slight dilation at the extremities, the canal is fairly uniform in caliber in the 11 mm. and 17 mm. stages, but from the 31 mm. stage onward it is more constricted in the thoracic region. The white and gray matter both grow at the expense of the ependyma and canal until about the third month, when the gray matter begins to decrease in relative amount while the white matter continues to increase.

Bibliography

BoNNo'r, E., AND Smnvrms, R. 1906 On the structure of a human embryo eleven millimeters in length. Anat. Anz., Bd. 39.

BRYCE, T. H. 1908 Embryology, Quain’s Anatomy, vol. I, 11th Ed. New York.

DONALDSON, H. H., AND DAVIS, D. J. 1903 A description of charts showing the areas of cross—section of the human spinal cord at the level of each spinal nerve. Jour. Comp. Neur., vol. 13.

HIS, W. 1886 Zur Geschichte des Menschlichen Riickenmarks und der Nervenwurzeln. Abh., K. Sachs. Ges. d. Wiss., Bd. 13.

JACKSON‘, C. M. 1909 a On the developmental topography of the thoracic and abdominal viscera. Anat. Rec., vol. 3. 1909b On the prenatal growth of the human body and the relative growth of the various organs and parts. Am. Jour. Anat., vol. 9.

MINOT, C. S. 1892 Human embryology. New York.

STILLING, B. 1859 Neue Untersuchungen iiber den Bau des Riickenmarkes. Casel.

STREETER, G. L. 1911 In Keibel and Mal1’s Handbuoh der Entwicklungschichte des Menschen., Bd. 2. Leipzig.

VIEBORDT, H. 1906 Anatomische, Physiologische, und Physikalische Daten und Tabellen. 3 Aufl. Jena.

Tables

Table 1

Table 1
Showing total volumes of spinal cords of various ages; the absolute and relative amounts of gray matter, of white matter, of ependyma with the canal, and of the different regions of the cord
Embryo No 60 58 57 55 54 Child Adult
Length in mm 11 17 31 65 150
Age in days (estimated) 33 41 56 81 140 2 years

Table 2

Table 2
Areas of cross-sections of the spinal cord in an 11 mm human embryo, showing the absolute and relative amounts of gray matter, of white matter, and of ependyma with canal
Segment Area of cross-section Area of gray matter Area of white matter Area of ependyma and canal % of grey matter % of white matter % of ependyma and canal
Cervical I
Cervical II
Cervical III
Cervical IV
Cervical V
Cervical VI
Cervical VII
Cervical VIII
Thoracic I
Thoracic II
Thoracic III
Thoracic IV
Thoracic V
Thoracic VI
Thoracic VII
Thoracic VIII
Thoracic IX
Thoracic X
Thoracic XI
Thoracic XII

Table 3

Table 3
Areas of cross-sections of the spinal cord in an 17 mm human embryo, showing the absolute and relative amounts of gray matter, of white matter, and of ependyma with canal
Segment Area of cross-section Area of gray matter Area of white matter Area of ependyma and canal % of grey matter % of white matter % of ependyma and canal
Cervical I
Cervical II
Cervical III
Cervical IV
Cervical V
Cervical VI
Cervical VII
Cervical VIII
Thoracic I
Thoracic II
Thoracic III
Thoracic IV
Thoracic V
Thoracic VI
Thoracic VII
Thoracic VIII
Thoracic IX
Thoracic X
Thoracic XI
Thoracic XII

Table 4

Table 4
Areas of cross-sections of the spinal cord in an 31 mm human embryo, showing the absolute and relative amounts of gray matter, of white matter, and of ependyma with canal
Segment Area of cross-section Area of gray matter Area of white matter Area of ependyma and canal % of grey matter % of white matter % of ependyma and canal
Cervical I
Cervical II
Cervical III
Cervical IV
Cervical V
Cervical VI
Cervical VII
Cervical VIII
Thoracic I
Thoracic II
Thoracic III
Thoracic IV
Thoracic V
Thoracic VI
Thoracic VII
Thoracic VIII
Thoracic IX
Thoracic X
Thoracic XI
Thoracic XII

Table 5

Table 2
Areas of cross-sections of the spinal cord in an 65 mm human embryo, showing the absolute and relative amounts of gray matter, of white matter, and of ependyma with canal
Segment Area of cross-section Area of gray matter Area of white matter Area of ependyma and canal % of grey matter % of white matter % of ependyma and canal
Cervical I
Cervical II
Cervical III
Cervical IV
Cervical V
Cervical VI
Cervical VII
Cervical VIII
Thoracic I
Thoracic II
Thoracic III
Thoracic IV
Thoracic V
Thoracic VI
Thoracic VII
Thoracic VIII
Thoracic IX
Thoracic X
Thoracic XI
Thoracic XII

Areas of cross—sections of the spinal cord in a 65 mm. human embryo, showing absolute and relative amounts of gray matter, of white matter, and of ependyma with canal



smcumrrr or cnoss- or GRAY Epmxnnu sue-non MATTER Am, cm“

Cervical I (2. 07) Cervical II (1 _ 95) Cervical III 1_ 30 Cervical IV 1 _ 77 Cervical V L90 Cervical VI 1 _ 82 Cervical VII 1 _ 51 Cervical VIII 2_o4 Thoracic I 2. 15 Thoracic II 2_ 35 Thoracic III 1. 92 Thoracic IV 2.03 Thoracic V 2.03 Thoracic VI 2_45 Thoracic VII 2_31 Thoracic VIII 2_ 73 Thoracic IX 2_ 55 Thoracic X 2_ 32 Thoracic XI 2_ 25 Thoracic XII 2_12 Lumbar 1 1.98 Lumbar II 2_ 20 Lumbar III 1 . 66 Lumbar IV 1. 72 Lumbar V 1 _ 83 Sacral I 232 Sacral II 163 Sacral III 2_ 26 Sacral IV 3_ 10 Sacral V 3.57 Coccygeal . . . . . . 5_ 55 Conusmed..... L92 Filum term..... 1419

Table 6

Table 6
Areas of cross-sections of the spinal cord in an 150 mm human embryo, showing the absolute and relative amounts of gray matter, of white matter, and of ependyma with canal
Segment Area of cross-section Area of gray matter Area of white matter Area of ependyma and canal % of grey matter % of white matter % of ependyma and canal
Cervical I
Cervical II
Cervical III
Cervical IV
Cervical V
Cervical VI
Cervical VII
Cervical VIII
Thoracic I
Thoracic II
Thoracic III
Thoracic IV
Thoracic V
Thoracic VI
Thoracic VII
Thoracic VIII
Thoracic IX
Thoracic X
Thoracic XI
Thoracic XII

Areas of cross-sections of the spinal cord in a 150 mm. human embryo, showing abso lute and relative amounts of gray matter, of white matter, and of ependyma with canal


AREA AREA % or or caosa- or can smcrrox Murrmn


Cervical I (0.72) Cervical II (0.64) Cervical III (0.65) Cervical IV 0. 60 Cervical V 0. 64 Cervical VI 0. 62 Cervical VII 0. 67 Cervical VIII 0. 76 Thoracic I 0. 66 Tlioracic II 0.71 Thoracic III 0. 67 Thoracic IV 0.48 Thoracic V 0.50 Thoracic VI 0.48 Thoracic VII 0. 65 Thoracic VIII 0 . 66 Thoracic IX 0. 60 Thoracic X 0.57 Thoracic XI 0. 64 Thoracic XII 0. 54 Lumbar I 0.47 Lumbar II 0.38 Lumbar III 0.4) Lumbar IV 0. 33 Lumbar V 0.33 Sacral 1 0.42 Sacral II 0.40 Sacral III 0.38 Sacral IV 0. 56 Sacral V 0.90 Coecygeal . . . . . . 1 .22

Conusmed..... Filumtel-m.....

Table 7

Table 7
Showing the average cross-sectional area of gray matter in the various regions, and the relative amounts of the anterior and posterior horns
Region Embryo Child Adult
11 mm 17 mm 31 mm 65 mm 150 mm
Cervical V, VI, VII, VIII Area of gray matter (sq. mm)

(%) Ant. horn

(%) Post. horn

Thoracic Area of gray matter (sq. mm)

(%) Ant. horn

(%) Post. horn

Lumbar Area of gray matter (sq. mm)

(%) Ant. horn

(%) Post. horn

TABLE 7

Showing the average cross—sectional area of gray matter in the various regions, and the relative amounts of the anterior and posterior horns


mmanyo cmnn ADULT xmoron 11 mm. 17 mm. 31 mm. 65 mm. 150mm. (Smilax)

Area of gray matter Cervical V. VI, (sq. 0.201 0.621 0.893 0.924 3.867 15.91 17.89 'VI_I, VIII.. . .. (%) Ant. horn . 74.63 69.40 58.45 62.45 54.69 58.80 [(%) Post. horn ....... .. 25.37 30.60 41.55 37.55 45.31 41.20

Areaofgray matter Thomdc ' (sq. mm. . . . . . . . . . . . . 0.142 0.454 0.460 0.625 1.382 6.45 5.36 ' ' ' ' ' ' ' ' ' " (%) Ant. horn... . 72.03 58.69 64.48 53.62 49.16 (%) Post. horn....... . . . 20.42 27.97 41.31 35.52 46.38 50.84

Area of gray matter L“mbN_ (sq. mm.) . . . . . . . . . . . . 0.515 0.790 1.326 3.165 14.55 14.41 ' ' ' ' ' " (%) Ant. horn ......... .. 73.59 56.58 57.16 55.04 52.80 (%) Post. horn ........ . . 26.41 43.42 42.84 44.96 47.20

Table 8

Table 8
Showing the average cross-sectional area of white matter in the various regions, and the relative amounts of the anterior, lateral, and posterior columns
Region Embryo Child Adult
11 mm 17 mm 31 mm 65 mm 150 mm
Cervical V, VI, VII, VIII Area of white matter (sq. mm)

(%) Post. column

(%) Lat. column

(%) Ant. column

Thoracic Area of white matter (sq. mm)

(%) Post. column

(%) Lat. column

(%) Ant. column

Lumbar Area of white matter (sq. mm)

(%) Post. column

(%) Lat. column

(%) Ant. column


TABLE 8

Showing the average cross-sectional area of white matter in the various regions, and the relative amounts of the anterior, lateral, and posterior columns

Emmro crnnn 8111711112231017 ‘—'“—‘j‘——"‘—**—“‘ 11m1n.l17mn1. 31mm. 65mm. 150mm. (stilling)


Area of white matter

(sq. mm.) .......... .. 0.082 0.357 0.571 0.701 3.019 42.24 37.64 Cervical V, VI, (%)I’osi:.column. 36.59 20.45 35.20 28.10 25.55 33.00 'VII,VIII ..... .. (%)Lat.column.. .}63fl {59.38 51.14 48.08 41.75 36.40 (%) Ant. column ..... .. ' 20.17 13.66 23.82 32.70 30.60

Area of white matte (sq. mm.) .......... .. 0.05 0.245 0.336 0.453 1.387 23.47 34.22 Thoracic ........ .. (%) Post. column. 38.00 20.41 35.71 26.27 32.30 27.60 (%)La.t.oolumn.. .}620o {(10.00 51.49 46.14 45.93 54.05 (%) ant. column ...... .. ' 10.59 12.80 27.59 21.77 18.35

Area of white matter


(sq. mm.) ........... .. 0.27 0.444 0.910 2.321 21.88 20.80 Lumbar . . . . . . . . . . (%) Post. column. . . . 20.43 26.80 31.65 34.38 30.20 (%) lat. column ...... .. 56. 99 53.40 47.47 40.84 39.30 L(%)A11t,oolumn ..... .. 22.58 I 19.80 | 20.88 24.78 31.00


Table 9

Template:Miller1913 table9

TABLE 9

Absolute and relative volumes of white matter, of gray matter, and‘ of ependyma with the canal in various regions of the cord in the 11 mm. and 17 mm. embryos

11 MM. 11114131110 17 MM. EMBBYO nrcmox ' ’

White matter . . . . . . . . .

Cervit-aL....... Gray 1natter........ . Canaland ependyma

White matter . . . . . . . . .

Thoracic ...... . . Gray matter ........ . .' Canal and ependyma

{White matter ....... . .

Lumbo-Sacmiu Gray1ns.tter..........

[Canal and ependyma

Table 10

Template:Miller1913 table10

TABLE 10 Absolute and relative volumes of white matter, of gray matter, and of ependyma with the canal in various regions of the cord in the 31 mm. and 6'6 mm. embryos

I 31 Ill. mmnro 05 Ian. minute

I _ I0 0 “ ‘ " v......... | gggn mg v..x...... ,z;,gg_ 233, O0. 06. : White matter . . . . . . . . . 0.00187 32.04 27.26 0.01625 38.80 26.07 Cfl'VI¢l1 ...... . . Gray matter ........ .. 0.00320 50.80 28.08 0.02480 50.22 28.40 Canal and ependymn 0.00000 10.47

I i 22.39 I 0.00083 1.08 25.70


White matter......... 0.00270 37.35 40.23 0.02044 44.00 43.88

Thoracic ...... .. -Gray . . . 0.00427 55.07 35.00 0.03181 54.02 30.55

Canal and ependyma 0.00050 7.58 20.80 0.00004 1.08 10.81

White matter ....... . . 0.00157 30.78 22.80 0.01182 - 37.52 10.01

Lumbar ...... . . Gray matter ........ .. 0.00284 55.04 24.40 0.01800 59.05 21.37

' Canal and opendyma 0.00000 13.58 25.75 0.00108 3.43 33.44

. White matter ....... . . 0.00000 22.52 0.02 0.00575 31.49 9.54

Sacral . . . . . . . . . . Gray matter ........ . . 0.00144 40.15 12.40 0.01183 04.79 13.59 Canal aad ependyma 0.00083 28.33 30.07

0.00068 3.73 21.05

Table 11

Template:Miller1913 table11

TABLE 11

Absolute and relative volumes of white matter, of gray matter, and of ependyma with the canal in various regions of the cord in the 160 mm. embryo.

nloron vomun Rfifgu Tag 66. White matter . . . . . . . . . . . . . . . . . . . . . . .. 0.04848 44.16 26.47

Cervical... Gray matter . . . . . . . . . . . . . . . . . . . . . . . . . 0.06059 55.19 28.65

Canal and ependyma . . . . . . . . . . . . . . . . . 0.00071 0.65 30.60

White matter . . . . . . . . . . . . . . . . . . . . . . .. 0.08087 49.31 44.16

Thoracic.. {Gray matter . . . . . . . . . . . . . . . . . . . . . . . .. 0.08213 50.09 38.82

Canal and ependyma . . . . . . . . . . . . . . . . . 0.00100 0.60 43.10

White matter . . . . . . . . . . . . . . . . . . . . . . . .. 0.03336 43.25 18.22

Lumbar. . . {Gray matter.- . . . . . . . . . . . . . . . . . . . . . . . . 0.04345 56.33 20.57

Canal andependyma . . . . . . . . . . . . . . . .. 0.00032 0.42 13.80

White matter . . . . . . . . . . . . . . . . . . . . . . .. 0.020% 44.41 11.15

Sacral. Gray matter . . . . . . . . . . . . . . . . . . . . 0.02528 54.96 11.96

Canal and ependyma . . . . . . . . . . . . . . . 0.00029 0.63 12.50

Table 12

Template:Miller1913 table12

TABLE 12

Relative volumes of white matter and of gray matter in the various regions of the spinal cord in a child of two years (Stilling) and in a composite adult (Donaldson and Davis).

CHILD ADULT

%°“°=-I

BEGION



Cervical {White matter . . . . . . . . . . . . . . . 31.27

Gray matter. . . ._ . . . . . . . ..... 31.4] Thoracic {White matter. . . . . . . . . . . . . . . 53.20

' ' Gray matter . . . . . . . . . . . . . . . . 36,89

Lumbar {White matter . . . . . . . . . . . . . . . ' 12.99

‘ " Gray matter . . . . . . . . . . . . . . . . 22.14

sacral {White matter . . . . . . . . . . . . . . . 2.54

" ' " Gray matter . . . . . . . . . . . . . . . .

Explanation of Figures

Figures 1 to 5 represent outline drawings of actual cross-sections of different regions in the various spinal cords studied. X 12. Where the sections drawn did not show any nerve roots, the lines of separation for the various columns of white matter were approximated. 6', central canal; E, ependyma; P, posterior horns of gray matter; A, anterior horns of gray matter; I, lateral columns of white matter; 12, posterior columns of white matter; a, anterior columns of white matter

Fig. 1 a 5th cervical segment, 11 mm. embryo.

Fig. 1 b 5th thoracic segment, 11 mm. embryo.

Fig. 2 a 5th cervical segment, 17 mm. embryo.

Fig. 2 b 5th thoracic segment, 17 mm. embryo.

Fig. 3 a 5th cervical segment, 31 mm. embryo.

Fig. 3 b 5th thoracic segment, 31 mm. embryo.

Fig. 3 c 4th lumbar segment, 31 mm. embryo.

Fig. 4 a 5th cervical segment, 65 mm. embryo.

Fig. 4 b 6th thoracic segment, 65 mm. embryo.

Fig. 4 c 4th lumbar segment, 65 mm. embryo.

Fig. 5 a 5th cervical segment, 150 mm. embryo.

Fig. 5 b 6th thoracic segment, 150 mm. embryo.

Fig. 5 c 4th lumbar segment, 150 mm. embryo. 65

Figures 6 to 12 represent by curves the cross-sectional areas in each segment of several embryonic and adult human spinal cords, as well as the corresponding areas of gray and white matter (also the ependyma with the canal in figures 6 to 9). The curves are so plotted that the areas enclosed between the base-lines and curves represent the total volumes of the cords and of their component parts, respectively. The figures are so drawn that the areas representing the total volumes of the cords are approidmately the same. The lengths of the segments are represented on the abscissa and so calculated that the total lengths of the various cords are represented by the same length of abscissa.

In any given figure, the changes in the height of the curves therefore represent changes in the caliber of the cord as a whole (or in the relative amounts of its component parts) at difierent levels. A comparison of the different figures shows for the various stages the changes in the form of the cord as a whole, and in the relative amounts of the component parts. The following points must be held in mind to avoid error in comparing the various curves:

1. Curves of figures 6, 7 and 8 are incomplete at the lower end.

2. Curves of figures 9 and 10 are estimated at the upper end (dotted lines) as explained in the text.

3. The apparent increase at the upper end (all of the cervical region) of figure 6 is mostly due to the obliquity of the sections corresponding to the curvature of the spinal card. This also applies to the lower.six thoracic segments of figure 6, to the lumbar segments of figure 7, and to the upper four cervical, to some extent, in figure 8. In figure 9, all the cervical segments are thus slightly enlarged, although not enough to require dotted lines.


Fig. 10 Spinal cord of human embryo of 150 mm.


Fig. 11 Spinal cord of a two-year—old child; data taktm from Stilling’s observations.


Fig. 12 Spinal cord of a. composite adult; data from Donaldson and Davis, which were calculated from the data. of four adult cords given by Stilling.



Cite this page: Hill, M.A. (2019, August 20) Embryology Paper - Prenatal growth of the human spinal cord. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_Prenatal_growth_of_the_human_spinal_cord

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