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Mall FP. VIII. Determination of the age of human embryos and fetuses in Keibel F. and Mall FP. Manual of Human Embryology I. (1910) J. B. Lippincott Company, Philadelphia.

VIII. Determination of the Age of Human Embryos and Fetuses

Franklin Mall (1862-1917)

By Franklin P. Mall of Bailtmore.

It would be relatively easy to determine the age of human embryos were it possible to fix with certainty the time of conception, that is, the time at which the spermatozoon enters the ovum. However, this question, which is directly associated with that of the duration of pregnancy, and must be discussed with it, has been a most important one in anatomy for ages, and it appears to be gradually approaching a satisfactory solution.

In ancient times it was generally believed that the duration of pregnancy in man, unlike that in lower animals, was of very uncertain length ; and it was not until the seventeenth century that it was more accurately fixed, by Fidele of Palermo, at forty weeks, counting from the last menstrual period. In the next century Haller found that if pregnancy is reckoned from the time of a fruitful copulation it is usually thirty-nine weeks, and rarely forty weeks in duration. In general these results are fully confirmed by the thousands of careful data collected during the nineteenth century.

The difficulties encountered in determining the age of an embryo are due to the impossibility of determining the exact time of fertilization, for this does not necessarily follow immediately after copulation, and it is related only in a loose way with menstruation, the error in calculation in the second case often being a full month ; but to the present time it has been most convenient, and probably most nearly correct, to rate the age of an embryo and the duration of pregnancy from the last menstrual period. However, from thousands of records it is found that the mean duration of pregnancy varies in first and second pregnancies, is more protracted in healthy women, in married women, in winter, and in the upper classes. As in lower animals, it varies very much in individual cases independently of any assignable cause. In general, it is longer when the new-bom infants are over 50 cm. long, the mean difference being, according to Issmer, fifteen days between those that are 48 cm. and those that are 53 cm. long. Furthermore, it is well known that other mammalian embryos of the same age vary much in size, and, although we have a variety of data which bear upon the time of conception and the age of young human embryos, none are of more value, as Von Baer has pointed out, than those obtained from comparative embryology. The first step toward the solution of the problem was made by Von Baer when he discovered the human ovum. Next it was proved by Bischoff that ova are usually liberated periodically during the menstrual period, independently of copulation, and that the Graafian follicles of the ovary which contained these are converted into corpora lutea. Thus the first step was taken, for it had been shown that a recent ovulation is marked by a fresh corpus luteum and that in turn this usually takes place during the menstrual period.

The excellent work of Bischoff on fertilization in the rabbit and dog demonstrated that soon after copulation the spermatozoa pass through the uterus into the tube, where the ovum is usually met. When copulation takes place during the period of rut the ovum is usually fertilized within twenty-four hours, and in case the ovum is not fertilized upon the surface of the ovary or in the upper end of the tube it soon degenerates. However, this second point is not well established for mammals, but it is known that unfertilized hen's eggs can not be fertilized in the lower part of the oviduct. Since segmentation takes place in the mammalian ovum while it is in the uterine tube it is highly improbable that a human ovum could be fertilized after it has reached the uterus, but instead is probably always fertilized upon the surface of the ovary or in the upper part of the tube, as the frequency of tubal pregnancies indicates.

In 1868 Beichert obtained a very small human ovum measuring 5.5 by 3.3 mm from a woman who commited suicide exactly two weeks after her menstrual period failed to appear. This ovum was studied with great care and described at great length by Eeichert, and has become the classic specimen upon which to reckon the age of young human ova as well as to fix the time of fertilization. In one ovary there was found a well-developed corpus luteum with but very little blood in its centre. Eeichert then studied the condition of the ovaries during menstruation and found that in nineteen specimens out of twenty-three the Graafian follicles had ruptured in the beginning of the period, while in four they were still unruptured. From these observations he concluded that, as a rule, ovulation takes place just before menstruation and that in case the ovum is fertilized menstruation is missed. This view changed the entire aspect of the question at once. Formerly it was believed that the ovum came down the tube slowly and was fertilized some days or weeks later, and now Eeichert was led to believe that ovulation and fertilization took place but a few days before menstruation and that the presence of a microscopic fertilized ovum in the upper end of the tube arrested entirely the menstrual hemorrhage which was about to appear. With great force he discussed the whole question and decided that his specimen must be two weeks and not six weeks old. Already Von Baer had noted that the human ovum was precocious in its early development, but Beichert's conclusion made it much more so. However, it was easier to believe that Reichert's ovum was two weeks than six weeks old and there seemed to be no other possibility. The theory of Keichert regarding the time of conception was accepted by His as the most probable, and accordingly he gave the probable age of embryos up to 35 mm. long. Due to his great influence the Eeichert theory has been generally accepted and the most remarkable distortions have been made to fit individual specimens into it. The best known case is the Peters ovum, a specimen 1.6 X 0.9 mm. which was obtained thirty days after the last period, and Peters estimates its age to be three or four days. according to Weysse a pig's ovum of the same size is from nine to eleven days old, and according to Bischoff and Bonnet a dog's ovum 2 mm. in diameter is from twelve to fourteen days old. Unfortunately Peters does not describe the condition of the corpus luleum in this specimen, at present the only reliable index by which we can hope to determine the age of young ova. It is imperative that we standardize the corpus luteum of the first weeks of pregnancy and that in all cases when embryos are obtained at autopsy the ovaries should be carefully described and sections of the corpus luteum should be made and pictured.

The ovum of Merttens, 3x2 mm, was obtained from a uterine scraping twenty-one days after the last period. Here there was no lapsed period, and twenty-one or fewer days does not seem to me to be an unreasonable age for a human ovum 3 mm. in diameter. That the Peters ovum was older than four days is indicated by the morning sickness that preceded the lapsed period, and, if I am not mistaken, morning sickness is sometimes the first sign of pregnancy.

Among the records of embryos under 5 mm long I have been able to find thirty-six with menstrual history given (Fig 147). according to the Eeichert-His theory about twenty-five days would have to be subtracted from the ages of twenty-seven of them to make them correspond with the remaining nine. In other words. His would rate nine of them from the last period and twentyseven from the first lapsed period. We are evidently dealing with two groups of young embryos which correspond with ovulations of two menstrual periods, but which two is still uncertain. Must we add twenty-eight days to each of the group of nine or subtract twenty-eight days from the group of twenty-seven?

The investigations of Bischoff, Dalton, Williams, Eeichert, Arnold, Leopold, Leopold and Mironoff, and Leopold and Ravano have shown conclusively that ovulation and menstruation are usually synchronous, but menstruation often occurs without ovulation and sometimes ovulation takes place in the intermenstrual period. In Leopold and Mironoff's fortytwo cases ovulation occurs thirty times with menstruation, once without, and ten times there is menstruation without ovulation. The ninety-five selected cases of Leopold and Ravano show that ovulation and menstruation coincide in fifty-nine and are independent of each other in the remaining thirty-six cases. In other words, the connection between ovulation and menstruation is very loose and the two coincide in only two-thirds of the cases. Furthermore, ovulation occurs frequently during pregnancy. [Ravano.]

The data of the other investigators give a similar distribution of ovulations, and there is no marked evidence that ovulation precedes menstruation, as is required if Reichert's theory is true. It is to be hoped that this subject will be carefully studied in some large clinic where many normal ovaries are examined in abdominal operations. Then the age of corpora lutea could be standardized and subsequently applied to autopsy and other cases in which young ova are found in the uterus. In the recent work of Leopold and Ravano only the estimated age of the corpus luteum is used to determine the time of ovulation in relation to menstruation. At the present time their determination of the age of the corpus luteum is the best which we possess, but I believe that it is possible to standardize better the corpus luteum of the first week, that is, those which are formed during menstruation. This must be studied first, then that of the second week, and so on. Through this method we can determine with much greater precision the probable age of a corpus luteum.

At any rate, the separation of young human embryos of the same size into two groups to correspond with two previous menstrual periods indicates that pregnancy usually takes place in the neighborhood of menstrual periods, and facts regarding the duration of pregnancy bear this out. Leuckart tabulated 110 cases of births during the first ten months of married life and found that the maximum number were on the two hundred and seventy-fifth day, after which they fell off and increased again to a second maximum on the two hundred and ninetv-third day. He believes that in those cases which came in the first maximum the ovum was obtained from an ovulation which preceded marriage and those that fell in the second maximum belonged to the first menstruation after marriage. He was able to collect eight cases in which the menstrual history was given. In four of them, in which marriage occurred during the third and fourth week after the beginning of menstruation, the women menstruated once after marriage. In the remaining four, in which the marriage followed immediately upon the cessation of menstruation, three did not menstruate again and one menstruated but once before pregnancy. In the second case, where newly-married women do not menstruate at all, we must assimae that the ovxilation of the last period gave rise to the pregnancy; that ovulation delivered the oviun into the upper end of the tube and soon became fertilized. In the first case the spermatozoa reach the ovary and there await the ovum from the ovulation which takes place with the first menstruation after marriage. It follows from the above that a fertilization immediately before menstruation does not cause the period to lapse, which contradicts the main proposition in the Reichert-His theory. In fact women quite frequently menstruate more than once after the beginning of pregnancy, and at present there are no data to show that a woman who has not copulated since the last menstruation cannot be pregnant. Some additional light is thrown upon the question of the time of conception by a study of the duration of pregnancy as estimated from the last menstrual period as well as from the time of copulation. according to the more recent statistics of Issmer the average duration of pregnancy, in 1220 cases, is 280 days when estimated from the first day of the last menstrual period, and, in '628 cases, 269 days when estimated from the fruitful copulation. In general these two figures correspond with those of Ahlfeld, Hecker, and Hasler, who also collected about 500 cases in which the time of fruitful copulation was given. So in a group of about 1200 cases the duration of pregnancy is fully ten days longer when reckoned from the last period than when from the time of copulation. It may be noted that the data regarding fruitful copulation must be taken with the greatest reserve, for many of them are from unmarried women and in but few of them does the fruitful copulation precede the menstrual period. However, it is remarkable that the results of the different observers are practically the same, each time giving a difference of a week or ten days. Ahlfeld further classified the cases, giving the time of copulation in relation to menstruation.

Married women Unmarried women
On last day of menstruation.

Percent. 35.55 25.49

First twelve days after beginning of menstruation.

Percent. 88.44 70.98

First seven days after end of menstruation.

Per cent. 88.88 70.58

Similar figures are given by Issmer.

Time of copulation.

First week of menstrual period . . Second week of menstrual period Third week of menstrual period. Fourth week of menstrual period

Average duration of pregnancy.

277 days 279 days 287 days 285 days

From these figures it is seen that most pregnancies take place during the first week after menstruation and that the duration of pregnancy is longer if copulation takes place towards the end of the intermenstrual period. And this is explained if we assume that in the first week, especially the first few days after the cessation of menstruation, the ovum is in the upper end of the tube awaiting the sperm and that conception immediately follows copulation. When the fruitful copulation takes place in the latter two weeks of the month the opposite is usually the case; the sperm wanders to the ovary and there awaits the ovum; and, therefore, on an average, pregnancy is prolonged in this group of cases, when determined from the time of copulation. This explanation fits all the facts but opposes the Eeichert-His theory.

We have finally the argument given by comparative embryology. Why should the human ovum be precocious in its early growth? We have good data upon the rabbit, dog, pig, and sheep ; and, in general, if we apply the Keichert-His theory, the growth of the human ovum is at first far more rapid than any of them, and is then overtaken by the rabbit when the embryo is 5 mm. long, by the pig at 15 mm., and by the dog at 20 mm. The duration of pregnancy in the rabbit is 30 days ; in the dog, 63 ; in the pig, 120 ; in the sheep, 154; — why should these animals grow slower at first than man? If the age of human embryos is estimated from the last menstrual period or a few days later, a curve of growth is obtained which corresponds fairly well with that of lower animals. Possibly it may be allowable to compare early human development with that of the dog. according to Marshall ovulation in the bitch occurs after bleeding from the external opening has been going on for some days, or when it is almost or quite over. It takes place quite independently of coition. Up to this time the bitch will not copulate and unless the act is repeated fertilization does not always take place. Usually the ova are fertilized in the upper end of the tube, and segmentation is practically completed before they enter the uterus.

Growth of the dog's ovum (Bischoff)
Age in days 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 16.5
Diameter of ovum in mm 0.15 0.14 0.14 0.16 0.16 0.18 0.20 0.21 0.28 0.30 1.0 2.0 3.0 4.0 5.0 5.0 6.0

In determining the age of human embryos it is probably more nearly correct to count from the end of the last period, for all evidence points to that time as the most probable at which pregnancy takes place. The group of cases from which His did not subtract twenty-eight days in forming his curve (for instance, Hensen's embryo, which is 4.5 mm. long and was aborted on the twenty-first day) are probably much older than His thought. They belong to those cases in which women menstruated once after becoming pregnant.

Having determined the time at which pregnancy probably occurs, it is necessary to fix that at which it ends. Not only is it necessary to determine the day but also the probable size of the child, for there is as much variation in the size as in its age.

Issmer gives the following figures:
Size of child
in cm
No. of cases Age in days,
from the beginning of the last menstrual period
48 203 271
49 272 278
60 252 277
51 211 282
62 123 283
63 34 286
54 18 290

The mean length of the child at birth is 49.5 cm. Hecker found it to be 51.2 cm. in 985 cases, and Ahlfeld a little over 50 cm. If a week is allowed to elapse between the beginning of menstruation and conception then the mean new-born child is 271 days old and is 50 cm. long.

Having fixed the probable relation between ovulation and menstruation it is next necessary to relate each embryo and fetus first to the first day of the last menstrual period and then correct the same to correspond with the probable time of conception. In order to do this it is necessary to establish some standard measurements of the embryo and, if possible, to determine their deviations when expressed in time.

It is known that embryos of other mammals of the same age vary considerably in size unless they are from the same litter, when they are usually very much alike. Undoubtedly there are variations in different animals, and this must be taken into account in comparing human embryos with one another. Also we must not forget that in early abortions there are many pathological specimens, and even if the embryo is normal in appearance pathological conditions are usually the cause of the abortion. This being true the menstrual periods are also far from normal, and it is not unlikely that ovulation is more irregular than normal in these cases. Thus it is often difficult to determine accurately the last period, for it may be complicated by more or less continuous hemorrhage. With all these uncertain factors before us it is certainly remarkable that the specimens can be arranged as well as they are, especially their falling into two sharply defined groups during the first two months of pregnancy.

Until quite recently no serious attempt has been made to determine the age of embryos; it was usually estimated. In order to do this with some precision Arnold measured embryos from head to breech and Toldt from the crown to the soles of the feet (His, 1904). Although this second measurement is called an uncertain one I think that my measurements show that it varies no more than Arnold's (Fig 145 and Fig 146). These two measurements I consider the best that have been proposed. The first — the crown-rump, vertex-breech, or sitting height — and the second — the vertex-heel, crown-heel, or standing height — are standard ones used by anthropologists in measuring the body after birth. In addition to these. His has introduced a measurement for very young embryos from the elevation on top of the back of the head to the breech, the Nackenlinie; but this is of little value in measuring older embryos, and easily leads to confusion. In measuring my own specimens, as well as all those I have found suitably pictured in the literature, my attention was called to the neckbreech measurement and its meaning. As it is usually taken it is of value from the time the embryo is well curled upon itself until the neck is fairly well developed, that is, from the fourth to the seventh week. During this period this measurement is the longest, or is as long as any other, that can be made upon the embryo without stretching the legs. In later stages it equals practically the length of the vertebral column.

In order to make satisfactory measurements upon the bodies of young embryos it is necessary to measure them from more fixed points than is usually done. according to the position of the head the upper end of the longest measurement of an embryo may fall over any portion of the brain, and from a study of numerous specimens I find that the middle of the mid-brain is usually just below the highest point of the head; but whenever this is not the case, as it is found to be in young embryos, I think the measurement should still be taken from a point immediately over the mid-brain, as is shown in Fig. 141, C. The other point which I suggest as a desirable one to measure from lies in the mid-dorsal region just above the first cervical nerve, as shown in Figs. 141 and 142, which have the outlines of this nerve drawn in. In Figs. 143 and 144 this point is marked by passing a straight line from the middle of the lens through the external auditory meatus to the back of the head. In both of these specimens this line passes between the atlas and the occipital bone. This gives an upper point, between the skull and the vertebral column, which is below the one from which His drew his Nackenlinie and above the depression in the neck from which a number of embryologists make their neck-breech measurements. I have found from numerous measurements of embryos, fetuses, infants, and adults that a line drawn from the middle of point between the occioipital bone and the first vertebrae the eye through the middle of the ear and extended to the back of the neck always passes just below the foramen magnum, or slightly higher. For practical purposes it cuts the skull from the body, and according to our knowledge of the position of the eye and ear this should be the case. This line, which I have termed the oculoauricular, or eye-ear line, is of fundamental importance in measuring the length of the spinal column in embryos. Anthropologists obtain the same point between the skull and vertebral column by extending the plane between the two rows of teeth to the back of the head; "while art anatomists determine it by projecting a horizontal line through the nasal spine, just below the nares, to the back of the head ; in both cases the skull is cut oflf. All three of the lines meet in the adult at the foramen magnum; but in the embryo only the eye-ear line is of practical use, for it can be determined early and with certainty. The height of the skull, which forms the submodulus in the Fritsch-Schmidt canon, can be obtained in any embryo by measuring the distance at right angles from the above-mentioned horizontal line, through the nasal spine, to the crown (Figs. 141-144, C), that is, the point immediately over the mid-brain.

Keibel Mall 141.jpg

Fig. 141. Embryo No. 163, X 10 diameters. C, crown immediately over the mid-brain; R, rump; A. point between the occipital bone and the first vertebra. e-e eye-ear line. ;

Keibel Mall 142.jpg

Fig. 142. Embryo No. 144. X 7 diameters. Letters as in Fig. 141. H, heel; h, hip-joint; K, kneejoint; X, point in leg which equals the distance from h to i2. By adding xH to CR the standing height of the embryo is obtained.

The two upper points from which to measure being fixed just above the atlas and just over the mid-brain, it is necessary to have a lower point in order to measure the length of the head and trunk. All embryologists agree that it be placed at the lowest point of the breech. The line AR approximates the length of the spinal column and the line CR equals the sitting height of the embryo. These two lines mark respectively the atlantosacral and the mesencephalosacral measurements. In Figs. 141 and 142 the point R is exactly below the sacrum, but as the embryo grows longer (Figs. 143 and 144) the ischium gradually recedes; at birth it is considerably below the level of the sacrum. For practical purposes, therefore, the line from the foramen magnum to the rump, AR, equals the length of the spinal column. In the adult the tip of the sacrum is at the level of the middle of the acetabulum, and this latter point is naturally chosen by Fritsch in the construction of his canon. On account of the high position of the ilium in both the embryo and the fetus, and on account of the close relation between the lower end of the sacrum and the rump in them, I believe it most desirable to measure to the rump and not to the acetabulum. Furthermore, it makes one of the measurements, AR, equal the length of the spinal column, and the other, CR, the sitting height of the embryo.

A comparison of these two lines upon all four figures shows that in all cases they are the longest lines that can be drawn from the mid-brain and atlas to the rump in each case. Furthermore, as the embryos increase in size the angles these form at the rump become more and more acute. In Fig. 141 the crown-rump line falls far in front of the eye ; in Fig. 142 it is just in front, and in Fig. 143 just behind the eye ; in Fig. 144 it nearly strikes the ear.

Keibel Mall 143.jpg

Fig. 143. Embryo No. 22, X 6 diameters.

The entire length of the body, the mesencephalocalcanean line, or the standing height of the embryo, is really the best single measurement of the embryo, for it is the one usually made by obstetricians as well as by anthropologists. It has been said that the standing height of embryos and fetuses is an unsatisfactory measurement on account of its xmcertainty, but my experience obtained from the measurement of many embryos, Fig 146, shows that it is no more variable, probably less so, than either the sitting height or that of the spinal column. In Fig. 141 the sitting and the standing heights still equal each other, for, as is easily seen, the leg bud cannot be stretched beyond the rump. The other figures show that by extending the legs the standing height becomes greater than the sitting. In each of the figures the hipand kneejoints and heel are indicated by letters. If a circle is described around the head of the femur, as has been done in the figures, the portion of the length of the leg to be added to the sitting height in order to obtain the standing height is easily ascertained. In Figs. 142 and 143 this amount is only a portion of the leg, while in Fig. 144 it includes most of the thigh and all of the leg. A number of fresh embryos were measured in this way, the legs were then straightened and specimens were again measured from crown to heel, and it was found that the two measurements agreed exactly. By this method, then, the standing height of an embryo can be determined without stretching a fresh specimen or injuring a valuable one after it has been hardened.

By making a large number of measurements of the human body, Pfitzner has demonstrated that the most constant ratio of any is obtained by dividing the breadth of the head by its length. The mean index for individuals of every year, from birth to old age, is 83 in males and 82 in females. I gather from the figures of embryos and fetuses published by Retzius that in all months of uterine life the index is the same as after birth, for in the individual cases given it ranges between 80 and 85. Were it possible to apply these measurements to all fetuses, I think either the length or the breadth of the head would prove the best standard, and all other measurements could be adjusted to it as the art anatomist has adjusted all proportions to the submodulus. That other measurements are required of the body of the embryo than those that are usually made, including that of the entire length of the body, is indicated by various writers, including His, who was the first to use the Nackenlinie. More recently he employed a new measurement which he calls Kopftiefe, and which he says corresponds about to the height of the head, measured from the chin to the crown. The Kopfldnge is the length of the head, a measurement which can easily be obtained if this part of the embryo is not distorted. The point between the occipital bone and atlas having been determined, as is done by the eye-ear line, a second line may be introduced connecting the spine of the nose with it. The longest line within the head of the embryo parallel with this measures the length of the head, and a line at right angles to it extending to the crown measures the height of the head. Thus it is seen that it is possible to make some of the ordinary head measurements of the adult upon the head of the embryo. It may be that the submodulus of Fritsch-Schmidt may yet prove to be the standard measurement in human embryology, comparing all of the other measurements of the body with it, as is the case in the Fritsch-Schmidt canon of the adult. However, thispossibility appears to be remote.

Keibel Mall 144.jpg

Fig. 144. Embryo No. 131, natural size. Length of "vertebral column" 68 mm., sitting height (crown-rump or vertex-breeoh length), 90 mm.; standing height (90 + 21+23), 134 mm.

Keibel Mall 145.jpg

Fig. 145. Chart giving the standing height (CH), sitting height {CR), and vertebral column (AR) measuiements of embryos less than 90 mm. long. The abscissas are CR, and the two series of ordinates are CH and AR measurements. Each dot represents two measurements of an embryo.

Keibel Mall 146.jpg

Fig. 146. Chart shown in Fig. 145 extended to include all fetuses. The lower X are all from Burtsoher's measurements.

Keibel Mall Table-embryo and fetal age.jpg

It seems to me that for the present we must continue to employ the sitting height or the crown-rump measurement as the standard* Next in importance is the standing height, and, judging by the form of a curve made by abscissas and ordinates to determine the means by the graphic method, I do not find that one is more variable than the other (Figs. 145 and 146). The sitting height is the measurement most easily, and, therefore, the one usually made upon young specimens, and the standing height upon older ones. These two measurements can be compared directly with the two standard measurements made after birth. By means of the eyeear line the point between the head and neck can be marked and from it the length of the head, and of the skull, may be obtained. That the standing height is just as good a measurement as the sitting height is further found by the experience of Pfitzner, who was at first opposed to it, but after having made many more measurements he selected it as the best standard measurement with which to compare all others. This last statement is based upon the careful measurements of 5000 cadavers.

All the measurements that I have been able to collect from the literature, by correspondence, and from my own specimens, are given in the two curves (Figs. 145 and 146). These were tabulated with the crown-rump measurements as abscissas and the standing heights as ordinates. In the embryos and smaller fetuses a second set of ordinates gives the length of the vertebral column, and it is seen that the deviations here are quite marked. The rows of dots were then divided by curves which included half of the cases, leaving one-quarter on one side and the other quarter on the other. The dots which fell between the two lines mark probable deviations and a line drawn midway between them gives the probable mean. By this method a probable mean is determined in a graphic way from a relatively small number of cases. From the two curves the means of all the measurements in any specimen may be obtained at a glance. This is necessary, for the age of embryos with the standing height given had to be compared with those in which the sitting height is given. In the embryos with a CR measurement less than 13 mm. long there is considerable deviation on account of the irregularity of these young specimens, their smallness, and the great probable error in making the CR and AR measurements. In embryos 13 mm. long the legs begin to grow and the CR and CH measurements form a very even curve, but the deviation of the AR measurement is very marked, showing that it is not altogether satisfactory.

Having remeasured in three directions after a uniform plan all the embryos I could collect it is now possible to tabulate them in relation to the menstrual history, and the curve is by no means as satisfactory as I had hoped it to be. However, it must stand for the present, and new and much better material is needed before it can be revised. Even if we should limit ourselves to specimens got from mechanical abortions, operations, and autopsies we must still reckon on 6 per cent, of abnormalities, which are present in all pregnancies. The cases given in the two curves have been shifted and tested, and again and again controlled by the curves of Hecker, Ahlfeld, Toldt, His, Issmer, and Michaelis, and it seems to me that they are the best that can be done with the data at hand. Towards the end of pregnancy I have allowed Ahlfeld 's and Issmer *s data to influence my curve a little ; for a number of the measurements of my older fetuses came from negroes, and their statements are not as reliable as they might be. At the beginning of the curve I have deviated considerably from His for reasons given above. Toldt's curve is largely an opinion, as he states in his article. The other specimens from the latter months of pregnancy (Issmer, Ahlfeld, and Michaelis) are from exact data and are very reliable. In transferring Michaelis 's means I placed it in the middle of the month and not at the end. The His curve is constructed from measurements taken from his "Normentafel" and the higher line gives his Nackenlinie. In all other cases the CH measurement is given as soon as the legs begin to develop.

The great amount of scattering of early specimens, as shown in Fig 147, is due no doubt in part to an arrest of development, on the one hand, and continued menstruation after pregnancy, on the other. In order to get any kind of agreement His, in the construction of his curve of growth, deducted about twenty-eight days from the age of many specimens in order to make them agree with the rest. However, his curve which I have introduced is an irregular one, unlike the probable curve obtained by tabulating any growing organic body.

Keibel Mall 147.jpg

Fig. 147. — Chart giving specimens with menstrual history in embryos less than 80 mm long (CH). The curves of His, Told and Michaelis are included. My curve is given with all three measurements. The embryos where the age could also be traced back to a single copulation are inserted into a second time and marked with a star (<no wiki>*</no wiki>). Thus an embryo 30 mm long (CH) was aborted fifty-six days after the fruitful copulation and seventy-five days after the beginning of the last menstrual period. The curves marked CH represent standing height, CR sitting height and AR length of vertebral column.

Keibel Mall 148.jpg

Fig. 148.

Keibel Mall Table-embryo length.jpg

  • From the literature: Re4zius, MJerkel, Burtscher, Sommerring, Ecker Kolliker, 0. Schultze, Kollmann, Heisler, Minot, His, Frederic, Fraser, Keibel,. Bade, Bonnet, Piersol, Rabl, Tandler, Merttens, Reichert, Peters, Graf Spee, Frassi, fetemod, Thomson, Hensen, Janosik, Meyer, Stubenrauch, and Wagner.

Through correspondence : From Professors Graf Spee, Laguesse, Hasse, Robinson, Edwards, Hrdlicka, Streeter, Jackson, Bruner, Lee, Meyer, Waldeyer, Brachet, Keibel, Gage, Thomson, Austrian and Mandelbaum.

(Table 4 here - see Discussion page)

There are a few cases in which the time of copnlation as well as that of menstruation is given in the history of young embryos. These I have brought together in the above table, and I have also entered them with a * in Fig 147. That is, the age of the embryo, as rated by the only copulation between the menstruation and the abortion, is also given. From this it is evident that the most probable time of conception is during the first week after the menstrual period, as advocated by Hensen and most obstetricians.

This view is supported by all the evidence, including that obtained by the study of early human embryos. Among civilized races copulation does not take place during the menstrual period, and it is believed that it is most likely to be followed by pregnancy if it occurs immediately after the period. Furthermore, competent authorities recommend that women who are anxious to become pregnant should copulate before the period is fully over. If it is true that ovulation takes place towards the end of the period the ovum is most likely to become fertilized if it is met by a host of spermatozoa in the tube. After the spermatozoa have passed through the tube the probability of fertilization is reduced. In such cases pregnancy should occur within twentyfour hours after copulation. If the sperm awaits the ovum, as is the case when the copulation takes place some time before the period, the probability of fertilization is greatly reduced, and if it occurs it is only after the lapse of a number of days. This accounts for the discrepancies given by Issmer. That conditions regarding the relation of fertilization to menstruation and to the oestrous cycle are identical is further proved by the habit of American negroes, who, I am informed by Professor Williams, prefer to copulate during the menstrual period. At this time the odors of the negress are said to excite the passion of the negro and are very attractive to him.

The following table gives the probable deviation of the length of embryos and of the menstrual age, that is, the age as computed from the first day of menstruation. I have also included in it the figures given by Michaelis. Since he gives the mean for each month I have given his data for the last day of the second week, for, as I take it, his mean measurements apply to the middle of the month. The probable age which is the basis for this table is given in the form of a curve in Fig 148. It may be noted that its form during the first month (Fig 147) is somewhat drawn out and does not correspond any too well with the curve during the remaining nine months of pregnancy. However, in embryos up to 10 mm. long the CR measurement is less than that of the spinal column, while later on it exceeds it. In fact it is the diameter of a circle in very young embryos, while later on it is half of the circumference. This Toldt attempted to correct. The His curve is very irregular in form and for this reason, if for no other, cannot be correct. It falls between Toldt 's and mine.

■ " Probable deviation " Includes Tulf of the meuuTemenl t The data of Mlchsellfl are placed In Ibe middle of the m 1 Includes 140 BperimphB. i figures In biacketa are estlmaUotia

Keibel Mall 148.jpg

Fig. 148. — Curves shown in Fig. 147 extended throughout the ten months of pregnancy. The individual cases are not given. CH, standing height; CR, sitting height; AR, length of spinal column. The curves with the exception of Toldt's and His's are constructed from actual specimens in which the menstrual history is given. Toldt's is an estimation based upon the literature. His's own estimation based upon the Reiohert-His theory.


Ahlfeld: Monatsschrift fiir Geburtskunde, vol. xxxiv, 1869.

Arnold: Inaug. Diss. Wiirzburg, 1887.

Von Baer: De Ovi Mammalium et Hominis Genesi. Epistola, Leipzig, 1827.

Entwicklungsgeschichte der Tiere, 1828.

Bischopf: Beweis der von der Begattung unabhangigen periodischen Reifung und Losung der Eier der Saugetiere und des Menschen als erste Bedingung ihrer Fortpflanzung, Giessen, 1844. Entwicklung des Hundeeies, 1845.

Bonnet: Beitrage zur Embryologie des Hundes, Anat. Hefte, vol. ix, 1897. Entwicklungsgeschichte der Haussaugetiere, 1891.

Bryce and Teacher: Contributions to the Study of the Early Development and Imbedding of the Human Ovum, Glasgow, 1908.

Bryce TH. and Teacher JH. Contributions To The Study Of The Early Development And Imbedding Of The Human Ovum 1. An Early Ovum Imbedded In The Decidua. (1908) James Maclehose and Sons. Glasgow.

Dalton JC. Prize essay on the corpus luteum of menstruation and pregnancy. (1851) Philadelphia: T.K. and P.G. Collins.

Fritsch: Die Gestalt des Menschen, 1899.

Hasler: Inaug. Diss., Ziirich, 1876.

Hecker: Klinik fiir Geburtskunde, 1861.

Hensen: Hermanns Handbuch der Physiologic, vol. vi, 1881.

His W. Anatomie Menschliche Embryonen I - Embryonen des ersten monats (Anatomy of human embryos - Embryos of the first month). (1880) Leipzig.

His: Anatomic menschlicher Embryonen, Leipzig, 1880.

Die Entwicklung des menschlichen Gehims, Leipzig, 1904.

Issmer: Arch. f. Gynakol., vol. xxxv. (For literature upon the history of the duration of pregnancy, 1889.)

Keibel F. Normal Plates of the Development of the Pig Embryo (Sus scrofa domesticus). (1897) Vol. 1 in series by Keibel F. Normal plates of the development of vertebrates (Normentafeln zur Entwicklungsgeschichte der Wirbelthiere) Fisher, Jena., Germany.

Leopold: Arch. f. Gynakol., vol. xxi, 1883.

Leopold and Mirinoff: Arch. f. Gynakol., vol. xlv, 1894.

Leopold and Ravano: Arch. f. Gynakol., vol. Ixxxiii, 1907.

Leuckart : Wagners Handworterbuch der Physiologic, vol. iv, 1853.

Loevenhardt: Arch. f. Gynakol., vol. iii, 1872.

Mall FP. A contribution to the study of the pathology of early human embryos, (1900) Johns Hopkins Hosp. Rep., 9: 1-68. Mall FP. Normal plates of the development of vertebrates. Anat. Rec, (1908). (Both papers give many of the measurements which are used in the construction of the tables and figures of Chapter VIII.) Mall FP. On measuring human embryos. Anat. Rec, (1907) 1: 129-140.

Marshall: Phil. Trans. Roy. Soc, 1905.

Merttens: Zeitschrift f. Geburtsh. und G3Tiakol., vol. xxxix, 1894.

Michaelis: Arch. f. Gynakol., vol. Ixxviii, 1906.

Minot CS. and Taylor E. Normal Plates of the Development of the Rabbit Embryo (Lepus cuniculus). Vol. 5 in series by Keibel F. Normal plates of the development of vertebrates (Normentafeln zur Entwicklungsgeschichte der Wirbelthiere) Fisher, Jena., Germany.

Peters: Einbettung des menschlichen Eies, Leipzig und Wien, 1899.

Pfitzner : Zeitschrift f . Morpholog. und Anthropolog., vols, i and v, 1899 and 1903. Ravano: Arch. f. Gynakol., vol. Ixxxiii, 1907.

Reichert : Beschreibung einer f riihzeitigen menschlichen Frucht im blasenf ormigen Bildungszustande, Abb. Kgl. Akad. Wiss., Berlin, 1873.

Retzius: Biol. Untersuch., vol. xi, 1904.

Strassmann: in Von Winkel's Handbuch d. Geburtsh., vol. i, 1903.

Toldt: Prager med. Wochenschrift, 1879.

Weysse : The Blastodermic Vesicle of Sus Scrof a, Proc. Amer. Acad, of Arts and Science, vol. xxx, 1894.

Weysse AW. On the blastodermic vesicle of sus scrofa domesticus. (1894) Proc. Amer. Acad. of Arts and Science 3: 283-321.

   Manual of Human Embryology I 1910: The Germ Cells | Fertilization | Segmentation | First Primitive Segment | Gastrulation | External Form | Placenta | Human Embryo and Fetus Age | Ovum Pathology | Integument | Skeleton and Connective Tissues | Muscular System | Coelom and Diaphragm | Figures | Manual of Human Embryology 1 | Manual of Human Embryology 2 | Franz Keibel | Franklin Mall | Embryology History

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