Paper - Contributions to the history of the structure of the human ovum and embryo before the third week after conception (1839)

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Thomson A. Contributions to the history of the structure of the human ovum and embryo before the third week after conception, with a description of some early ova: Part I. (1839) Edinb Med Surg J. 52(140):119-136. PMID 30330738

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This 1839 historic paper by Thomson is an early description of human development from fertilization.

See also by anther later Thomson author: Thomson A. The maturation of the human ovum. (1919) J Anat. 53(2-3): 172-208. PMID 17103860

Modern Notes: oocyte | morula | blastocyst

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Contributions to the History of the Structure of the Human Ovum and Embryo before the Third Week after Conception, with a description of some early Ova: Part I

By Allen Thomson, M.D.,F.R.C.S.E., and Lecturer on Anatomy and Physiology. Parr I.


The anatomy of the human ovum, comprehending the fetus and the membranes in which it is inclosed, has been studied with t care and success in its various stages subsequently to the third month of pregnancy, both by anatomists and by practitioners of midwifery ; but it is generally acknowledged that its minute structure in the first stages of its formation, or in the first three or four weeks after conception, is very imperfectly known.

The main obstacles to obtaining this knowledge are, first, the difficulty of procuring specimens for examination, in consequence of the comparative rarity of abortion in the first three or four weeks of pregnancy; and second, the frequent unnatural condition of the ovum in cases of abortion. The striking analogy that has been ascertained to exist in the general phenomena of development of the ovum in very different classes of animals has, from the great success which has recently attended the investigation of this subject, prevented our feeling the want of knowledge of the structure of the human ovum from direct observation, so much as might otherwise have been the case ; for the analogy demonstrated to exist in the greater number of the more important phenomena, has entitled us to extend its application to the whole history, of development.

Great, however, as the similarity in the general laws of foetal formation may appear to those intimately acquainted with the subject, there are some persons who doubt the justness of the application to the human species of the general laws of development established by the observation of animals solely ; and others who regard (though erroneously) the development of the human ovum as differing widely from thatof the loweranimals. Thereare, it must be allowed, several important particulars in respect of which the development of Mammalia differs from that of birds, and the deveopment of the human species from that of both. On these grounds, if on no other, all will probably agree that, in matters in which such minute and accurate observation is required, it is highly desirable to multiply as much as is possible the number of careful descriptions of the contents of the human gravid uterus, and of the pro- ducts of abortion, in the early stages of pregnancy.

It is in the hope of supplying one or two of the deficient links. in our present knowledge of the condition and structure of the human ovum in the first stages of its formation, that I am indeed to offer the following account of some ova which I have had an vee of examining with attention.

I shall premise the history of my own observations by a short record of instances of early human ova which have been described by others, so far as they have come under my notice.

All those who have paid attention to the subject now under consideration are aware that it is extremely difficult, if not indeed quite impossible, to determine exactly the period, after conception, at which, the human ovum arrives in the cavity of the uterus. Making full allowance for the usual loose manner of calculating the date of pregnancy in most instances of abortion, and the difficulties generally opposed to our obtaining a knowledge of the time of conception in instances of sudden death; there is every reason to believe that in the human species, as is well known to occur in several kinds of animals, there is considerable variety as to the time of the descent of the ovum, and also as to the rapidity of its evolution after its first arrival in the cavity of the uterus.

It appears doubtful whether the ovum of the human species has ever been distinctly observed in the uterus before the tenth or twelfth day after impregnation. There are several instances om record, it is true, in which the uterus of the human female has been carefully examined within eight days after the occurrence of conceptions but it does not appear that the ovum has been seen distinctly in any of these cases.

Professor Baer gives an account[1] of the examination which he made of the pregnant uterus of a female who committed suicide eight days after impregnation. The principal signs of recent conception were present in this instance: a corpus luteum, in its first stage, was observed in the ovary, and the substance of the decidua effused on the inner surface of the uterus, had begun to be permeated by blood-vessels passing into it from the mucous membrane of the uterus ; but no ovum was perceptible in the uterus, though sought for with great care.

Edward Weber published in 1830[2] the history of the examination which he had made of the uterus of a woman 22 years of age, who committed suicide on the seventh day after she had been visited by her lover. All the marks of recent conception were present, The uterus, tubes, ovaries, and round ligaments were all turgid with blood; the size of the uterus and ovaries was increased one of the Graafian vesicles was burst, and another was enlarged, prominent and vascular ; and a layer of a substance like organizable lymph covered and intervened between the enlarged villi of the internal membrane of the uterus, which was probably the commencing decidua. I have not had an opportunity of seeing the original dissertation referred to in the note below, but only extracts from it in H. EK. Weber’s edition of Hildenbrandt’s Anatomy,* and in the Saltzburg Medizinische Chirurgische Zeitung.t The statements made with regard to the presence of an ovum in the uterus in this case differ in the two extracts to which I have just referred ; for in the first H. E. Weber makes no mention of an ovum, and says, ‘ It appears doubtful whether here an ovarian vesicle had recently discharged itself, or whether it was only in the act of doing so ;” while in the Saltzburg Journal it is stated, that, “‘in the middle of the posterior internal surface of the uterus, at a place where the membrane and decidua were redder than in other places, there was observed a small round transparent body, smooth on its free side, but at its margins united with the surrounding villi, and of a mother of pearl colour. In the middle of this there appeared a round, yellowish, and transparent point which had the appearance of a smaller vesicle inclosed in the larger. The smaller vesicle lay near the surface of the larger, so as even to press it out; at which projection there was also a small dark spot, such as Baer has represented in the ovum of the dog.” The external vesicle the author considers as the ovum, and the lesser as the umbilical vesicle.

Baer, in referring to this case, states, that there existed a doubt as to the presence of an ovum.

Sir Everard Home and Mr Bauer § believed that they had discovered a minute ovum and embryo in the uterus of a girl, who died on the seventh day, as was supposed, after impregnation. The case now alluded to has been so often quoted and discussed, that it is unnecessary for me to enter into its details. I shall only remark, that the examination of the uterus, which appears to have presented the principal signs of conception having occurred, was undertaken at a time when this subject was less understood than at the present day, and does not appear to have been conducted with that minute accuracy which the delicacy of such an investigation demanded.|| Admitting that impregnation had occurred at the time supposed, there are several circumstances which seem to show, that the small body described by Mr Bauer was not a foetus, as he conceived it to be. Its lying near the neck of the uterus, its position within the cavity of the decidua, and not, as more probably ought to have been the case, imbedded in that substance, and the form of the body itself, which was described as Professor Baer remarks, (loco citato,) on Mr Bauer’s drying the ovum on a plate of glass in order to preserve it, that he might just as well have boiled or roasted it. 122 Dr Allen Thomson on the showing the heart and liver of an embryo, (in place of the chorion and yolk of an ovum, which we should have expected to meet with, induce me to place no reliance on this observation.

Vol. iv. p. 466, in a note. + For 1832, Vol. iii. p. 10.

+ Vorles. ub. Entwick. Vol. ii. p. 270. § Philos. Transact. 1817, p. 252.

I may take this opportunity of mentioning, that, a few months ago, I was permitted, through the kindness of Dr J. Y. Simpson, to examine the uterus of a young woman murdered by her husband in a fit of jealousy, apparently, as some signs at least seemed to indicate, within a short time after impregnation had taken place. This woman had been married for several years, but without haying had any children. On opening the uterus, a decidual membrane, in the first stage of its formation, was found to occupy the cavity of the uterus, which was somewhat enlarged ; and a large corpus luteum, exhibiting the plicated structure in great perfection, and having cavity in its interior, projected from the surface of one of the ovaries ; but no ovum could be found in the cavity of the uterus or Fallopian tubes. I observed, indeed, that the fimbriz of the Fallopian tubes presented a singular puckered appearance, which had contracted the mouth of the infundibula to such a degree, that a small probe only could be passed into them, and had thus formed a bag at the end of each tube containing a number of small gritty, calcareous-looking particles. Such a puckering must, I should think, have acted as an impediment to the entrance of an ovum into the Fallopian tubes.

I have said that no ovum was observed in this uterus nor in the Fallopian tubes; but I ought not to omit the mention ofa small and delicate vesicle, about one-sixth of an inch in diameter, which was seen imbedded in the substance of the decidua, not far removed from the opening of the Fallopian tube, on the same side of the uterus as that on which the ovary presented the corpus luteum. This vesicle was of so delicate a consistence, that it was destroyed as soon as touched; and I am therefore inclined to think it may have been no more than a small spherical cell in the decidua, for neither a flocculent chorion, nor any inner vesicle corresponding to the yolk, were perceptible.

Dr John Reid has recently made an examination of the uterus of a woman who died suddenly in the waiting-room of the Royal Infirmary of Edinburgh. The existence of a corpus duteum in one of the ovaries and the decidua in the uterus make it probable, that conception had taken place a short time previously to her death ; but he was not able to discover any appearance indicating the pre~ sence of an ovum in the uterus or Fallopian tubes.

In a paper on the early condition of the ova of Mammiferous animals, published in the Philosophical Transactions of London,* Mr Thomas Wharton Jones has described a very small human ovum sent to him by Dr Mackenzie of Glasgow, and which I ain inclined to regard as one of the earliest, if not the very earliest, human ovum that has been accurately described, the record of which has come under my notice.

Dr Mackenzie “ considered the ovum as three or four weeks old, the lady who passed it having missed one menstrual period, and thinking herself four weeks gone.” But unless we suppose that the development had ceased or been much retarded, it 1s not probable that the ovum was of so old a date as Dr Mackenzie believed. When I speak, therefore, in these pages, of the age of any product, I beg it to be understood, that, unless otherwise expressed, I refer rather to the degree of advancement of the parts of the embryo, than to the alleged or supposed date of impregnation.

The ovum in question was found in the substance discharged, lodged towards the side of the decidual covering, and was nearly of the size of a large pea before being put into spirits. One side of the exterior surface of the ovum was smooth, and the other covered by the villi of the chorion. The whole cavity of the chorion was filled with a fine gelatinous cellular tissue, imbedded in which, towards one extremity of the ovum, was a small round body. This was evidently the vesicular blastoderma, destitute of any vitellary covering. ‘ The embryo had not appeared, though the vesicular blastoderma was undergoing the preparatory changes.”

The next ova in point of advancement to that described by Mr Jones are two of those of which I shall give the history in the sequel of this paper. All the others described by authors with which I am acquainted appear to belong to a more advanced period, when the parts of the foetus and its membranes are formed.

Dr Pockels of Brunswick * gave, in the year 1825, a very valuable and elaborate description of the condition of the human ova in their early stages, in a paper which, notwithstanding some errors into which the author fell, may be regarded as one of the best accounts of the early ovum that has yet been published.

Among fifty ova which Dr Pockels had the opportunity of examining, there were four only which had been passed in abortion between the eighthand thesixteenth dayafter conception, and which, according to his belief, were at the same time well formed.

Dr Pockels speaks of the embryo as existing in an ovum of eight days after conception, making mention also of the rudiments of the posterior extremities, and of a large vesicle placed near the embryo, which vesicle, according to a theory peculiar to himself, he conceives, gives rise to the amnios by receiving the embryo

Oken’s Isis for 1825, Heft xii. I regret that, having lately lost the copy of Dr Pockel’s paper from the Isis, which I possessed, and as another copy is not to be found in Edinburgh, I can only speak of his observations from my own recollection, and the citations of others. Fe aN eae eee ee ee ee ee a el Tek ol ee ‘f q Ri tian Web teed a ems aR rey a 124 Dr Allen Thomson on the

within it. Dr Pockels also describes ova of ten and twelve days after conception: but it appears to me manifest, from a minute inspection of his excellent drawings, that some of these very early ova are altered from the natural condition, and that others belong to dates considerably later than those given them by Dr Pockels—an opinion in which I was confirmed by an actual inspection of some of the specimens in the year 183], when I had the pleasure of visiting Dr Pockels at Brunswick, I may here remark, that the opinion advanced by Dr Pockels, that the amnios of the human foetus consists of a large and distinct vesicle, which is at first unconnected with the embryo, and that the embryo acquires its proper amniotic covering by sinking into the interior of this vesicle, is wholly at variance with the analogy of all animals, and, indeed, in the present advanced state of our knowledge of this subject, wholly untenable. Upon this subject, however, I shall reserve my farther remarks for the sequel of this paper. Dr Pockels has described and figured most accurately the appearance of the umbilical vesicle or yolk sac, at the time when it is attached to the embryo by a very short pedicle; and he also has described another vesicle placed nearer the caudal extremity of the embryo to which he gives the name of erythroid vesicle, regarding it as a peculiar production in the human ovum ; but Baer and Coste have shown, in my estimation satisfactorily, that this vesicle corresponds with the allantoid or urinary vesicle of other animals,

M. Coste,* trusting to the observation of Sir E. Home and Mr Bauer, already referred to, the validity of which he fully admits, founds some of his views respecting the early condition of the human ovum upon this observation. He has also given a very accurate description, accompanied by drawings, of a very early ovum which he dissected.

The size and shape of this ovum were those of a small hazelnut: the chorion was distinctly villous. The body of the embryo was perceived on the chorion being divided ; it was “‘a line and aquarter long, and a line and a-half broad,” of an oval shape, and presented, on the abdominal surface, an elliptical opening. half a-line long ; through this opening there were fixed, to the abdominal surface of the embryo, the pedicles of two vesicles, one nearly opposite to the middle of the body, the other nearer to the caudal extremity. These parts are all well shown in the 4th figure of Plate 3. of M. Coste’s work, executed by M. Chazal, whose talents for anatomical drawing are sufficiently well known. M. Coste has shown, I think satisfactorily, that one of these vesicles corresponds to the umbilical vesicle, and the other to the allantoid membrane.

Cours sur le Developpement de Homme et des Animaux, &c. Vol i. Paris, 1837. See particularly p. 189, et seq. 3 et Oa

While M. Coste has corrected one or two of the errors into which Dr Pockels had fallen, and has replied successfully to the critique of his work made by Messrs Velpeau and Raspail, he seems to me to have himself been led into important errors upon several points. He supposes that the amnios of the human fetus, as well as of other mammiferous animals, is first formed by the detachment or raising of the outer covering, or epidermis of the foetus. Surely in advancing so strange an hypothesis, M. Coste must have overlooked many observations by which it may be proved that the amnios is formed by the union of the cephalic and caudal folds of the serous layer of the germinal membrane in the Mammalia, nearly, if not exactly, in the same way as was shown to take place in birds by Pander, the founder of the modern history of development. Of this mode of formation I have myself had abundant proofs in the ova of the cat, sheep, and rabbit, in all of which animals I have examined the amnios in its open state before the union of its cephalic and caudal folds. M. Coste seems, in his description of the formation of the amnios, to have been misled by the very rapid changes of appearance which that membrane presents at different stages of development, its being completely formed in the human ovum at a very early stage of advancement as compared with birds,—its close proximity at first-to the surface of the body of the embryo,—and its subsequent rapid, and great enlargement, when it leaves the surface of the embryo, and forms rather a lining to the chorion: the last being one of the circumstances peculiar to the development of the human ovum, which, T am inclined to think, is frequently connected with its abnormal condition, and which has very frequently led those who have described it into error.

In subsequent parts of his work the confusion introduced by M. Coste’s considering the chorion and vitelline membrane as synonymous, is altogether surprising in one who has enjoyed such excellent opportunities of studying the subject of development, and who has given to the public several new and valuable observations regarding this branch of science.

The age of the product of conception described by M. Coste was not known with certainty. Sufficiently aware of the fallacies to which the determination of the age of aborted products is exposed, he is induced, by comparing it with those described by Dz Pockels, and from other circumstances, to regard it as of a date between sixteen and twenty-five days after conception ; with which calculation the structure of the ovum and fetus appears to correspond. At the same time it must be remarked, that, according to the history of the case, one month is the lowest age that could be assigned to this product, and this discrepancy between its apparent and its computed age is only another proof of the extent of the variations to which the progress of development of the human ovum is subject in the early periods of gestation. :

M. Velpeau, in his work on Human Embryology,* states, that he has had an opportunity of examining three human ova which were not more than twelve days old. Their volume was equal to that of a large pea, and they resembled one another exactly in form. The first presented the appearance of a simple free vesicle with a villous covering ; the second exhibited some appearances, though doubtful, of the formation of an embryo; and the third, M. Veleee with reason avers, is one of the most valuable specimens of the

uman ovum that has been seen. This ovum was obtained from a midwife who aborted on the thirteenth day after conception. This lady had previously had six children, and as, upon the occasion referred to, her husband returned to her, after an absence of six weeks, the day before that from which conception was dated, there is every reason to regard the age of this specimen as having been accurately established ; a circumstance which, joined to the apparently perfectly natural condition of the parts, gives to this observation a high degree of importance. The chorion was villous. The umbilical vesicle, and the amnios inclosing the embryo are all represented in M. Chazal’s beautiful drawings ; + but the description of the ovum is so meagre that we are left altogether in the dark regarding the more interesting points of structure which might have been elucidated by a sufficiently minute and accurate examination.

M. Velpeau’s observations on the early state of the amnios, as given at page 25 of his work, show that his notions on this point are by no means precise.

In a recent number of the Lancet, | the late Mr Miller, an ardent student of anatomy, has described a very early human ovum, the external diameter of the chorion of which was only five lines ; but although it is apparent, even from the imperfect drawing with which Mr Miller’s letter in the Lancet is accompanied, that the specimen is valuable as affording a natural view of the parts in the earliest condition of the foetus; yet his description of these parts is extremely defective, and contains several serious errors. Mr Miller describes, for example, the germinal disc or spot as apparent on the external surface of the chorion, while the foetus enveloped in its amnios lies within, and he regards the amnios and allantois as formed from one membrane,—statements which those possessing an acquaintance with the laws of foetal formation know to involve impossibilities.

Professor Mayer of Bonn has described and figured in his embryo. 127 Icones Selecta, * a human ovum, about halfan inch in diameter, and said to be three weeks old. ‘The fcetus is represented as inclosed in its amnios, which was not far removed from the surface of its body; and the umbilical vesicle is shown attached to the body of the embryo, by a very short, but at the same time a narrow duct.

_ * Ovologie Humaine, &c. Folio. Paris, 1833, p. 77. + See Velpeau’s Work, plate i. figs. 1 and 2. + Lancet, 1837-8, Vol. i- p. 258. ROT Sr ae

Professor Miller, in his Jahresbericht of the progress of anatomical and Physiological Science for the year 1833,+ gives an account of an early human ovum of 7—8 lines in diameter, which, from the history of the female aborting it, might be either nine or thirty-four days old. The embryo was 24 lines long, inclosed in an amnios, which adhered closely to the surface of its body. The umbilical vesicle, 14 line in diameter, was united to the intestine. by a very short duct, or rather by a slightly contracted portion three-fourths of a line in length.

I shall conclude this notice of the statements of authors respecting the structure of the human ovum in the first three weeks subsequent to conception, by a reference to the observations of Baer, contained in his interesting lectures on development, quoted in the commencement of this paper ; in a few pages towards the conclusion of whicht there is embodied a short but comprehensive and accurate account of most that was known at the time regarding the early condition of the human foetus; and to which some interesting original observations are added by the author.§

In the beginning of this paper I have mentioned the observations of Baer on the state of the uterus, in a woman dying eight days after conception. According to this observer it is probable that the period at which the ovum enters the uterus is subject to considerable variation in the human species, as well as in some of the lower animals. Baer conceives that the formation of the embryo may vary in the time of its commencement from the seventh to the twelfth day, allowing that the little body described by Sir E. Home and Mr Bauer was an embryo, which he is much disposed to doubt.

Baer also holds it as established that no human ovum has yet been observed in the cavity of the uterus of which the chorion was not more or less covered with flocculi.

The ovum consists at first of two vesicles, the external, constituting the chorion, the internal, the yolk, upon the surface of which the rudiments of the embryo are first formed when it-has received a covering from the germinal membrane, which thus forms the yolk-sac or umbilical vesicle. ‘The gradual separation of this ve~ sicle from the foetus by the contraction of the umbilical duct, which Baer regards as probable, is demonstrated by the specimens which T am about to describe.

“ Icones Select Preparatorum Musei Anatom. Bonon. Tab. vi. figs. 3 and 4.

{ Miiller’s Archiv. 1834, p. 8.

£ Vorlesungen uber Entwickelungsgeschichte, Vol. ii. p. 264.

§ The "Studien zur Entwickelungsgeschichte des Menschen,” to which Professor Baer refers, as giving a fuller account of his investigations concerning the human ovum, I regret that 1 have not had an opportunity of secing ; nor the extract of them contained in Siebold’s Journal fur Geburtshilfe, Vol. xiv. heft. 3, Leipzig, 1835, from which some notices are taken in the first volume of the British and Fong: reign Medical Review, p. 238.

Baer has also shown, by the examination of a human ovum of fourteen days after conception, the minute description of which I regret I have not access to, that the germinal membrane or blastoderma separates, like that of birds and quadrupeds, into “ an animal and vegetative layer,” (1. the serous, and 2. the vascular and mucous layers of Pander,) from the first of which he holds that the amnios is formed in man and in the Mammalia generally, exactly in the same manner as is well known to occur in birds ; and he very ingeniously suggests, that the false amnios (of Pander) furnishes an external serous covering to the foetus, which soon becomes irregularly disposed over the surface of the amnios and yolk. This I have frequently observed, and I think it probable that this false amnios may be the occasion of several errors which have been committed in the description of the membranes of the early ovum.

In the last place, Baer has shewn that the allantoid membrane, or at least the inner portion of the urinary membrane, has in the first weeks of gestation, the form of a small pyriform vesicle, attached by its pedicle or urachus to the caudal extremity of the rudimentary intestine, and not, as many, and among others M. Velpeau, have endeavoured to prove, an extended membrane lining the whole space between the chorion and amnios.

In two abnormal human ova I have met with the vesicular ap“aa of the allantois described by Baer; but I cannot say that have been, like him, successful in showing it in all ova below the age of five weeks, that I have had an opportunity of observing. This vesicle has been well described by M. Coste, and it appears to be the same with that called by Pockels the Vesicula Erythroides.

  • I ought here to refer to some other authors who speak of the carly condition of the human ovum; Dr John Burns’ ‘+ Observations on the Formation and Structure of the Human ovum, in the second volume of this Journal, p. 1, 1806.” Mr Stanley’s ** Case of Death by Poison, wherein impregnation had taken place, and-the ovum was detained in the ovary,” in the 6th volume of the Medical Transactions of the College of Physicians of London, p. 414, 1820; and the remarks in Dr Robert Lee’s interesting paper on Double Uterus, and the Mombranes of the Human Ovum, in the 17th volume of the Medico-Chirurgical Transactions of London, p. 474, 1832. But though in these several papers, and more particularly, in the last, there are very valuable remarks on the condition of the early human ovum, there is a want of that precise information regarding its structure to which our attraction is at present directed. I have not had an opportunity of seeing Professor Seiler’s work on this subject.

Ovum, No. I.

Plate II. Figs. 1, 2, 3, and 4.

This ovum I was kindly permitted to examine by ProfessorCumin of Glasgow in the course of ast autumn. There are no certain data from which the age of this product can be established. It was passed in abortion six weeks after the last menstruation ; but from its size can scarcely be regarded as more than twelve or fourteen days old, if so far advancedevenasthat period. Itsexternaldiameter, when freed from a small quantity of adhering decidua, was ,°, of an inch; but the specimen had undergone some contraction from being immersed in acetic acid, and diluted alcohol. The chorion presented a slightly villous appearance on its external surface, the villosities being rather longer and more thickly set at one side than the other.

On carefully opening the chorion, which consisted of one layer of membrane only, an opaque vesicle, viz. the yolk-sac, or umbilical vesicle, was observed in the interior, and on one side of this there lay a minute body, which could be no other than the rudimentary embryo.

The umbilical vesicle and embryo did not fill the cavity of the chorion completely, the diameter of the vesicle being only very little more than half that of the chorion. The embryo was a line in length, and nearly 5 of an inch in thickness. The space intervening between the outer surface of the umbilical vesicle, and the inner surface of the chorion, was occupied by a thin tenacious web of albuminous filaments, probably formed by coagulation in the spirits ; and towards the back of the embryo, and on the opposite side of the umbilical vesicle, this substance was more dense than elsewhere, and united both the fcetus and umbilical vesicle firmly to the chorion. I have more than once remarked this union, which opposes some difficulty to the examination of early ova.

I could not distinguish any external membrane of the yolk-sae, or umbilical vesicle corresponding with the vitelline membrane ; this part being covered by the granular germinal membrane or blastoderma only, which appeared to be separable into several layers. I could not see any blood-vessels on the yolk-sac, though an irregularity of the surface seemed to indicate their existence.

The embryo was in the very earliest stage of its development, for it lay with its abdominal side nearly flat on the surface of the umbilical vesicle, the abdomen presenting no appearance of intestine as yet, but merely a long and shallow intestinal groove, which formed a common cavity with the interior of the yolk-sac. The corrugated appearance of the dorsum of the embryo represented in

Fig, 4 is probably not natural, but produced by the action of alcohol or by other causes. Around the intestinal groove, the germinal membrane of the foetal parietes was continuous with that on the surface of the yolk-sac. One extremity of the embryo, apparently corresponding with the cephalic extremity, was considerably thicker than the other, and had a rounded form, as seen in Fig. 4, an appearance which differs somewhat from that which I should expect to find in a perfectly natural condition, and which in this instance I believe to have been the effect of accident.* A more opaque and expanded portion between the cephalic extremity of the embryo and the surface of the yolk appears to me to indicate the place of a rudimentary heart.

This ovum, then, appears to be intermediate in its advancement between that to which I have referred above, as being described by Mr. T. W. Jones, and those of Velpeau, Pockels, and others, in which the foetus had attained a more advanced stage of development. With the exception of the degree of corrugation or alteration in the form of the dorsal part of the foetus to which I have referred, the appearance of the ovum seems natural, and this more particularly as respects the relative size of the parts to one another. It affords an example of the earliest condition of the human feetus which has been yet observed ; when in all probability, the primitive folds have just united to form the vertebral canal, and when the intestinal folds of the mucous and vascular layers of the germinal membrane have not yet by their union given rise to the simplest form of intestine. The circulation of the blood might be begun or about to commence.

This specimen shows also two remarkable peculiarities of the human ovum ; Is¢, the very small size of the embryo in the earliest stages of development, as compared with that of other animals, and 2d, the very early period at which the yolk is inclosed by a complete covering of the germinal membrane,—a circumstance in which it bears some analogy to the ovum of some of the aquatic Batrachia, as of the common newt.

Ovum, No. II.

Plate II. Figs. 1, 2, 3 and 4.

The second ovum which I shall describe is in the possession of Dr John Reid of this city, who kindly permitted me to examine it.

It was procured from the uterus of a woman, aged 20, who died after an illness of a fortnight’s duration. This person was married six weeks before her death, to a man with whom she had cohabited for a year before their marriage, and by whom she had had one child. The last menstruation ceased on the 24th of May 1838 ; her husband, a labourer, visited her at the end of every week, and

This appearance I have represented as I saw it, being afraid of attempting to remove it by touching the fetus with a small instrument. I must here take the liberty of stating as an apology to the reader, for the imperfection of my account of this ovum,.that the examination of it was made in a bad light, and when, being from home, I had none of those delicate instruments or other aids by me which I am in the habit of using in such researches. Human Ovum and Embryo. 131 her death took place on the Ist of July, that is, five weeks and one day after the first visit of her husband, succeeding to her last menstruation. But the whole size of the ovum and structure of the foetus do not warrant us in considering the ovum as dating from so early a period as five weeks before her death: and three weeks even appear to me too long a period ; unless, indeed, it be supposed that the illness under which this woman laboured for a fortnight before her death had put a stop to, or retarded the development of the ovum, which is not improbable from the large size of the chorion, as compared with the foetus and umbilical vesicle. When we consider the size of the ovum, and some other circumstances, * there seems some reason to think that the commencement of her illness and her impregnation may have been connected with one another, or have been nearly at the same period of time. From these considerations, I am inclined to regard the ovum as probably dating little more than fifteen days from conception.

The uterus was carefully removed from the body, and all the parts attentively examined by myself, in company with Dr Reid and Dr J. Y. Simpson, before they had been immersed in alcohol. The size of the uterus was nearly one-half larger than in the unimpregnated condition. The left ovary presented the most perfect specimen of the corpus lutewm in process of formation, which I have ever seen in the human female. A considerable cavity existed in the interior of the corpus luteum, the aperture of which on the surface of the ovary was quite closed. The yellow substance of this body formed rather a regular plicated lining to its cavity than a solid, rounded, and projecting mass.

On cutting through the uterine parietes, the decidua adhering to the inner surface of the mucous membrane presented, throughout its whole extent, small blood-vessels, which passed from one membrane to the other. The exterior of the decidua vera measured about two inches in length ; the thickness of its walls was generally about one-fourth of an inch. The cavity of the decidua was occupied by the usual fluid, and from the posterior wall of the decidua vera there projected forwards the swelling of the decidua reflewa, containing the ovum imbedded in its substance. This swelling of the decidua reflewa was about three-fourths of an inch in diameter. On cutting through this membrane, the villi of the chorion made their appearance.

The greatest diameter of the ovum (or chorion) measured sixtenths of an inch, the lesser four and a half tenths. The villi of the chorion, as is seen in Plate II. No. II. Fig, 1, were considerably more numerous and more branched on one side than on the other.

This woman is stated to have died with the symptoms of chorea.

The examination of the interior of the ovum was unavoidably postponed till after it had been kept in alcohol for some time. On cutting through the chorion, which seemed to be composed of one layer only, its cavity, No. II. Fig. 2, was seen to be filled by a web of fine shreds of a substance which I mentioned in the last described specimen, and the same, I presume, as that to which M. Velpeau has given, in ova of a later date, the name of corps reticulé, imbedded in which, and situated towards one extremity of the chorion, was the embryo with its yolk-sac. Both embryo and yolk-sac were attached to the interior of the chorion by a denser portion of the reticulated substance, and much in the same manner as in the ovum, No. I., that is, the dorsum of the foetus, and the pag side of the yolk-sac being the most attached portions.

The length of the foetus was nearly one-tenth of an inch; that of the yolk somewhat less, or about one-twelfth.

The foetus, as in the ovum first described, was not united to the yolk-sac by a pedicle or umbilical constriction, but lay nearly flat, with its abdominal side opposed to the surface of the yolk, there being a distinct continuity between the germinal covering of the yolk and the sides of the foetus. The foetus is in the earliest stage of development. The vertebral canal, in which the cephalic and caudal extremities are without difficulty distinguished from one another, are considerably more distinct than in the first described ovum. By viewing the foetus at its extremities, I could also perceive that the groove of the vertebral canal was (whether from ac« cident or naturally I cannot decide) open more or less in its whole extent. Below this rudiment of the cerebro-spinal axis, an intestinal groove, more perfect than that which was seen in No. I., existed; and from the accidental rupture of a small portion of the caudal extremity of the embryo, I was enabled to see through the intestinal groove into the interior of the yolk, with which the intestinal groove formed a common cavity. Below the cephalic extremity of the embryo, and between it and the yolk, an irregularly shaped mass was seen, which may indicate the place of the heart, if it is not itself that organ.

There was neither any allantoid membrane nor amnios. I would call the attention of the reader, however, to a portion of fine membrane which adhered to the notch between the foetus and yolk at the cephalic extremity, and which had the appearance of a portion of the reticulated body, denser and more membranous than the rest, which turned slightly over the head of the embryo, and caused its firm adhesion to the inner side of the chorion. Iam inclined to believe that this piece of membrane may be a part of the cephalie fold of the serous layer of the germinal membrane Human Ovum and Embryo. 133 which forms the amnios. The remarks of Professor Baer, in his work already referred to, have satisfactorily disproved the views entertained by Pockels and Coste respecting the mode of formation of the amnios; and although no direct observations have as yet been adduced, in which the ununited state of the cephalic and caudal folds of the amnios has been seen in the human foetus, there can now be no doubt that, in this respect, the human ovum does not differ from that of other animals.

I was not able in this example to perceive the omphalo-mesenteric blood-vessels on the surface of the yolk, although the same marks of which mention was made in the description of the first ovum, seemed to me to indicate their presence.

The ovum, then, which is figured in No. II. affords an example, in which, although the development of the chorion is somewhat advanced, the embryo itself, and the parts immediately connected with it, are in a very early condition. Though the embryo and yolk-sac of this ovum are smaller in size than in the ovum No. I. the more distinct form and greater consistence of the parts incline me to believe that they, as well as the chorion, were in a slightly more advanced stage of development. We have here the yolk covered by the layers of the germinal membrane forming the yolksac or umbilical vesicle; the embryo consisting principally of the rudiments of the cerebro-spinal axis and the intestinal groove, and in which it may be supposed that the heart also has been formed in its first or simplest condition,—a state of the parts, which, if such a comparison can be made, approaches to that existing in the incubated egg of the fowl at the thirtieth or thirty-fifth hour.

Ovum, No. III.

Plate II. Figs. 1, 2, and 3.

The last of the ova which I shall now describe belongs to a period considerably later than either of the preceding specimens. It was given to me in 1834, by Mr Sidey of Edinburgh, to whose . kindness and scientific zeal I have frequently been indebted ; as having been passed six weeks after the end of the last menstrual period, by a person who had previously born children. In so far as the ovum, as a whole, is concerned, it is manifestly one of the date of five or six weeks; but it is one of those products so frequently met with in abortions, which, from a want of correspondence in the development of the membranes of the ovum and the parts of the fetus, some parts of the product haying been arrested in their development, may serve for the illustration of the structure at an earlier period than that at which the ovum is passed. The foetus, in fact, and umbilical vesicle of this specimen form a link in the series of early ova not far removed from those previously described.

The chorion, about an inch wide in its longest diameter, presented a considerable number of villi of moderate size, and, as usually happens, in greater quantity on one side of the ovum than on the other; that is, on the side on which the placenta would afterwards have been found. ‘The interior of the chorion was filled with a flocculent fluid, and the embryo with the umbilical vesicle adhered to the inner side of the chorion, as seen in No. III. Fig. 2.

The foetus, represented magnified ten diameters in Fig. 3, was about one-eighth of an inch long, its body nearly one-thirtieth of an inch thick. In this example the embryo consists of the rudiments of the head and vertebral column, forming the head and trunk of the body. There is as yet no appearance of the extremities. The vesicles of the brain are slightly visible, and the sacral part of the vertebral column is prolonged at the caudal extremity. I could not perceive the rudiments of the eye or ear, which, nevertheless, I believe, must have been present. The heart hung forward from the body of the embryo, without any covering, and having the simplest form belonging to that organ in the early stages of development, viz. a curved tube, one extremity of which, corresponding to the bulb of the aorta, was attached to the forepart of the neck, while the other extremity, corresponding to the auricular part connected with the veins, was attached to the body of the embryo farther back. In a subsequent paper I hope to be able to show the successive changes by which, in the human fetus, this simple incurved tube, like that of birds and quadrupeds, is gradually converted into the perfect heart of advanced stages of development.

The intestinal canal formed a simple and straight tube. The mouth was open, but no anus was yet formed at the caudal extremity. In the middle part of the body of the embryo, the intestinal tube opened by a wide aperture into the umbilical vesicle, which now no longer lies below and supports the foetus, as in the two previously described ova, but begins to be separated from it by a more constricted portion, which would afterwards have been elongated and narrowed into the small pedicle or duct by which, in the fourth and fifth weeks, and at a later period, the umbilical vesicle is attached to the intestine. A few of the omphalo-mesenteric vessels were visible on the surface of the umbilical vesicle.

The posterior extremity of the intestine opened into, or rather was continuous with, a tube, by which the embryo was firmly attached to the chorion. This tube had the shape of a funnel, or was somewhat pyriform, manifestly constituting the urachus. It is possible that the dilated part immediately adjacent to the foetus may have contained the pyriform vesicle which Baer considers as the allantois, although I was not able in this instance to satisfy myself of its presence. I have, however, in two abnormal ova, observed the vesicle described by ais as analogous to the allantois.

Two very small branchial slits were visible in the neck of the embryo, which from their position appear to be the two first of the four which exist at a later period. In a subsequent paper I shall mention human fcetuses in which I have observed four branchial slits existing at one time.

No amnios was to be seen covering immediately the body of the embryo. In the first examination of this specimen made five years ago, I thought I perceived the amnios lining closely the chorion, and I considered this as one of those examples in which the amnios had taken on a growth disproportionate to that of the fetus. Since the perusal of Professor Baer’s remarks, however, in the . second volume of his Entwickelungsgeschichte, I begin to think I may be mistaken with regard to this point. From numerous observations which I have made on mammiferous animals, I am satisfied that in them all, the amnios is formed exactly in the same manner as in birds; and from some observations which I have lately made in human ova, I am convinced that they form no exception to the general law first established by Pander. I may here briefly mention, that although I have never as yet in the human ovum, found the cavity of the amnios open posteriorly, before the meeting of the cephalic and caudal folds of the serous layer of the blastoderma, I have remarked after the completion of the formation of the amnios, the remains of the false amnios (of Pander) adhering at the point of junction to the outside of the amnios itself, an appearance which I shall take another opportunity of describing more minutely.

In concluding, I may remark that the investigations of which _ I have given the history, have been undertaken under the great disadvantage of having very few specimens for examination, and 1 take this opportunity of requesting those who are so fortunate as to obtain early human ova, and do not wish themselves to make use of them, to allow me an opportunity of examining them.

In the next number of this Journal it is my intention to continue the present paper by a description of the structure of the human ovum and embryo in the fourth, fifth, and sixth weeks — after conception.


  1. Siebold’s Journal fur Gebiirtshtilfe, Vol. xiv. Heft. 3. Leipz. 1835, also in British and Foreign Medical Review, No. i. Jan. 1836, p. 238. This case is also referred to in the second volume of Baer’s Vorlesungen iiber Entwickelungsgesehichte der Thiere. 1837. 410.
  2. Disquisitio Anatomica Uteri et Ovariorum puellz septimo a conceptione die de - functe instituta. Halis, 1830.

Description of Plate II

No. I.

Fig. 1. Exterior of the ovum represented of the natural size. a. Shows some decidua adhering to the surface of the chorion. b. The chorion when that portion of decidua had been removed. Fig. 2. The chorion split into two halves, showing in the upper section the yolk-sac or umbilical vesicle, with a lateral view of the foetus lying upon it. — RIO Te I Termes a wl LOPE Ce my Steg oy), Fs Wy 186 Dr A. Thomson on the Human Ovum and Embryo.

Fig. 3. The same magnified six diameters: The foetus occupies the upper part of the figure, the cephalic extremity being”turned towards the left hand of the reader; at the lower side of the yolksac, the reticulated membrane, causing its adhesion to the inside of the chorion, is seen.

Fig. 4. The same specimen turned round so as to obtain a view of the dorsal aspect of the embryo. The cephalic extremity of the embryo is uppermost in the figure.

No. II.

Fig. 1. Exterior of the chorion as seen after it had been removed from the decidua, of the natural size.

Fig. 2. The cavity of the chorion laid open, showing in its upper part the yolk-sac with the embryo lying across it : these are fixed in the situation in which they are represented in the figure by the reticulated substance.

Fig. 3. The yolk-sae and embryo removed from the interior of the chorion, and represented as magnified ten diameters. The cephalic extremity of the embryo is uppermost in the figure, the dorsum being directed towards the reader; the open state of the vertebral canal is seen, a@ a.

Fig. 4. A lateral view of the same specimen, which exhibits, 5, the folds of. the intestinal grove and the part indicating the place of the heart, c, between the foetus and the yolk-sac; d is a piece of membrane which may be connected with the formation of the amnios. No. III.

Fig. 1. Exterior of the chorion, of the natural size.

Fig. 2. A portion of the chorion cut through and everted, so as to show its cavity and the embryo with its appurtenances adhering to the internal surface.

Fig. 3. The foetus removed from the chorion along with the umbilical vesicle and a portion of the chorion, and represented magnified ten diameters.

a. a.a. Head and body of the embyro.

b. The heart in the form of a bent tube.

c. Two branchial slits.

d. Umbilical vesicle or yolk-sac.

e. Pyriform part connecting the caudal extremity of the intestine and embryo with the chorion.

S-f: Inner surface of the chorion.

g.g- Its flocculi.

Cite this page: Hill, M.A. (2024, May 25) Embryology Paper - Contributions to the history of the structure of the human ovum and embryo before the third week after conception (1839). Retrieved from

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