The Humane Allantois Fully Discovered and the Reasons Assigned Why It Has not Hitherto Been Found out, Even by Those Who Believed Its Existence. With an Answer to Their Objections, Who Deny It Still. By Rich Hale, M. D. of Trinity College in Oxford. Communicated to the R. S. by Edward Tyson. M. D.

II. The Humane Allantois fully discovered, and the Reasons assigned why it has not hitherto been found out, even by those who believed its Existence. With an Answer to their Objections, who deny it still. By Rich Hale, M.D. of Trinity College in Oxford. Communicated to the R.S. by Edward Tyson. M.D. No point in Anatomy has been, and still is, more controverted by the greatest Masters of it, than the Existence, Shape, &c. of a Humane Allantois. I shall therefore give a true and exact account of it, as it appeared in two subjects, still by me. One of which I observed several years ago, and the other (Fig. 1st.) in March, 1695. But before I do this, it may be convenient to shew, that no Anatomist had hitherto made an entire discovery of this Membrane; and to take notice of the difficulties that have hindered such a discovery, even by those who believed the Existence of it; and afterwards answer the objections of those who still deny it. Most of the Antients indeed allow a Humane Allantois, not from their experience of it, but because they took it for granted, that Men and other Animals were alike, in the Viscera, Membranes, Vessels, &c. Hence Hippocrates says, that Twins lie in Sinus's, and that the Uterus has Cornua. Galen describes the Navel-string to consist of four Vessels, besides the Urachus, and the Allantois to be like a Pudding reaching from one Cornu of the Uterus to the other. In short, notwithstanding the Antients might sometimes dissect Humane Bodies, and although (a) Celsus, Herophilus and Erasistratus did open live Men and Women, yet it can't be found what great use was made of those opportunities: For the accounts the Antients have left of many parts, particularly of the Urachus and Allantois, (as to its Name, Figure, Site, &c.) agree only to their appearance in Brutes. I shall say nothing of the Allantois in Brutes, since it is granted by most Anatomists, to be in these Animals, and sufficiently described by Dr Needham. This excellent Anatomist also first discovered part of the Allantois in Humane subjects, but neither he, nor any other, has taken the right method of finding it entire, and 'tis no wonder they could not truly describe what they never saw. (b) Dr Needham says, that after the Amnios is cleared, and left fixed to the Umbilical Rope, you may divide by the fingers, or knife, the remaining part of the Involutura into two Membranes. The exterior he truly calls the Chorion, the interior he takes to be the Allantois. But by these ways of separation, you will presently tear the Allantois, and be able to discern only some small pieces of it. Besides, the Allantois is at first sight, so like the Amnios, that (c) many who suppose the Amnios double, and that its Coats are easily separable, have taken these pieces of the Allantois, for broken parts of one of the Coats of the Amnios. Whereas having first found the Hole whence the Urine came forth (if the Allantois is not too much torn) you may blow up the Allantois with a Pipe to its full dimensions, and then see its true Shape, the Fundus, the Crevix, the insertion there of the Urachus, its relation to the other Membranes, &c. Be the Allantois never so much torn, yet this way you may easily separate many Inches of it, from the Chorion, and Amnios. Which ease separation demonstrates a distinction of Membranes, since no double Membrane can be divided by the breath alone. Indeed Hoboken and (d) Diemerbroeck make it a very easy thing to separate the Allantois from the other Membranes, only by the fingers; but 'tis plain from their de- descriptions that they never saw one entire. Amongst other mistakes (e) Diemerbroeck says that the Urine of a Fætus lies between the Urinary Membrane and the Chorion; as though not contained in a distinct Bladder, but in a Cavity made partly from the Chorion, partly from the Urinary Membrane. I confess De (e) Graaf tells us, that by blowing with a Pipe into a Hole made through the Chorion, all the Membranes of the Secundines will appear distinct. He has also delineated an Allantois, with the other Membranes, &c. as he says he found them. Yet this (f) Fig. must have been drawn from his own fancy, and not from any preparation, for these reasons. 1st, Because, by this way of separation, you can only part the Allantois from the Chorion, but never see its true dimensions, nor any appearance of a Bladder; for a Bladder, as the Allantois is, can be shew'd only by blowing into its Cavity, or by finding it full. Yet in this Fig. no sign can be observed, where 'twas blown up, and tied, De Graaf also speaking of making a Hole only in the Chorion. Nor can this Allantois be supposed full of Urine, because 'tis not of the Shape of a full Allantois, and our Author himself calls it only the inflated part of the Allantois. However, I can't conceive how the Allantois could remain partly filled with Air (any more than it might with Urine) so long as till this Fig. was drawn, unless some Hole was tied up, whence the Urine came forth, and the Air was blown in. 2dly, Because in this Fig. the Umbilical Rope seems to run through both Amnios, and the Allantois, to its insertion on the Placenta. Whereas the Allantois is nowhere perforated by the Umbilical Rope, nor does it anywhere pass through the Amnios, but only runs under it, at the place of its insertion on the Placenta. If the Navel-string could be allowed to enter the Amnios at (g) I, and to pass under it to the Placenta, why should it not appear (which it does not) under the Amnios, as well as the Graaf thin thin substance of the Allantois? Again, according to De Graaf's position of the Secundines, (which is the reverse of Fig. 1st, where the Navel-string lies under the Allantois) nothing could hinder a plain view of the place where the Navel-string is set on to the Placenta. This will be easily apprehended, by supposing the part H in my 1st Fig. to lie uppermost, the Fundus G and Navel-strings being turned over; for then the Strings will run over the Allantois, as in De Graaf's Cut, and its insertion appear plain on the Placenta, which yet can't be discovered in his (g) Fig. I am sure the whole is irregular, and I take it to be fictitious. As for the Urinary (g) Membrane G it seems to be the Allantois of a Colt (where (b) Needham says, the Umbilical Rope runs through the Urinary Membrane) not less absurdly added to the Secundines of a Humane Fetus than the Secundines of a Whelp are to a like Fetus by Vesalius. Lastly, 'Tis most evident that De Graaf knew nothing of the true Shape of this Membrane, and that he had never seen one entire, because (i) he consents to (i) Needham's description of it as true, which yet is false in several particulars. For 1st, the Urinary Membrane does not cover the whole Fetus (as he affirms) but only that part of it, which respects the Chorion, and does not lie on the Placenta; for the Allantois can be extended at farthest but to the edges of the Placenta, where the Amnios and Chorion are so closely joined by Fibres, that no Membrane can come between them. Wherefore 2dly, the Allantois is not everywhere fastned to the Chorion. And consequently 3dly, the Allantois can't be of the same Shape that the other Membranes are of, nor be like the Allantois of a Colt, which contains the Fetus in the Amnios; all which nevertheless (k) Needham asserts. In short, Dr Needham had seen only pieces of the Urinary Membrane, but never an entire one, and so could only guess at the Shape, &c. of it, from what he had observed. served in Mares, and Glandulifrons Animals. He might have made a better guess at the figure, site, &c. of a Humane Allantois from that of a Whelp, which does not every where encompass the Fetus, as he observes. Bidloe in most of his Figures of the Secundines, letters some Vestigia of the Urinary Membrane, but in any of these Figures, you only see broken pieces of one, so confusedly placed, that no Idea of its Bigness, Shape, or Situation can be formed from them. I must confess that oftentimes the Membranes of the Secundines are so torn, that no Art can exhibit an entire Allantois. However, among the many Secundines that have come under the hands of Anatomists, several no doubt must have been entire enough for a fuller discovery than they have made, had it not been by their ways of proceeding (viz. by knife, fingers, or blowing under the Chorion) impossible to discover any thing plain, or satisfactory, even in the the fairest subjects. I come now to answer the objections of those who still deny an Urinary Membrane to a Humane Fetus, The difficulty of finding this Membrane is by no means an argument against the existence of it: But a Woman that dies big with Child is so fair a subject for the discovery of three Membranes, that I wonder(1) Parey having such an opportunity could find but two, if he was so careful as he says he was. The accurate Dr Tyson observed three Membranes some years ago, in a like subject. After the Chorion was divided, and laid aside, he saw two Bladders, containing Liquors of different colours, which he pressing one towards the other, did not mix, but remained distinct. This observation fully satisfied that great Anatomist, to as the existence of an Allantois; and its figure, texture, site, &c. might also have been discovered by him, had not the less curious Spectators been impatient to pass on to other parts of the Dissection. Some Some deny a Urinary Membrane to a Humane Fætus, because they suppose the Urachus to be impervious, and that therefore there would be no passage for the Urine, consequently no need of an Allantois. (m) Needham indeed says that he could never find any sign of a Cavity in the Urachus, yet is of opinion, that by blowing from the Bladder, the Air might be forced through a Humane Urachus, as easily as he has often done it through that of a Whelp. I don't understand why Dr Needham, and others should insist so much upon an apparent Cavity in the Urachus, or expect that air should necessarily pass through it upon blowing, and think that otherwise it cannot be fit for the assigned Office; since many Bodies, as Membranes, &c. will not admit Air, &c. yet let Water pass freely through them. It will not seem strange, that Water should pass through the substance of the Urachus, if we consider that the Cavity of the Urachus to the Navel is open, as appears by Inflation, or Injections, (to say nothing of those who are mentioned to have made Water by the Navel) and that the rest of the Urachus is pervious, tho' not plainly hollow, (the Urine rather soaking gently, than running through its more strait Tubes) may be gathered from hence. 1st, That the substance of the Urachus, (as well as the Cavity of the Allantois) is always found turgid with a Liquor, that in colour, taste and smell, seems Urinous. 2dly, That since the Mucous Coat of the Intestines is demonstrated to be vascular by Mr Leeuwenhoeck, therefore the Mucous substance of the Urachus may also be Vascular. 3dly, That Urine may as easily ouze through these Mucous Vessels, as other fluids run through Vascular Cartilages, and Bones, &c. or the Chyle into Lacteals, whose Orifices as Leeuwenhoeck observes, will scarce admit of Particles so big as the 100000000 part of a grain of sand; the great Cavity of the Intestines being open at the same time; or as easily as groser parts of the Semen pass the Tubes. Tubes of the Testicles, whose Cavities are not more perceptible. I am sure the Urine is more assisted in its motion by the Detrusor Urinae, &c. than any of these Fluids can be by the Heart, or other Muscles. Others will not admit of an Urinary Membrane, they thinking it would be useless, because they imagine, that when the Bladder is full, the Urine must be discharged at its Cervix, and not at its Fundus by the Urachus. But in answer to this, the Urine can never pass through the Cervix, and Urethra, unless the Abdominal Muscles contract, because we never void Urine naturally, but by the help of these Muscles, nothing less being able to force open the Sphincter Vesicae. Now it being more than probable that these Muscles never act before Respiration, no Urine can pass through the Sphincter, before the Child breathes. No reason can be given why the Abdominal Muscles of a Fetus, should voluntarily contract, since neither the Quantity nor Quality of the Urine can excite to such an action. For when the Bladder is too full of Urine, it will ouze through the lax spongy substance of the Urachus, being gently pressed by the Detrusor alone. There would arise many inconveniences from the voluntary contraction of the Abdominal Muscles of a Fetus, as voiding Faeces as well as Urine, into the Amnios, which would be more prejudicial than Sweat, &c. Yet if we should suppose the Abdominal Muscles of a Fetus to act, the Urine will however pass where it can most easily i.e. through the Urachus, which is partly open, and altogether of such a Texture, as in no wise can hinder the passing of the Urine, much less be able to resist a considerable force, as the Sphincter Vesicae can. Besides, the Urachus is not only thus qualified, for the admission of Urine, but when the Mother lies down, 'tis almost upon a Level with the Urethra, and what has once passed the Urachus, cannot return by reason of the Length, Situation, and peculiar Structure of it. Lastly, the (v) Pudendi Clausura sometimes happening in both Sexes, demonstrates that then at least, the Urine can't pass through the Urethra. Dioni not finding any Allantois, nor an Urachus plainly pervious, thinks there is no need of either, on another account. For he supposes that the Blood, which serves for the Nutrition of the Fetus, is depurated from all Excrement. But I cannot apprehend, what should make this portion of the Blood and Chyle freer from Excrement, than the rest of the Massa Sanguinea. There is indeed no portion of it, which does not contain parts unfit for Assimilation and Nutrition. Our Author would have been convinced of this error, had he ever opened Abortions of five Months old or upwards, their Bladders being always full of Urine, and some Faeces constantly in the Intestines. 'Tis difficult to determine when this separation of Urine first begins, but I am apt to think it much sooner than is generally supposed. Fig. the 3d is the Allantois of a very small Abortion, which I have still by me. Since all the parts are perfectly formed before Impregnation, not very long after Impregnation they may begin to perform their Offices. No doubt they begin as soon as there is occasion for any separation, and a separation of Urine is necessary, when the Fetus is first nourished by the Umbilical Arteries. The Existence of an Allantois is denied by some who grant an Urachus, but will have it convey the Urine to between the Amnios and Chorion. Die merbroeck's opinion is somewhat like this, only he would have the Urine lodged between the Urinary Membrane and the Chorion. These men don't consider that the Urine in this case would get into the Amnios, as well as the Succus Nutritius of the Chorion, whether imbibed from the Uterus by the Chorion, or separated by its Glands. Such a Succus Nutritius of the Chorion is granted by the Maintainers of the fore-cited opinions, as well well as by those who deny an Allantois altogether, or (a) suppose it to have a different Figure, &c. from what (a) Needh. Diemerbroeck assigns it. The Tranfudation (or Filtration through the Membranes) of this Succus seems most likely in Mares and Sows; for in a (b) Mare, the Chorion is not (b) Harv. joined to the Uterus, till she is half gone, and in a (c) de Mem- Sow it does not adhere to the Uterus till near the end of (c) Need. her going with young. But 'tis most evident that the Urine of a Humane Fetus is not contained between the Chorion and Amnios, nor between the Chorion and Allantois, from the close connexion of these Coats to one another; also from the observation of Midwives, who often find a Bladder of Water (they call it a By-Water) offering itself before the Child, whereas the Humour of the Amnios is little, and of the Chorion much less, and of another Colour, &c. at the time of Birth. This By-Water is taken notice of, as an argument for an Allantois by Mr Comper, to whose assistance we owe that the Figures belonging to these Papers appear correct. The great (d) Harvey will not allow an Allantois even (d) Harv. to Brutes, and fancies the Allantois and the Chorion to be the same Membrane, that has two names, the first from its shape, the other from its office, or number of Vessels. Yet 'tis plain from Galen and all the Antients, that they meant two distinct Membranes by the Allantois and Chorion. Dr Harvey thinks that a Fetus does not void Urine, but that the Bladder contains it, till the time of Birth. What was offered against Dion's Opinion may serve for an answer to this also. Because 'twas impossible for this diligent Anatomist not sometimes to observe an Urinary Bladder, he has thought of ways to explain such Phæno- mena without granting an Allantois. In (e) Sheep and (e) Harv. Does he had seen as it were a certain Process between the Umbilical Arteries full of Urine. This Process is no doubt the Allantois, though (f) Bartholinus calls it the (f) Lib. cap. 37. Urachus. Again, he thinks what is called by others an Allantois (if it is not the Chorion) is some Coat accidentally formed from a Reduplication of the Membranes; because (since every Membrane is double) Nature may upon a straight, lodge the Urine between a Duplicature. Yet he does not tell us how his Duplicature is to be filled, he allowing no Urachus. But, in short, this Urinary Bladder, can be no Duplicature of the other Membranes, since in all Animals it differs from them, as to Figure, Texture, and in having an Urachus, which no other Membrane has. And since every Animal that has a Bladder, must have a like necessity for a Receptacle of Urine till born, since also the Urachus is ever alike inserted in the same Species of Animals, and the Urinary Bladder constantly the same, as to Shape, Texture, Situation, &c. All the material Objections, and Difficulties about an Humane Allantois being thus cleared, I shall now consider what has been, or may be, offered against these Figures in particular, when I have first given the Explication of them. And I think there is no need of any other account thereof, since 'tis not my design to give an entire History of the Secundines, &c., or repeat what can be found in other Anatomists; but only to relate what I have discovered of an Humane Allantois, Amnios, &c., which is altogether new, or different from the Observations of others. Fig. I. Represents the Secundines of Twins, to shew the Allantois, and its Relation to the other Membranes, &c., after the parts were prepared and dried. A A A A Part of the Chorion expanded. B B B a Line, expressing the edges of the Placenta. C C C the Amnios, which is united to D. the Allantois, at E E E the Line of Union. F the Cervix of the Allantois. G a Hole at the Fundus of the Allantois, whence the Urine came forth, and where the Allantois was blown up. H Part of that half of the Allantois, which lies under the Line of Union, and immediately covered the Fetus's, unless it is supposed that the Amnios is continued under the Allantois. I I Two Stiles or Probes thrust under the Amnios. They support the Allantois, and keep open the Aperture *** of the Amnios, whence the Twins came forth. K Part of the Placenta, with some Blood-Vessels injected. L L L L the Arteries of the Navel-string filled with Red Wax. M M The Umbilical Veins filled with Green Wax. N a Communicant Artery, by means of which all the Arteries of both Navel-strings were filled at once, and the Veins were filled by one Injection in like manner. O a Pin that keeps out the Amnios, where from the edge of the Placenta it runs partly to the Line of Union, or Adhesion, and partly over the Placenta. P Part of the Chorion at the edge of the Placenta, where it runs under the Amnios on the Placenta. Q a Pin that by a thread helps to pull open the Aperture of the Amnios. R R R the Urachus, lying between the Arteries. a a a a Fibres or Vessels which fasten the Allantois to the Chorion. Fig. II. Exhibits a side-view of the same Preparation, that the Insertion of the Urachus, &c. may be better seen. N. B. That A and all the same Letters in these three Figures denote the same Parts in every one. S shews the Course of the Urachus R at F in pricked lines. T part of the Amnios raised from the edge of the Placenta, to discover the Placenta K and V. V that part of the Allantois which is below the Line of Union, near its neck F. Fig. III. Shows an entire Allantois of a very small Abortion. N.B. This Allantois was easily separated from the other Membranes between which it lay; and the Amnios remained an entire Bladder or Membrane under the Allantois. Now some to whom I have communicated these Figures object, that what is called the Line of Union can be on real thing. As to this I don't know whether the Allantois of Twins may not require such a conjunction to sustain, and keep steady a greater quantity of Urine: nor can I resolve whether the Allantois of Twins (like that of a single Fetus in Fig. 3.) may not be distinct, and separable from the Amnios, but was not discovered by me to be so, through want of skill or care. However, the reasons why such a Line was figured are these. 1. Although I used more force, with equal care, to separate the Allantois from the Amnios in this place than in any other (where nevertheless the separation was very easy) yet I couldn't divide these Membranes farther than that Line. 2. This Line seeming so regular as to divide the Allantois into two equal parts, I could not take it to be the effect of Chance, or my Separation. 3. The Part H below the Line EE was alike in Transparency to that part of the Allantois D above it. Whereas had the Amnios been still joined to the Allantois (as these Objectors suppose) the Allantois below this Line must have appeared thicker than that part above it, since the Amnios alone is much thicker than the Allantois. 'Tis easy indeed to conceive the Amnios running an entire Bladder, Bladder, or Membrane, under the Allantois, and perhaps it may be so: but I think it disingenuous to conceal what I did observe, or to make out by fancy, what I couldn't discover in fact. Others have thought this Allantois to be an Amnios of one of the Twins belonging to these Secundines. This Objection, though it may seem plausible, yet is of no force. For 1st, this Allantois is much finer to the touch, and also much more transparent, than the other Amnios; which still remains stiff, whilst the much thinner Allantois sinks upon the least blast of Air, notwithstanding the stiles II which assist it. 2dly, This Allantois had two visible Wrachus's, and it is of an Oviform Figure, somewhat like the common Cuts of a Mans Bladder (for a true Cut of a Humane Bladder I never yet saw, for it ought to be made much bigger (as it really is) at its Crevix, &c.) Also this Allantois nowhere touches the Placenta, unless at the Neck F. But on the contrary, the Amnios is of the same irregular Figure, as the Position, Motion, &c. of the Fetus require. Likewise, it covers the whole internal surface of the Placenta. 3dly, They who make this Objection must suppose some Hole in this Bladder, and in the Amnios, through which one Umbilical Rope may pass from the Placenta to the Fetus. But such a Foramen would be preternatural, because the Navel-string only runs from the Placenta to the Fetus, under a Coat taken from the Amnios, and lies with the Fetus in the Cavity of the Amnios, that is nowhere perforated. 4thly, The Hole at the Fundus G was scarcely wide enough to receive the end of a mans finger, whereas the Twins did not want six weeks of their full time. Since therefore a Fetus of near eight months could not possibly pass this Orifice, this Bladder could not be an Amnios. Nothing in these Secundines is preternatural, only some things were not before observed. Hitherto Anatomists have not allowed Twins to lie in a common Amnios. nios, but supposed each Fetus to have a distinct Amnios. The reason of this Opinion might be, that some denying any Urinary Membrane, called every Membrane they found (except the Chorion) an Amnios, and these finding two Membranes in the Secundines of Twins, supposed them to be two Amnios's. That others granting an Allantois, but not distinctly discovering it, but only two Membranes, also imagined them to be two Amnios's. Both of these taking that for an Amnios, which might really be an Allantois. But since one Chorion, and one (b) Placenta (the (i) Placenta, and (i) Chorion being ever of the same number) generally serve Twins (nay, sometimes three Fetus's) why should it seem strange, that one Amnios (at least sometimes) and one Allantois should serve the like number? I am not ignorant that (k) Mauriceau, and (l) Diemerbroeck think there is an absolute necessary for every Fetus to lie in a distinct Amnios, and that otherwise Twins in the same Membrane would grow together, and make a Monster. (m) Aquapendens further says, that all Ova Gemellifica produce some other sort of Monster. Yet 'tis most certain that Ova Gemellifica do exclude two perfect Chicken, however not both alive. (n) The Great Harvey indeed thinks it possible, that such an Ovum may produce a Monstrous Chick, if its Vitelli are contained in the same Membrane, &c. yet does not positively say it must be so. For my part I can't see any more reason why Twins in one Amnios should grow together, than that the Hands or Heels of the same Fetus should grow to its own Body. How can the Humors that lubricate a single Fetus, and help it to move, join two together? since the Humours as the same, and the parts of the same Fetus as tender as those of Twins are, and lie as close to one another, as Twins do. 'Tis very observable, that among all the Monsters we read of, there are very few, which seem to be made of two entire Bodies joined together, and that most most of these upon (o) Dissection were found to have (a) Parey but one Heart, one Liver, &c. whence 'tis most plain, Lib. 25. that these Monsters (and no doubt all others) were originally Monsters in the Ova, before Impregnation, and not so from want of an the Amnios. Yet (p) Diemerbroeck does (q) Diem. not a little boast of having first (as he thinks) found the reason why Twins must lie in distinct Amnios's. But since the matter of fact (sometimes at least as in these Secundines, where there was only one Amnios, and two regular Fœtus) is not true, his argument for a necessity of two Amnios's for two Fœtus's, will never prove valid, even where Twins, and two Amnios's are found. Indeed any part may be made to grow to any part, as we see in the cure of Hair lips, &c. but then the Fibres must be first broken before there can be any Union. Now I can't conceive what should naturally break the Fibres of the Twins in the Venerus. But although 'tis evident from what has been said, that Twins may lie distinct in the same Amnios, yet there must be as many Urachus's, as Fœtus's. In these Secundines I saw two running over the Placenta, to the Neck of the Allantois, which I communicated to some Physicians, before the parts began to grow dry. The Urachus passes under the Amnios as the other Umbilical Vessels do, and runs from that part where the Umbilical Rope is set on to the Placenta, straight to the Cervix F. S describes the course of that Urachus marked R at F in the 2d Fig. The other Urachus lay about a quarter of an Inch laterally beyond that marked R in the same Figure. I mean by two Urachus's, two long roundish Bodies, of a depressed Figure, they seemed as big as a common Knitting Needle, and were of a darker substance than the Placenta on which they lay. They appear'd in every respect like that part of the Navel-string, which is allowed by all Anatomists to be the Urachus, and in like manner shrunk in two or three days, from a Mucous substance to a meer Membrane. These two are the only entire Urinary Membranes that I have prepared. Yet in the many Secundines that have come to my hands, I have ever found three distinct Membranes easily separable. Perhaps some less curious Persons may think such discoveries as these of no use. But these may consider that hence we can better explain some Phænomena, as voiding Urine by the Navel, and the Breaking of Waters from Women half gone with Child, and tell the consequences of such accidents; as also better account for those Waters, and Bladders Midwives meet with, and direct them in their doubtful Operations, &c. 'Tis something likewise to have cleared Points thus long controverted by the greatest Anatomists, &c.