1897 Human Embryology 1

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Minot CS. Human Embryology. (1897) London: The Macmillan Company.

Human Embryology: Introduction | The Uterus | General Outline of Human Development | The Genital Products | History of the Genoblasts and the Theory of Sex | The Germ-Layers | Segmentation | Primitive Streak | Mesoderm and the Coelom | Germ-Layers General Remarks | The Embryo | The Medullary Groove, Notochord and Neurenteric Canals | Coelom Divisions; Mesenchyma Origin | Blood, Blood-Vessels and Heart Origin | Urogenital System Origin | The Archenteron and the Gill Clefts | Germinal Area, the Embryo and its Appendages | The Foetal Appendages | Chorion | Amnion and Proamnion | The Yolk Sack, Allantois and Umbilical Cord | Placenta | The Foetus | Growth and External Development Embryo and Foetus | Mesenchymal Tissues | Skeleton and Limbs | Muscular System | Splanchnocoele and Diaphragm | Urogenital System | Transformations of the Heart and Blood-Vessels | The Epidermal System | Mouth Cavity and Face | The Nervous System | Sense Organs | Entodermal Canal | Figures | References | Embryology History
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Chapter I. The Uterus

The uterus enters in the mammalia into such intimate relations with the embryo, that a thorough knowledge of its structure is neccessary to the embryologist. The treatment of the uterus in the textbooks of human anatomy is usually too brief for the requirements of embryology. These considerations make it desirable to give a some* what detailed account of the human uterus.

The uterus is the most variable organ within normal limits of the body, both as to size and structure. The virgin uterus is about three inches long and two inches wide at the upper part, where it is broadest; it weighs about 40 grammes. At the end of pregnancy it is about ten inches long and nine wide, and weighs about 1,000 grammes . The walls of the virgin or resting uterus are tense and mainly muscular; those of the pregnant organ are more spongy in texture and extremely vascular, yet at the same time the muscular layers are greatly increased, though relatively less than the vascular layer. After a pregnancy the uterus never returns to its primitive condition, and its weight does not fall below two or three ounces; from the gradual effects of advanced age, however, and independent of pregnancy, the uterus shrinks, becomes paler in color, and harder in texture. Finally at each successive recurrence of menstruation a complete removal of the superficial part of the mucous membrane takes place by a process, which we can describe but not explain. The removal is said to commence close to the cervix or at the os internum^ and to progress toward the fundus during the remaining days of the flow of blood. As the shape and topographical relations are sufficiently described in the standard Anatomies, we confine ourselves principally to the histology.

The descriptions are arranged in the following order :

  1. Muscularis.
  2. Mucosa corpus uteri.
  3. Mucosa cervicis.
  4. Blood-vessels.
  5. Lymphatics.

1. Muscular Coat

The volume of the muscularis varies greatly with the condition of the uterus, for during pregnancy the muscles undergo a progressive hyj)ertrophy, which is so great that not only is there an enonnous exj^ansion corresponding to the dilatation of the uterus, but also a great thickening of the coat. The increase in volume is due — 1, to the growth of the single fibres (in length from 44-68 At to 220-560 /i) ; 2, it is said also by the development of new muscle cells from small granular cells. After parturition the fibres in part return to their original size, in part undergo fatty degeneration (KoUiker, " Gewebelehre, 180T, p. 566).

The disposition of the fibres is most readily elucidated in uteri near the end of gestation. Having made no original observations on this subject, I transcribe the following passage from Quain's " Anatomy " : '* The external layer of the muscular coat forms a thin superficial sheet immediately beneath the peritoneum, and incomplete strata situated more deeply. A large sharo of these fibres, beginning as longitudinal bands at the cervix, arch transversely and obliquely over the fundus and adjoining jmrt of the body of the organ, and pass on each side into the broad ligament. Of these some at either side run toward the commencement of the round ligaments, along which they are in part prolonged to the groin ; others pass off to the Fallopian tubes, and strong transverse bands from the anterior and posterior surfaces are extended into the ovarian ligaments. Other fibres run hack, from the cervux uteri beneath the recto-uterine folds of the peritoneum. The inner layer of the muscular coat, which is also thin, is composed of fibres which are found chiefly on the back of the uterus, and stretch over the fundus and toward the sides, running somewhat irregularly between the ramifications of the bloodvessels." On the inner boundary the mucosa is quite sharply set off from the muscularis ; an erroneous contrary statement is frequent in English and American works.

It is commonlv asserted that the muscular coat of the uterus is largely made up of the hypertrophied muscularis mucosae. The evidence for this view is not to be found either in the anatomy or in the developmental history of the uterus, but, so far as I can ascertain, solely in the preci)ncej)tion that every mucosa must have a special muscularis to itself, as is the case in the intestine, for example. Comparative anatomy, however, is conclusive on this point; for it is not rare to find a mucosa without the special muscle layer. The true morphological relations are probably the reverse of those which have been assumed by the view hei"o criticised ; the primitive form is probably a mucosfi composed of epithelium and sub-epithelial connective tissue resting on a muscnilar layer, as in the uterus ; the secondary form, that in which other muscular fibres have been differentiated to form a special layer, the muscularis mucosae.

The muscle fibres have been shown by Elischer, 76.1, to differ somewhat from the fonns known in other organs. They are elongated cells, often spindle-shaped, but frequently broad and stumpy ; in the pregnant uterus they are enlarged and flattened ; in length they increase from 40-00 i± (virgin uterus) to 300-600 m (uterus at term) ; in transverse section they are seen to be more or less distinctly polyhedral ; their ends and sometimes their sides bear branching processes; they have one, sometimes two, or even more nuclei, which are usually oval, sometimes round, and usually nucleolated; the nucleolus ia eccentric. The nucleus is surrounded by granular matter, which stretches out toward each end of the cell; often the granules are separated by a clear space from the nucleus. This space has been obsen'ed by various authors. Eimer has found it in several sorts of cells and gives it the name of hyaloid. It is a peculiarity of the uterus that its muscle cells vary greatly among themselves in appearance.

2. Mucosa Corporis Uteri

A. Virginalis

At birth the mucosa of the body of the uterus is about 0,2 mm, thick, soft, pale gray or reddish-gray ; it consists of a covering ciliated cylinder epithelium and a connective-tissue layer; it is without glands, the glands not appearing usually until the third or fourth year, and developing very slowly up to the age of puberty. Wyder, 78, 1, has shown that the time of the appearance of the glands is eztramdy variable.

In the virgin resting uterus after puberty the mucosa is about 1 mm. in thickness. It is sharply marked off from the muscularis. The glands are tubular, often bifurcated in their lower third, round or oval in transverse section; Uiey run more or less perpendicularly to the surface of the membrane, upon which tliey open; yet, strictly speaking, this is true of the glands in their upper half only, and even in that part their course is not straight but wavy. In their lower half they deviate much more, being more insular and i tortuons, the fundus curved sometimes even so much as to run parallel to the muscular layer (G. J. Engelmann, 75. 1) . These differences between the upper and lower parts of the glands arc accentuated during menstruation and gravidity. The glands are invaginations of the uterine epithelium, are accordingly lined by ciliated cylinder cells, and have a nucleated basement membrane (Fig. 1, d), formed by a layer of anastomosing connective-tissue cells (Leopold, 74.1), Overlach, 8fi. 1, however, expressly denies the existence of any such membrane in the human uterus examined by him. The glands reach to, and may even slightly penetrate, the muscularis.

Fig. 1. Connective tissue of mucosa, uterus of pig

Fig. 1. Connective tissue of mucosa, uterus of pig

Between the glands is found a somewhat embryonic connective tissue, consisting of elongated cells with oval nuclei and branching processes, which anastomose with one another * (Fig. 1) ; the spaces of the cellular network communicate, according to Leopold, Ls.c.j with the lymphatic vessels of the muscularis and external serosa, and may therefore be i-egarded as lymph roots or lymph spaces. The branching spindle-cells resemble somewhat those formed in the umbilical and other embryonic structures, and known under the name of mucous tissue. They tend to crowd together around the bloodvessels and glands. There do not appear to be any fibres in this layer, although some observers have so stated.

Between the spindle-cells are small, round cells, probably wandering cells (leucocytes), which vary greatly in number.

The blood-vessels enter as veins and arteries from the muscularis, and take a winding course toward the surface ; the capillaries form a network around the glands and under the surface of the mucosa.

B. Decidua Menstrualis

The function of menstruation involves great changes in the mucosa of the bcxly of the uterus. We distinguish three periods: 1, tumefaction of the mucosa, with accompanying structural changes, taking 5 days, or, according to Heusen, 10 days; 2, menstruation proper, about 4 days; 3, restoration of the i*esting mucosa, about 7 days. The times given are approximative only. The whole cycle of changes covers about 16 days; as the monthly period is about four weeks, the i)eriod of rest as thus calculated is only al)out 12 days.

1. Tumefaction

A few days before the menstrual flow the mucosa gradually thickens; the surface becomes irregular; the openings of the glands lie in depressions. The connective-tissue cells are increased in number, and it is said by some authors in size, but the increase in size I doubt; the number of round cells increases; the glands expand and become more irregular in their course; a short time before hemorrhage begins, the blood-vessels, especially the capillaries and veins, l)ecome greatly distended. We must assume that the connective-tissue cells proliferate, but we have no satisfactory observations upon their division. It was formerly asserted that the mensti-ual decidua contains decidual cells, but in all the specimens I have studied there are none present.

2. Menstruation

When the changes just described are completed, the decidua menstrualis is fully formed, and its partial disintegration begins. The process commences with an infiltration of blood into the subepithelial tissues: this infiltration has hitherto been commonly explained as due to the rupture of the capillaries ; but as no ruptures at tliis period have been observed, Overlach, 85.1, very justly regards this explanation as inadmissible and thinks the infiltration occurs last (Jiapedesin. It lasts for a day or two, and is apparently the immediate cause of a very rapid molecular disintegration of the superficial layers of the mucosa, which in conseciuenco are lost; the sui)erficial ])lood- vessels are now exposed, and by rupturing cause the W(»ll-known hemorrhagia of menstruation ; by the disappearance of its ui)imt iM)rlion the mucosa is left without any lining epithelium, and very much (and abruptly) reduced in thickness. Its surface is formed by connective tissue and exposed blood -vessels. The third stage ia the restoration of loet parts. Signs of fatty degeneration are found during the above-mentioned dieintegration. Kundrat and Engelmann, 73.1, supposed this degeneration to precede and cause the hemorrhage; but thia view has not been confirmed by subsequent investigation, it having been found that the degeneration begins later than the bleeding. Overlach, 86.1, suggests that the hemorrhage is caused by the gorging of the veins and capillaries, which in its turn is caused by the contraction of the muscles of the uterus compressing the thin-walled veins. Against this view I would urge that it is not shown that marked contraction of the muscles precedes the bloody discharge, and that if it does occur it cannot be assumed that it would cause sufBcient compression of the veins to produce capillary ruptures.

•Company also Sfhinldt, Ainer. Journal Olwt<?t,, Jan., 1HS4.

It is desirable to add a few words as to Williams' view, 76.1, 76. 2. This author has maintained that the whole, or nearly the whole, of the mucosa disappears from the body of the uterus during menstruation. This opinion is often cited as authoritative, espe-i cially by English and American writers, but it is now definitely/ known to be erron^itB (Leopold, 77.1, Underbill, 75.1, ct al.).l It was based upon — 1, failure to consider the effects of disease upon the uteri observed {cf. Wyder, 78.1, 24); 9, erroneous observations; 3, erroneous interpretations, involving a total disregard of the elementary laws of histogenesis.

Minot1897 002.jpg

Fig. 2. Vertical section of the mucosa carpus uteri of the first day of menstruation

Minot1897 003.jpg

Fig. 3. Mucous membrane of a virgin uterus during the first day of menstruation

Minot, 98, 413-4 Hi, describes and figures a normal vii^n uterus near the close of menstruation. " Tlie mucous membrane is from 1.1-1.3 mm. thick; its surface is irregularly tumefied; the gland openings lie for the most part in the depressions. In the cavity of the uterus there was a small blood-clot. The mucosa is sharply limited against the muscularis, Fig. 3. In transverse sections one sees that the upper fourth of the mucosa is very much broken down and disintegrated, Fig. 3, dj the cells stain less than those of the deep portions of the membrane; as represented in the figure the tissue is divided into numerous more or less separate small masses; some of the blood-vessels api)ear torn through, but it is diflBcult to make sure observation." Overlach, 85.1, considers it probable that the infiltration of blood takes place by diapedesin, not by rupture of the capillaries. The superficial epithelium, cp, is loosened everywhere ; in places fragments of it have fallen off, and in some parts it is gone altogether; it stains reiidily with cochineal and its nuclei color well, the epithelium diflfering in this respect from the underlying connective tissue, which does not stain well; the blood-vessels in the disintegrated layer are for the most part small. The deeper layer of the mucosa is dense with crowded, well-stiiined cells, which lie in groups separated by clearer lines ; in the figure this grouping shows less plainly than in the preparation ; the lighter channels arc perhaps IjTiiph vessels — a suggestion which occurs to me because in so-called '* moulds" one sometimes finds similar channels crowded with leucocytes. The cells apj)ear to be the proliferated interglandular tissue ; there are very few leuc(X?ytes, so far as I can distinguish ; the cells have small, oval or elongated, darkly stained nuclei, with a very small granular protojJasmatic body each; there is certainly no noticeable enlargement of the cells, but only a remarkable multiplication.

3. Restoration of the Mucosa

At the close of menstruation the mucosa is 2-3 nmi. thick; the regeneration of the lost layers begins promptly *md is completed in a variable time, probably five to ten days. The hypenemia rapidly disappears; the extravasated blood corpus(*les are partly resorbed, partly cast off; the spindle-cell network grows upward, while from the cylinder epithelium of the glands young cells gn)w up and produce a new epithelial covering; new subepithelial capillaries api)ear. The details of these changes are imi)erfectly known ; they effect the return of the mucosa to its resting-stage.

C. The decidua graviditatis

The decidua graviditatis is the decidua menstrualis preserved in nifii^ and considerably metamorphosed in consequence of pregnancy. The prest»rvation is initiattKl by the presence of a fertilized ovum in the upjx^r end of the Fallopian tuln?, as is shown for various manunals by ol>servation, and for man by conclusive inference; and the preservation is deiK»ndent for its continuance upon the further development of the ovum in vtero. In the very youngest gravidity yet studied (twelve days) very great alterations have occurred, and we are reduced to hypotheses to ex))lain how these alternations are effectcnl. The ovum at this staj^^o is already attached to the wall of the uterus, and is comi)letely enclosed by a si>ecial covering known iis the decidual reflexa. The arrangement of the parts can also be followed in older ova, and is illustrated by the accompanying "vvocKlcut, Fig. 4, which n^presents a median section of a uterus about five we(»ks pn^gnant. The whole uterus is considerably enlarged; the nnicosa lining the uterus is very greatly thickened ; to one part of it the ovum is attachcnl; the mucosa also rises all aroimd the ovum, completely covering it in, so as to make a closed bag. The ovum itself is a sjick, known as the chorionic vesicle, which is covered on all jwirts by shaggy villi, and encloses the small embryo in ita interior; it is very important to iioto tliat only the tips of the chorionic villi come in contact with the mucosa. The mucosa, we thus leam, is divided into three parts : X, the decidua serotina, the area of the uterine wall, a s, to which the ovum is attached; 2, the decidua I'era, comprising till the remaining portions of the mucosa fonning part of the walls of the body of the uterus; 3, the decidua refle.rt(, the arching dome of maternal tissue, r r, which rises trom the walls of the uterus and completely encapsules the ovum.

If the wtUls of the uterus are cut through and simply reflected, leaving the reflex intact, the appesirances will be found essentially as in Fig, 5. The mucosa is enormously hypertrophied, and contains a great many dilated, irregular blood sinuses. From one part hangs down a lai^ bag, the decidua rejtexa, D. re/., nearly filling the cavity of the utenis. The reftexa presents the same general appearance as the surface of the uterus; if the ri'Jfexa \x> opened we come upon the villous chorion of the oi^um, and find as previously stated that only the tips of the villi are united with the surface of the rejtexa or serotina.

To form the placenta the serotina and the parts of the villi and chorion connected witli it (chorion frondosum of later stages) undergo synchronous hypertrophy and metamorphoses and and become closely united, compare Chapter XVII. In gross appearance the decidua is reddish-gray, spongj- or pulpy, soft and very moist; after the fourth month it acquires, especially in the superficial layers, a duller brownish color, which subsequently becomes more marked ; this coloration is due to the decidual cells. The vera and serotina are divided each into an upper or superficial more compact layer, and a deeper cavernous or spongy layer, Fig. (j; the two layers are usually of about equal thickness, but the cavernous layer sometimes encroaches upon the compact layer. After the fifth month, they are found very distinctly differentiated. The lumina of the deep layer are the cavities of the enlai^ed and irregular uterine glande. During the first two or three mouthe the scattered openings of the uterine glands can »till be distinguished over the surface alike of the vera and serotina and over both surfaces of the reflexa. The surfaces of the vera and reflexa, tlioi^h somewhat irregular, remain more or less smooth ; the inner surface of the refiexa is more irregular, and the protuberant parts are united with the tips of the foetal chorionic villi.

Minot1897 004.jpg

Fig. 4. Semi-diagrammatic outline of the anteroom-posterior section of the gravid uterus and ovum of five weeks.

Minot1897 005.jpg

Fig. 5. Uterus about forty days advanced in pregnancy. after Conte. The uterus has been opened by cutting through the anterior wall and reflecting the sides.

The surface of the decidua serotina becomes very irregular during the progress of pregnancy. Rohr, 88. 1, hais distinguished three kinds of projections in a uterus of the eighth month, viz. : 1, Hillocks, 1-4 mm. high, and with broad bases, their summits pointed, irregular or even branching; 2, columns, beginning with a slightly expanded base, narrow stalk and often enlarged ends ; the columns are long and stretch up toward the chorion, which they actually reach at least in the peripheral parts of the placenta; in the central region they rise more or less vertically, but obliquely in the peripheral region; in sections of the placenta they are often cut across, and give rise then to the appearance of islands of decidual tissue in the midst of the villi ; 3, septa, with wide bases rising irregularly to the height of 0.5 to 1.5 cm. ; it is by these septa that the placenta is divided into the so-called cotyledons, compare Chapter XVII.

The origin of the decidua reflexa is uncertain, there being no actual observations upon its genesis. The only view which has hitherto commanded attention is the following : When the ovum attaches itself to the wall of the uterus, the mucosa (decidua) is supposed to form an annular upgrowth around it ; the upgrowth continues making first a high wall, then arching over, and finally closing at the top, dome-like. I do not know with whom this hypothesis originated.

In certain rodents also there is a decidua reflexa. Selenka has shown that in them the ovum becomes completely buried in the uterine mucosa, and that the part of the mucosa covering in the ovum is converted into the reflexa as the ovum expands. In the hedgehog a reflexa is formed, according to Hubrecht, in a similar manner.

Disappearance of the Decidua Reflexa. — A very important change in the disposition of the parts takes place usually during the fifth month, viz. : the reflexa^ which, by its own expansion, corresponding to the growth of the ovum it encloses, is pressed close against the vera, disappears. Its disappearance has long been known, but until recently was unexplained; it seems safe now to say that it degenerates and is resorbed, compare p. 19. In consequence of the disappearance of the reflexa the outermost layer (chorion Icei^e) of the ovum comes into direct contact with the decidua vera. Before the fifth month, if we cut through the uterine wall in the region of the vera, we come upon the decidua reflexa ; after the fifth month a simiUxr cut brings us upon the chorion of the foetus.

The glands are alreiuly dilated in the menstrual mucosa; in pregnancy the dilatation is continued, Init is still chiefly confined to the deeper {wirts of the glands. In the same proportion as the uterus expands the deep portions of the glands become stretched in their transverse diameter and appear during the latter half of pregnancy in sections of the decidua, Fig. 10, as narrow fissures; by the fifth month the glands can no longer te traced in the upper compact layer, their ducts being obliterated. The partitions left between the glands are quite thin, Fig. 10; they carry the blood-vessels and contain spindle cells, and, it is said, also multinucleate giant-cells after the fourth month. Compare the description ]x?low of the serotina of the eighth month. The spindle cells, as stated by Langhaus, resemble smooth muscle cells in appearance, but when isolated are seen rather to be broad, round, and flat; they ought probably to be regarded rather as true decidual cells than as merely enlarged connective-tissue cells.

The epithelimn of the glands very early breaks down, as described by Minot, compare below, p. IG. The epithelial cells at first lie scattered singly in the gland cavity, although patches of them still adhere to the walls; the cells disintegrate. I have observed this degeneration in every one of a large number of specimens which I have examined of all ages up to seven months. The deg^ree of breaking down may be said in a general way to advance with the duration of pregnancy, but even at term patches of intact epithelium and groups of single ceUs are always recognizable. The openings of the glands have oeen shown by Mogilowa, 91.1, to be closed by the growth of decidua; this fact is important, for it shows that the glands cannot discharge any secretion, and shows further that we must discard the suggestion made by Minot, 98, 420, that some of the persistent openings on the surface of the placental decidua are glandular and not vascular.

The blood-vessels of the mucosa ai-e all enlarged, those in the deeper parts to a lesser degree than the superficial capillaries and veins, which are enormously dilated, forming huge, sinus-like cavities in the upper stratum of the decidua. During the latter part of pregnancy the vessels are less conspicuous. The remarkable arrangement of the blood-vessels in the decidua serotina is fully described in Chapter XVII. ; it will suffice, therefore, to state now merely that the arteries and veins both open upon the surface of the decidua, so that the maternal blood circulates in the spaces between the villi of the placental chorion.

The following changes in the blood-vessels must be noted, beside those alread}' mentioned in describing the gross appearances. The vessels of the vera and reflexa reach their maximum development at the end of the second month, when they begin to atrophy, preparatory to finally disappearing. Apparently in the serotina, also, the blood-vessels are reduced in volume and number toward the end of pregnancy ; but this alteration needs ver\' much to be further investigated.

Growth of the Decidua

With the growth of the foetus and the consecjuent dilatation of the uterus, the deciduse, of course, must increase rapidly in superficial extension. In fact there goes on a steady growth of the tissues, which however is not suflScient to effect the expansion of the membrane throughout the whole period of pregnancy in both superficies and thickness. The growth begins by a thickening of the mucosa within the area of the uterine wall to which the ovum is attached, so that during the third and perhaps fourth week this area (serotina) is the thickest portion of the decidua (Kollmann, 79.1); but the vera and reflexa also thicken, the former much the most, and soon outdo the serotina. By the end of the fifth week the refiexa measiu^s nearly 2 mm. and the vera fully 1 cm. The absolute thickness of the serotina does not change much after this period, remaining 3 mm. or a little less up to the end of pregnancy. On the other hand, by the eighth month the reflexa has entirely disappeared, and the vera is reduced to about 2 mm. It must be added — 1, that the reflexa is thinner over the poles opposite the serotina than elsewhere, and 2, that the vera thins out toward the cervix and toward the opening of each Fallopian tube.

The decidual cells are the most striking of the histological elements of the decidua. They are i^ery large ^ somewhat flattened, roimded, oval, or branching cells, which assume a characteristic brownish color after the fourth month ; they usually have a single, often nucleolated nucleus, but sometimes two, three, or more up to thirty or forty. Fig. 1 1 . They are exceedingly numerous and continue increasing in number up to nearly if not quite the termination of gestation. In size they vary from 0.03-0.1 mm. Kundrat and Engelmann, 73. 1, and others maintain that the cells undergo fatty^ degeneration before delivery, and attribute the loosening of the placenta to the very fact of the fatty metamorphosis. This view is at best questionable, and it is even doubtful whether the fatty change is a constant phenomenon. Of the decidual cells, we notice particularly the very large ones (giant cells of Leopold), with numerous nuclei and often with branching processes ; the number of nuclei varies from ten to thirty and more. These giant cells are said by Leopold, 77. 1, to appear quite abruptly and abundantly during the fifth month. They lie at first principally in the neighborhood of the blood-vessels of the deep parts of the decidua; they do not occur in the reflexa, and are far less numerous in the vera than in the serotina. The multinucleate decidual cells are perhaps only intermediate stages in the multiplication of the uninuclear cells, each nucleus of the large cells finally separating from the parent with its share of the parent protoplasm to make a new decidual cell; if this is the case it accounts for the final disappearance of the giant cells. As regards tlie function of the multinucleate cells we know nothing; in the rabbit, however, the multinucleate decidual cells have a glycogenic function (see Chapter XVII.), but they differ very much in microscopic appearance from the human multinucleate cells, and perhaps differ equally in function.

The decidual cells are most abundantly crowded together in the upper or compact layer, and contribute much to give that layer its main characteristics. B}" the eighth month they are found to have wandered into the cellular hiyer of the placental chorion, as is more fully described in the chapter on the chorion, apparently finding an entrance at the edge of the placenta.

Scattered among the decidual cells may be found a number of smaller cells which are more conspicuous during the earlier months, and are usually regarded as wandering cells (leucocytes). Langhaus, 77. 1, 110, regards the leucoc}i;es as the parents of the decidual cells — a view I cannot accept.

The origin of the decidual cells was long uncertain. Three views contended for acceptance: Ist, they are modified leucoc>i:es (Hennig, Langhaus just cited above, Sinety, 76.1,); 2d, they arise from the connective- tissue cells of the mucosa (Hegar und Maier, Leop<:)ld) ; 3d, tbev are ]m)duced by the epithelium. In favor of the first view there has never been, to my knowledge, any evidence of importance. The sec*ond view has been definitely established by Minot, 98, 429.

The epithelial origin was first advocated by Frommel {Aerztliches Intelligenzblatty Munchen, 1883, No. 21) for the mouse; by Overlach, 85.1, for man. Overlach traced the decidual cells to their origin in the epithelium, but his observations are restricted iosL single uterus with pseudo-menstruation from acute phosphorus-poisoning. In the epithelimn of the cervix of the uterus in question the following developmental stages of the decidual cells were foimd: 1, cells with a mother nucleus and one or several, up to fifteen smaller daughter nuclei; 2, cells with a little clearer though granular protoplasm collected around the daughter nucleus (or nuclei) ; 3, cells in which the protoplasm about the daughter nuclei has increased and is separated by a clear vacuole-like space from the protoplasm of the parent ; we have then a mother cell, much distended, with a vacuole partly filled by a daughter cell, or by several such huddled together; 4, young decidual cells, lying just under the epithelium and closely similar to the endogenous brood in the cells. The observations of A. Walker, 87. 1, on a case of abdominal pregnancy maybe taken as confirming Overlach. Walker found that the peritoneal epithelium at certain points in contact with the chorion had proliferated, forming several layers of cells, presenting an obvious similarity to true decidual cells. Isolated cells of a similar character were observed in the underlyingconnective tissue of the peritoneum. It thus apj^ars that the ovum may cause in other epithelia than the uterine a cell growth analogou*) to that described by Overlach. Walker, it must be added, maintains that in his specimen the pseudo-decidual cells also arise in part by metamorphosis of the connective-tissue cells. I am inclined to interpret Overlach and Walker's observ^ations as evidence of hyperplastic degeneration, and not of the production of decidual cells.

The manner in which the true decidual cells arise is described in the next section. For a description of the fully developed cells see p. 18.

Uterus One Month Pregnant

The specimen to be described came from a woman who conunitted suicide by violence. The specimen was received in very fresh condition, but the reflexa was badly torn ; the embryo had been removed, and I was therefore unable to verify the age, or investigate the attachment of the villi of the chorion to the uterus. There was a beautiful corpus luteum in one ovary, quite similar to that figured by Dalton in his report on the corpus uteum in the Transactions of the American Gynaecological Society for 1877, Fig. 9. *

My specimen enables me to confirm in most respects Turner's accurate description of two uteri of about the same age, 79.1, 546-548. The inner surface shows the hillocks (Inseln) described by Reichert in the uterus of two weeks studied by him, which have been figured by Coste in slightly older specimens, and found by Turner also, 79.1, 540.

The four illustrations given herewith are all from sections through what I suppose to be the placental region.

There is an upper compact layer. Fig. 0, 2), and a lower cavernous layer D' ; the caverns being gland cavities, which appear as rounded areolae parth line<l witli epithelium partlv filled with broken-down epithelial cells The drawing reproduced m Fig ( was obtained by drawing the outlines -len carefully stippling the areas occupied by the connective tissue, representing the blood-vessels by double out— -nl' 1^"®8, and omit^ ting the glandular epithelium altogether. It will bo noticed that about three - fourths of the diameter of the mucosa is oc^ cupiodbytbe<^vvj emoua layer, IJ. ^— ,ai+ The upper or compact layer is shown in Fig. 7. The surface is w ithout any trace L f epithelium, and IS covered only by a thm fibrous and granular coagulum coagf ; the ti-«ue itself con-gl' sists almost exclusively of young decidual cells, a, d, with a clear, homogeneous matrix; here and there are leucocytes, but they are iii us nowhere numer

compact lnjpr f ui<l n lower cavHrDUua layer £ gt gl glands are Cells are all quite spiral artery ,

bodies deeph stained by the eosin the nuclei are round, oval, or slightlv irregular in shape o wrselj granular and sharp in outline; the cells themselves, though irregular and variable m shape, are all more or less rounded with iiroct-MSt's running off in various directions; scattereil betwetiu the cells tire many sections of their processes; occasionally it can bo seen that two cells are connected; in fact, we have in this tissue evidently a modified embryonic or so-called anastomosing connective tissue. Now, as wo know through the obser\'ati<ins of Leopold, 77.1, wliich I have verified, the connective tissue of the uterine mucosa, consists of anastanosing cells, and as stated in the previous stwrtion the <m'11s are foimd proliferating in the menstruating uterus; we have, therefore, only to imagine the cells

layer The gland ducts are completely devoid

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Fig. 6. Uterus one month pregnant ; outlines of the glands from a vertical section

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Fig. 7. Uterus one mouth pregnant ; portion of the compact layer of the decidua seen in vertical section

enlarged with certain accompanying modifications to obtain the tissue figure in Fig. 7. There ia no special formation of cells aroimd the blood -vessels, where, according to Ereolani, the decidual tissue arises by new formation. In Turner's specimens the upper part of the compact layer was imperfectly preserved, but according to Lis description there appears to have been a coagulum similar to that which I have found, but thicker. In the deep part of the layer the cells are lees enlarged, and when the cavernous layer ia reached there occurs a rapid transition in the character of the cells, which become smaller and more fusiform, and their nuclei more elongate, smaller, and deeper stained by alum -cochineal. The gland openings upon the surface of the uterus lead into tubes. Fig. C, gl', which run shghtly obliquely through the compact layer, taking a more or less nearly straight course and joining the contorted gland tubes, Fig. t>,

gl', of the cavern

of lining epithelium, which has diKippeared except for a verjloose cell, occasionally found lying free in the ducts; the cells have not fallen out from the sections, but were lost before the tissue was imbe<ided.* The ducts then are wide tubes running nearly strai ght through the upper part of the decidua and bounded directly by the decidual tissue; they communcate below with the contorted cavities.

The cavernous layers contain numerous spaces, the areolsB of Turner, 79.1, 547, who was uncertain as to their character, though he ascertained that many of them belong to the glandular system. In my specimen it is perfectly clear that all the larger areolae belong to the glands, which must be extremely distorted and distended to give the shapes shown in Fig. (I. The thin dissepiments between the areolee are composed of connective tissne, the long dark nuclei of which. Fig 8, are strikingly different from those of the cells of the compact lajer, Fig 7 The areolse present two extreme modifications and all intermediate phases between these two The smaJler areolee are lined by a well-preserved cjlinder epithelium, or by one w 1 in which the cells are separat" ed by small fissures; in other areolse the cells are a little larger. Fig. 8, each for the mcst part cleft from its fellows and some of them loosined from the wall and lying free in the caWty. The other extreme is represented in Fig. 0, the size of the areohe is much increased — compare Figs 8 and 9— both drawn on ot the same scale ; the epithelium '™ is eiltirely loosened from tlie w all, and the cells lie separately in the cavity which they fill ; the cells are greatly enlarged, their bodies having tbi-ee or four times the diameter of the cells in the small are<iUt ; they have not the cj'Hiider shape, but are irregular in outline ; their protoplasm is finely granular and stains rather lightly ; the nuclei are large, rounded, granular, and with sharp ouuines; they are less darkly stained than the nuclei of the epithelium of Fig. S. The obvious interpretation of the appearances described is that the glandular epithelium is breaking down, being lost altogether from the ducts, but is still i>rest*nt in the deep portions of the glands ; in breaking down the cells separate from one another, and tlien from the wall, and falling into the gland cavity fliere enlarge, the cavity enlarging also. Similar appearances are also found in " moulds" of the second month; very likely they have been oft«n observed and mistaken for pathological changes.

Fig. 9. Cteruaone

The blood-vessels of course lie in the dissepiments between the glands. I observed nothing to correspond with the " colossal capillaries dilated into small sinuses," mentioned by Turner, 79.1, 648. Were not these supposed capillaries gland cavities, from which the epithelium had fallen out? Occiisionally the sections pass through a spiral arterj', Fig. C, art, which is cut again and again as it twists around in its characteristic separate column of connective tissue.

Decidua Serotina at Seven Months

In anormal uterus about eight months pregnant I find the following relations : The serotina is about 1.5 mm. thick, and contains an enormous number of decidual cells. Fig. 10; the cavernous, D', and compact layers, D", are very clearly separated ; the mucosa is sharj'ly marked off from the muscularis, although scattered decidual ceiis have penetrated between the muscular fibres. The muscularis is about 10 mm. thick and is characterized by the presence of quite large and numerous venous thrombi, especially in the ]tart toward the decidua. The decidua itself contains few t>Inod-ies.te1'i. Upon the surface of the decidua can be distinguished a special layer of denser decidual tissue, which in many places is interrupted by the ends of the chorionic villi which have penetrated it, aa is well ehown in tho accompanying Figure 10. The^and cavities of the spongy layer, D', are long and slit-like; they are filled for the most part with fine granular matter, whidi stains light blue with hfematoxylin ; they also contain a little blood, and sometimes a few decidual cells. I have also seen in them a few oval bodies several times larger than any of the decidual cells, and presenting a vacuolated appearance. What these bodies are I have not ascertained; in a number of uteri over two months pregnant I have found them invariably present. In many places tho glandular epithelium is perfectly distinct ; its cells vary greatly in appearance, neighbors being often quite dissimilar; nearly all are cuboidal, but some are flattened out; of the former a numter are small with darkly stained nuclei, hut the majority of the cells are enlarged, with greatly enlarged hyaline, very refringent nuclei. There are also in many of the gland spaces isolated enlarged cells, which have detached themselves from the wall, and in some cases the detached cells nearly fill the gland cavity, very much as in Fig. 9.

The decidual cells of the cavernous layer, Fig. 10, D, are smaller and more crowded than most of those of the compact layer. The largest cells are scattered through the compact layer, but are most numerous toward the surface. They extend around the mai^n of the placenta and h&ve penetrated the chorion, in the cellular layer of which they are very ntmaerous (compare on this point the chapter on the Chorion) ; the immigration has im Eirted to the chorionic yer in question somewhat the appearance of a decidual membrane. Misled by this peculiarity, KoUiker and others have held this layer to be maternal in origin, and accordingly have described it as a "decidua subchorialiB. The error was, so far as I am aware, first definitely corrected by Langhaus, 77.1. The decidual cells exhibit great variety in their fentun^, Fig. 11. They are nearly all oval discs, so that their outlines varj' according as they are seen lying in the tissue turned one way or another; they vary greatly in size; the larger they are, the more nuclei they contain; the nuclei are usually more or less eJongated ; the contents of the cell granular. Some of the cells present another tj'pe, c ; these are more nearly round, are clear and transparent; the nucleus is round, stains lightly, and contaii» relatively few and small cliromatin granules; such cells are most numerous about the placental margin.

Fig. ll.—IAvitliuil 1x1 Is [rui FiK. 10: HAlnedwlth olur ' .. it anil/. TarloiM roroiB of cells, fi

Fate of the Decidua Reflexa. —The decidua reflexa is a distinct membrane up to the end, it is said, of the fifth month of gestation, and after that period it can no longer be found. Exactly at what time it disappears is not established by observation, though the fact of tlie disappearance has long been known, nor have we had hitherto any definite knowledge as to how it disappears, although its gradual attenuation and increasing transparency during the first four or five months have been familiar to us since the publication of Coste's magnificent atlas. The view most generallj^ accepted has been that it fused with the decidua vera, and that accordingly the layer of decidua nearest the chorion during the latter half of pregnancy represents the decidua reflexa.

I have had opportunity to study four well-preserved normal pregnant uteri of two, three, five to six, and seven months' gestation respectively. These show that at two months the decidua reflexa is imdergoing hyaline degeneration, that at three months the degeneration is considerably more advanced, and that by the sixth and seventh month the reflexa can no longer be found. These observations justify the theor}^ that the reflexa degenerates and is completely resorbed.

I will review briefly the actual observations :

First, the reflexa at two months. It starts from the edge of the placental area with considerable thickness, which is rapidly lost, most of the reflexa being a thin membrane and the thinnest point being opposite the placenta. The examination of sections shows that the entire reflexa is undergoing degeneration, which is found to be the more advanced the more remote the part examined is from the placenta. The chorion Iseve lies very near the reflexa, being separated only by chorionic villi, which are very much altered by degeneration, their ectoderm having become a hyaline tissue, which stains darkly, and their mesoderm showing clearly the partial loss of its cellular organization. In the region half-way between the base and the apex of the reflexa dome the tissue of the decidual membrane shows only vague traces of its original structure ; only here and there can a distinct cell with its nucleus be made out, for most of the cells have broken down and fused into irregular masses without recognizable organization. Ramifying through the fused detritus there are two layers of st)-called ** fibrin,"' or, in other words, of a hyaline substance, which like the " canalized fibrin" of the chorion stains very deeply with the ordinary histological dyes, carmine and logwood. The fibrin is much more developed upon the inner or chorionic than upon the outer side of the reflexa. It forms on the inner side a dense network, which on the one hand fuses with the degenerated ectoderm of the chorionic villi wherever the villi are in contact with the decidua; and on the other hand ramifies more than half-way through the decidua, the ramifications being easily followed, owing to the hyaline character and deep staining of the ** fibrin." Upon the outside the fibrin forms a thinner layer, and shows its network structure in many sections much less clearly. All of these points are illustrated by the accompanying figure.

In the uterus three months pregnant I find essentially the same conditions, except that the degeneration is farther advanced, since the traces of cellular structure in the reflcsa are still more vague and the fibrin is more develop*Kl. Tlie membrane is much thinner than at two montlis; the thickness is about two-thirds of what it was. Ill the fresli sixjcinien the membrane appeared much more transparent than before. In all the parts examined I found leucocytes present, and in the region of the reflexa near the placenta they are very numerous and conspicuous; it is natural to conclude that they are concerned iu the resorption of the degenerated tissue. In a section not far fi-om thu base of the reliexa the throe layers are distinct as at two montlis, there being a thicker inner an<l a thinner outer fibrin layer, while between them is a stratum in which remains of celts are seen ; occiisionally is an appearance which suggests a surviving decidual cell, and nearer the placenta the phantoms of cells become distinctly cells, and tnie decidual cells can be made out. The inner fibrin layer is much denser and its meshes smaller than in the two niDuths six-cimeo, the trabeculie of fibrin having become thicker during the month elapsed.

Those who cnuceive that there is a fusion l)etweeii the reflexa and verji, aro forced to seek for traces of the former membrane next the chorion, Thc\- may assume either that the epithelioid layer (chorionic ect(Hli'rni) is the remnant of the decidua, which forces them to leave the fate of the chorionic einthelium unexplained, or that the upper stratum of the decidua in the reflexa which is fused with and iictjuired the same structure as the imderlying vera. If my observations ou tho d<^neration of the reflexa are correct, and correspond, an there is sutBcieiit ground to believe they do, to normal conditions, then both assumptions as to the jiersistence of the reflexa involve the further and veiT impnjliable assiimption that the degenerated tissue is removed and replaced by fully oiganized cellular decidual tissue. It is obviouslj- more in accordance with our knowledge of degenerative changes to assume that the hyaline metamorphosis is necrotic and is succeeded by the disintegration and removal of the tissue. This accounts in a satisfactory manner for the absence of the decidua reflexa during the sixth and seventh month. The relations of the membranes at this period have been well described and figured by an admirable observer, Dr. G. Leoix)ld, whose views and one of whose drawings have been incorj)orated by Prof. O. Hertwig, in his '* Entwickelungsgeschichte" (third edition, pp. 210-217, fig. 147). Leopold holds that the epithelioid layer is the reflexa ; but what has just been said suffices, I think, to show that this view is untenable.

That the membrana decidua reflexa should degenerate and disappeiir no longer seems strange, since recent investigations have sliown that in many phicental mammals there occurs an extensive pseudopathological destruction of the mucosa uteri during gestation. These changes, which are best known in the rabbit (cf, ilinot, Biol. CeniralbL^ x., 114) vary considerably in character and are exceedingly remarkable both for their extent and for their numerous modifications, so that we need feel no surprise at the entire destruction of the decidua reflexa in man, nor at tlie form of the destruction being unlike the fonns hitherto found in other mammals.

As to the purpose or advcmtage of the sacrifices of maternal tissue we are in the dark. The same is true of the causation of the degeneration, although we must regard it as tlie result of a reflex Jiervous activity. It is becoming more and more evident tliat the nerves have a profound influence upon organization, and it is no strained hypothesis which places the structure of the mucosa uteri under the inunediate control of the nervous system.

The changes in the decidua at parturition require Bi>ecial description. During lalx^r a split occurs in the decidua serotina and vera; all the parts within the split — that is, toward the chorion — are expelled, their expulsion being part of the act of delivery ; the term devidna or caduca refers to the fact that the membranes are cast off; they are discharged after the fcetus, and, together with the vera and foetal envelojx)s, constitute the so-called after-birih. There are thus removt'd the superficial portions of the vera and serotina. The split, according to Friedlander, 70.1, 78.1, usually occurs in the upj)er or compact layer just al)r)ve the cavernous layer, leaving the surface of the utt»nis smooth and glistening, but the surface of the placental area is thrown into irregular hills and valleys. Sometinu'S the split i>ccui*s at or just Mow the upper limit of the cavernous layt.^r, in which case the surface of the uterus after parturition is jagged and iri*egidar. In rarer easels the split occui^ higher up in the Compact layer, leaving consequently by far the gi'eater part of the decidua hi situ quo (tnie. In all normal cases, however, more of the mucosa is lost than in menstruation, and a considerable iM>rtion is always left in utero; this latter portion contains the remnants of the uterine glands, and is the organ of regeneration for the entire mucosa; it has, of course, no e])ithelium \\\xyi\ its surface, which instead is formed by connective tissue and rui)ture<l blocnl-vessel (and l\Taj)hatics?). The layer of vera left on the uterus is usually about 1 mm. thick; that of the serotina may Ix? considerably less.

The post-partum regeneration of the mucosii begins very soon, but varies greatly in the rate with which it progresses, being very rapid in vigorous, healthy women and slow in weakly women. The retnon of the vera is restored more rapidly than the placental area.

The first step is the thickening of the mucosa to about 2 mm,, owiuK to the contraction of the uterus, which of course reduces the 6upei%cial extent without altering the volume of the mucosa. In conaeqtience of this change also the gland spaces become rounder and the course of the glanda straighter. I will bore interpolate a description of a human uterus, twelve hours after abortion, see Minot, 98, 42S. The uttrus whs aptwrently nonnal ; it was alrea*ly very much contracttnl; the mucosii measured about 1 mm. in thickness; the surface WiW ragj^l and more or less coverwl witli clotted LUmmI, presenting very much the apiJeanuice so superbly figured by Cost^" ("Devol. corps <ji^niBes," pi. x. Espwo hunmine). Vertical sections. Fig. i;t, show that tlie surfiicos of the mucosa are very uneven; on the free surface there is a thin layer of clotted blood, coagl; ' the upjM'r <)r comjMict layer of the ilecithm htw entirelj- disappeared, "leaving only the deep portion, T), permeated by numerous largo gland Bi)aces, between which are partitions containing the bro>viiish and hyaline decidual cells, and a great many blood corpuscles, which lie in the tissues as well as in the blood-vessels. The presence of blood corpuscles iu the tissues is jjrobably a constant feature of the decidua pout partum."

The second step is the restoration of the surface by the resorption of the blood and detritus, parallel with which advances the restoration of the glandular epithelium. These changes occupy apparently from seven to fourteen days. The cuboidal gland cella at this time appear swollen, with indistinct intercellular boundaries; the nuclei are alnioBt all enlarged until theynearly fill the cells; rapid cell division is going on. At this time also venous thrombi are very conspicuous, especially in the placental area, where they are found ireah and in various stages of progressing obliteration. Fig. 14. The thrombi persist for a long period (Leopold, 77.1, xii., 185).

The third step is the completion of the restoration of the glands up tti their external openings, and the regrowth of the normal connective tisBueofthe mucosa. The resulting stage was found by Leopold, 77.1, xii., 100, to hare been reached in a normal uterus three weeks after partiu-ition. Of this specimen lie gives the following description, which refers to the placental region, " As shown by the illustration (Fig. 14) the young mucosa is composed mainly of fine short Spindle cells, which form the interglandular tissue. They exhibit extraordinarj' proliferation, and are lowing themselves in numerous pnjcesses (Zapfen) intothemusculature, but still leaving the limits of muscularis and mucosa distinct as in every non-pregnant and pregnmit uterus. Secondly, between the young cells we find many bloodvessels, especially capillaries, in the neighborhood of which are collected blood corpuscles, haematin crystak, and pigment. Many appearances indicate the new formation of capillaries fr«m simple cir

Fig. H.— Section ot the placeoUl area of the iiteniK tliivK ivh^Iib poil ;Hirluui. J/nc, inuwwa: Mk. muKcularis After Leopolil.

of cells, which extend to the very surface. Thirdly, and most important, we find the young glands, which are short vertical follicles, imparting to the surface a more definite sieve-like appearance. Their cuboidal epithelium is spreading out from their mouths to recover the surface ; but at this time the new epithelium is not yet completed. The mucosa is still a wounded tissue; for its complete restoration there is still lacking . . . the vascular network." The fourth step is a double one: the restoration of 1, the superficial

epithelium, which is accomplished by the spreading of the growing epithelium from the mouths of the glands, and of 2, the subepithelial network of capillaries. The completion of this, the last step in the restoration, hiis been observed in a normal uterus six weeks after j)arturition.

A very different regenei-ative process is stated by DuvaJ, 90.3, to occur in rodents; he believes that in these animals the epitheUum is reproduced nearly simulUmeously over the rupture surface by a dii^ect transformation of the connective-tissue cells of the placental decidua.

4. Mucosa Cervicis Uteri

The mucosa of the cervix lias been only very imperfectly investigated. It resembles somewhat that of the body of the organ; but is distinguished ./i/'s^ by the possession of two kinds of glands, one agreeing with the utricular or uterine glands pro}x>r, the other of the "mulbeiTy" type, there being numerous alvc^olar bnmches of the gland cavity; second, by the character of its lining epithelium, com] )osed of enormous cvlinder cells of many shapes, in length averaging fully 55 /i {cf, Overlach, 86.1, 2U, 210flf.). The stratified epithelium of the vagina does not, it apj)ear8, normally extend inside the os. The utricular glands are lined by an epithelium like that of the corpus, while the epithelial cells of the '* mullK^rry glands resemble those lining the cervix; the latter glands are in fact strictly cervical, and apjjarently seci-ete only mucous matter; they are very likely important contributoi*s to the jJug of mucus which closes tlie cervix during pregnancy.

The cervix, except for this plug, remains oj)en during gestation ; it aLst) preserves its covering epithelium, and although it becomes tumefied during gnividity, and may, its claimetl by Overlach, participate in the formation of decidual cells, it never, as far as yet ascertained, fonns a true de(*iduous membrane.

A thorough investigation of the histology of the cervix in all pliases of the uterine functions would 1x3 extremely valuable.

4. Blood-Vessels

The uterus is supplied from four arteries: two, the ovarian, ninning along the broad ligaments and giving each a considerable branch to the fundus; two, the uterine, derived from the internal iliacs, rumiing to the cervix, and thence mounting by a very tortuous coui*se toward the fundus to there join the ovarian aileries. 1'he arteries give off very numerous Ijranches, which take a characteristic spiral course through the muscularis, and fonn frequent anastomose^s with one another. The arterial vessels of the uterus are further remarkable for the great development of their muscuhu* walls, all tlie more striking lx»causo the muscular coat of the capillaries and veins is slightly developed.

The capillaries are wider in calibre than usual, find form si>ecially distinct networks under the epithelium and aroimd the glands of the mucosii. The veins are very wide, almost sinus-like, even in the rcsting uterus.

During and just In^fore the m(»nstrual flow, and still more during the first hidf of pregnancy, the vessels are all dilated, and it is thought by some actually increased in number; this latter opinion may be fairly doubted. The incn»ase in the amount of blood is very obvious; indeed Rouget, 68.1, sjx^aks of the tissue of the uterus as erectile, but this adjective is not applicable in the anatomical sense, as KoUiker ha« very properly pointed out. The vascular enlargement affects principally the capillaries and veins (Turner). It is most marked during the second and third month of pregnancy; in the fourth or fifth month the vessels begin to atrophy, and by the eighth month, as previously stated, the vessels are far less immerous; these changes require further investigation. A uumlx3r of large venous sinuses remain, however, especially in the inner portion of the muscularis, and are highly characteristic of the latter half of the period of gestation.

Large thrombi normally appear in these sinuses, becoming first noticeable during the eighth month and j)ersisting several weeks post partum. Apparently they ct^ntinue to arise during the eighth and ninth months and even after delivery (Leoi)old). The thrombi, which were first discovered by Friedlilnder, 70.1, 76.1, and have been studied also by Leopold, are supposed by the latt-er author to be directly caused by an immigration of giant cells into the veins. LeojK>ld further supposes, 77.1, xi., 402-500, the presence of the thrombi Uj cause venous congestion of the uterus. Now, if it is true, as Brown-Sequard has maintained (** Experim. Researches Applied to Physiol, and Path.," 1850, 117, and BrownSe(|uard's Jouin. Phf/siol., i., lsr>s, 105), that carbonic acid excites toward the end of gestation uterine contractions very readily, tlien it is possible that the venous congestion above mentioned may be one of the proximate causes of parturition.

Additional facts in regard to the blood-vessels during pregnancy are given, pp. 23, 27.

6. Lymphatics. — Our knowledge of this subject rests principfdly ujxm the admirable memoir of Leopold, 74.1. The system begins in the intercellular spaces of the connective-tissue layer of the mucosa ; in this and in the muscular layer are lymph capillaries, which communicate with the subserous (subperitoneal) network of lymphatics.

" Special Physiology of the Uterus.— Our anatomical study has shown us that the most remarkable changes of the uterus during its menstrual and gestative functions are : 1 , the gradual thickening of the mucosa ; 2, the removal of the superficial portions of the mucosa, in the one case during the menstrual flow and in the other during labor; )^ the appearance of an enormous numlx>r of the very characteristic and jx>culiar de<*idual cells during the thickening of the mucosii. The menstrual and gravidital changes follow the same cycle, and differ from one another essentially only in two points: I, the time (x^cupied, and 2, the extent of the changes. In fact the alterations, though of the same character, are greater in extent and occupy a longer period during gestation than during menstruation. These considerations force us to the conclusion that the gravid uterus is j)assing through the menstrual cycle prolonged and intensified. The function of gestation is a direct modification of the function of menstruation, and the two are physiologically homologous. The deduction is s<^ evident that I have been surprised not to have yet encountered it clearly enunciated in any of the authors I have consulted.

That the decidual cells perform some very important fimction seems to me likewise evident from their great prominence, but until their history has been elucidated even as to details, we can hardly hope to ascertain what that function is. We may surmise that they are either organs of regeneration, or of nutrition for the embryo, or of both functions.

The cause of the formation of the decidua either in menstruation or in gestation is unknown. The presence of the impregnated ovum in the upper end of the Fallopian tube seems to be the cause of the arrest of the menstrual changes and the preservation of the decidua upon the uterine wall. How it produces this effect is unknown, but it is fair to assume that it takes place through the central nervous system. Experiment might demonstrate the nerv^ous pathways followed by the irritation and the reflex, and perhaps discover a trophic centre in the cord for the uterus. That the impregnated ovum, when it exerts this influence, lies in the upper end of the oviduct quite remote from the uterus seems certain from analog}^ \viih mammals. Presumably the ovum undergoes rapid degeneration during its passage through the oviduct, and can l>e saved only by fertilization at the start. Lowenthal, 86.1, who shares the too frequent misapprehensions of gjTifiBcologists in regard to the site of impregnation, and thinks in his philosophy that it is impossible for a remote ovmn to exert such a marked influence on the uterus, has advanced the hypothesis that the ovum is fertilized in the uterus and affects it by direct contact. His critic, Wyhoff {CenfralbLf. Gyiicek.y 1885, No. 20, 401), thinks impregnation may occur either at the ovary, in the Fallopian tube, or in the uterus ! Such references to opinions on this subject, advanced without proper knowledge, might be i-eadily multiplied.

But if the decidua graviditatis is product^d by the influence of the impregnated ovum on the menstrual membrane, we have still to ask. What causes the formation of the decidua moistrualis? To this no answer is possible. Pfliiger has advanced the theory, 66.1, that the ripening Graafian follicle exerts through the central nervous system a reflex action upon the uterus ; but, inasmuch as the attempt to establish a fixed relation in time between the ripening of the follicle and menstruation failed (Leopold, 83.1), it is imj)ossible to accept Pfliiger's theory at present. That menstruation is connected with ovulation appears probable, but that ovulation has a constant casual relation to the monthly period is by ncj means demonstrated. The belief in the connection is favored by the fact that the ojx^rative extirpation of both ovaries usually, hut not invariabh/, causes menstruation to cease. Putnam-Jacobi has advanced a theory in regard to the cause of menstruation (see Amer. Journ. Obst.y Apr., 1885), which is based upon singular false homologies l^^ween the ovary and uterus, and some physiological assumptions which are, I think, not admissible. Other theories, likewise not tenable in my judgment, have been advanced, but it seems undesirable io dwell upon speculative views.

The cause of the formation of the reflexa is connected with the ovum, since wherever the o^^lm is attached the reflexa is formed around it ; how the ovum after its attachment exerts its influence, is unknown. Since the position of the ovum determines that of the reflexa it becomes the more interesting to put the question, What determines the site of attachment of the ovum? which, unfortunately, is at present an unanswerable inquiry.

The cause of delivery is not ascertained, but has been much debated. Various suggestions have been made to explain why the decidua cleaves in two, and why the uterus contracts to expel the foetus. Our inquiry- as to the cause of birth may be resolved into two component questions : 1 , What is the stimulus which causes the uterus to expel the foetus ; 2, What causes the stimulus to act at a I'ertain peri oil after conception, I.e., what determines the duration of pregnancy? The second question I hope to discuss elsewhere.

As reganls the first question. What stimulus causes delivery? it is well known that various operative procedures can excite apparently by reflex action contractions of the pregnant uterus which will result in tlie expulsion of the ovmn. It is by taking advantage of this possibility that abortions (premature deliveries) are procured. Such stimulations as are referred to may be caused in the following ways: 1, by rupturing the iunnion and allowing the amniotic fluid to escape from the uterus ; 2, by the introduction of foreign bodies between the walls of the ovum and those of the uterus ; 3, by mechanical irritation of various parts, especially the cervix uteri, the external genitalia, or the breasts. With these facts in mind the hypothesis is imavoidable that the normal contractions of the uterus at full term are due to reflex stimulati(^n. Various authors have accepted this opinion and endeavored to ascertain the starting-i)oint of the stimulation. Mauriceau sought it in the uterus having reached the limit of its expansibility; Naegele in the irritation caused by the embryo, acting like a foreign Ixxly in the uterus; Engelmann, at least partly in the degeneration of the decidual cells; Harse and others, in the accumulation of carbonic acid in the blood of the uterus. None of these views are very well founded ; the two last deserve, however, a little more consideration. The fatty degeneration is not adequate, because in several instances it has been found wanting both before and immediately after birth (Sinety, 76.1, Meola, B4. 1). The carbonic-acid theory is presented in its most plausible form by Leopold, and has l^een already stated (p. 43) . To what is there said may be adde<l that it is not shown, 1, that venous thrombi cause the venous congestion of the uterus assiuneil by Leopold, and 2, that such congestion would charge the uterus ^vitli sufficient carbonic acid to excite contractions in it. Compare also Spiegelberg's Lehrbuch," 1880, p. 120.

We evidently have to do with a progressive maturation of the uterus — a series of changes wo cannot explain, but which is, as already pointed out, closely similar to the series of changes during menstruation. Hence it is probable that there is a common cause for the ending of the series (the casting off of the superficial part of the mucosa in both cases) ; in the delivery there is superadded the contraction of the uterus, and for this we must see a cause also. Therefore it seems tome that it is undesirable to search for one cause only for the whole process of birth.

The physiology of delivery does not fall within our scope ; for further information the reader is referred to Hensen's " Physiologie der Zeugung."

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Human Embryology: Introduction | The Uterus | General Outline of Human Development | The Genital Products | History of the Genoblasts and the Theory of Sex | The Germ-Layers | Segmentation | Primitive Streak | Mesoderm and the Coelom | Germ-Layers General Remarks | The Embryo | The Medullary Groove, Notochord and Neurenteric Canals | Coelom Divisions; Mesenchyma Origin | Blood, Blood-Vessels and Heart Origin | Urogenital System Origin | The Archenteron and the Gill Clefts | Germinal Area, the Embryo and its Appendages | The Foetal Appendages | Chorion | Amnion and Proamnion | The Yolk Sack, Allantois and Umbilical Cord | Placenta | The Foetus | Growth and External Development Embryo and Foetus | Mesenchymal Tissues | Skeleton and Limbs | Muscular System | Splanchnocoele and Diaphragm | Urogenital System | Transformations of the Heart and Blood-Vessels | The Epidermal System | Mouth Cavity and Face | The Nervous System | Sense Organs | Entodermal Canal | Figures | References | Embryology History

Cite this page: Hill, M.A. (2018, December 13) Embryology 1897 Human Embryology 1. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/1897_Human_Embryology_1

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