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Grosser O. VII. The development of the egg membranes and the placenta; menstruation in Keibel F. and Mall FP. Manual of Human Embryology I. (1910) J. B. Lippincott Company, Philadelphia.

VII. The Development of the Egg Membranes and the Placenta - Menstruation

File:Otto Grosser
Otto Grosser (1873 - 1951)

By Otto Grosser, Prague.

I. Introduction

The difficulties in the way of a comprehensive description of human placentation have been mentioned so often that a detailed re-enumeration of them is unnecessary here. The first stages, so necessary for the understanding of all the later ones, are lacking, just as they are in the case of the formation of the germinal layers, and, as in this case, must be conjectured by deduction and analogy. In the following description an endeavor will be made to state what has been determined with certainty, and, in connection with this, to call attention to disputed questions and to the probable significances of the phenomena described.

A statement of our knowledge in the field of comparative placentation may also be dispensed with, since it has repeatedly been given in detail within recent years.[1] The position which man occupies among the Mammalia on the basis of the structure of the placenta may, however, be indicated; and, in connection with this, the nomenclature employed in placental classification and the general morphological and histological processes involved in the formation of the placenta may be described.

Placentation is (in mammals) the intimate union (apposition or fusion) of the mucous membrane of the uterus with the outer layer of the ovum, the chorion, which becomes vascularized from the allantois[2] for the purpose of providing for the respiration and nutrition of the embryo and for carrying away its waste products.

Since the union of the chorion and the uterine mucous membrane is either an apposition or a fusion, the expulsion of the chorion sack after birth either may take place without injury to the uterine mucous membrane or a portion of the latter, the decidual membrane (membrane decidua)[3] may be expelled with it; hence the old division of the Mammalia into the lower Adeciduata and the higher Deciduata. But tissue destruction frequently takes place during pregnancy in the former, and, on the other hand, in many highly organized forms the placenta contains no considerable quantity of maternal tissue, if the maternal blood be disregarded, so that in these it is hardly proper to speak of decidua (Strahl). accordingly, Strahl [4] has employed the relations of the maternal blood as a basis of classification and has designated these placentae "in which post partum the spaces of the placenta which carry maternal blood are separated and expelled" complete placentce or placentce verce; while those simpler placentae, in which during and after birth the maternal blood-spaces remain intact, are termed half placentce or semiplacentce. The classification proposed by Robinson (1904) is practically the same, since his "apposed placentae" include those in which there is merely an apposition of the chorion to the uterine mucous membrane, while those in which there is fusion of the two he terms "conjoined placentae." In the same way the two groups proposed by Assheton (1906), that of the placentce plicatce with simple, non-proliferating chorionic epithelium, and that of the placentce cumulated with a greatly proliferated and thickened chorionic epithelium, traversed by lacunae for the maternal blood, agree essentially with the two divisions of Strahl.

The idea of placental types which the author[5] has conceived takes its origin from another standpoint. The nutritive material which passes from the maternal blood into that of the fetus in the lowest types of placentae passes in suCoession through maternal endothelium, connective tissue, uterine epithelium, portions of the uterine cavity, the chorionic epithelium, chorionic connective tissue, and the endothelium of the chorionic vessels. At the commencement of development all the maternal walls are present in the highest types of placentae also. But while the fetal layers are always retained, or, in the highest types, are gradually formed, during the early stages of development, the maternal partitions disappear one after the other in the course of the phylogenesis or ontogenesis, the chorionic epithelium penetrating farther and farther toward the source of its nutrition, the maternal blood. But the blood spaces themselves, those of the mother on the one hand and those of the fetus on the other, remain sharply separated under all circumstances. The penetration of the fetal tissue may halt at any stage and so determine the structure of the mature placenta and also the name which may be applied to it, this indicating the maternal tissue which is in immediate contact with the chorionic epithelium. At the beginning of the series stand placentae such as those of the pig, in which all the maternal partitions are retained; the uterine and chorionic epithelia are in contact; and the placenta is a placenta epitheliochorialis. If the maternal epithelium disappears, at least to a considerable extent, as in the ruminants, the chorionic epithelium comes into contact with the connective tissue and a placemta syndesmochorialis is formed. If the connective tissue also disappears, so that the chorionic epithelium is in contact with the endothelium of the maternal blood-vessels, as is the case in the Camivora, according to Schoenfeld, then the placenta is to be termed a placenta endotheliochorialis. And, finally, if the endothelium disappears, so that all the maternal partitions have vanished and the maternal blood directly bathes the chorionic epithelium, then the highest possible stage of placentation has been reached and the placenta is a placenta hcernochorialis. Thus the most important morphological character of a placenta is directly indicated by its name.

The further subdivisions may, following Strahl, be based on the form of the placenta. Thus there may be recognized a placenta diffusa^ in which the chorionic proliferations or villi are uniformly distributed ; a placenta multiplex, with the villi arranged in groups; a placenta zonaria, in which they have a girdle-like arrangement ; and a placenta discoidaUs, in which they are aggregated to form a disk-like structure. The last group, which includes the highest types of placentae (the haemochorial of the classification given above), may be divided, again following Strahl (1905), into labyrinth placentce, with narrow capillary-like channels for the maternal blood, and bowl placentce (placentce olliformes)^ in which the maternal blood has the form of a large sinus, the floor of the space (bowl) being formed by decidua and the roof by the chorion, from which the villi project, into the space. The human placenta is a placenta vera (conjugata, cumulata) discoidalis ollif ormis, or, according to my nomenclature, a placenta hcemochorialis discoidalis olliformis. It represents the highest development of its type, a development which even the placentae of the anthropoid apes have not quite reached.

The nutrition of the embryo takes place, in general, in two ways : on the one hand, by the transference of nutritive material from the blood of the mother to that of the child ; and, on the other, by the direct absorption by the chorionic epithelium of products of the maternal mucous membrane, these products frequently being subjected to a kind of digestive process before they pass into the embryonic circulation. These maternal substances are partly products of secretion, partly waste products, together with extravasated maternal blood, and have been included by Bonnet under the term embryotrophe and by English authors have been designated pabulum. In the lower types of placentae the embryotrophe plays an important role throughout the entire duration of pregnancy; in haemochorial placentae, and therefore in man, we find (as has been noted, for instance, by Pfannenstiel and Jung), at the beginning of development, up to the establishment of a definite circulation in both the maternal and fetal blood spaces, a very distinct absorption of embryotrophe consisting of degenerated maternal tissues, while later, embryotrophe is entirely wanting, at least in the region of the placenta.[6] In haemochorial placentae, therefore, two phases or stages may be distinguished : an embryotrophic phase, at the commencement of development; and a later hcemotrophic phase, not sharply distinguished from the former in time, but during which the nutritive material is received from the maternal blood exclusively.

This absorption of material cannot, however, be regarded as a simple process of diflfusion. This could be the case only with crystalloid substances at the most; colloids, on the other hand (such as the albumins, for instance), are taken from the maternal blood by a process of resorption, associated with a partly constructive and partly destructive activity on the part of the epithelium of the villi; and certain highly complex substances, such as many immunity substances, cannot pass the placenta at all. The chorionic villi of the placenta have a certain similarity to the intestinal villi (Hofbauer), the maternal blood corresponding to the digested food material. Up to the present the wandering of fat, glycogen, and iron, the last as haemoglobin or its derivatives, has been followed histologically from the maternal blood through the chorionic epithelium into the fetal vascular system. The fat, which penetrates into the chorionic epithelium in a state of solution (saponification), is reconverted into fat globules within the epithelium at the bases of its cells.[7] The haemoglobin comes from the maternal blood-corpuscles which degenerate in the placenta itself, perhaps in contact with the chorionic epithelium. Oxygen is set free from the oxyhsemoglobin of the mother, probably by ferment action (for further consideration consult Hofbauer and Kehrer). The maternal blood, therefore, often assumes in later stages, even in placentae of the highest type, the role of the embryotrophe, although not in a manner easily recognizable histologically ; and also for this reason the term haemotrophic phase is justifiable.

In placentation many cytological phenomena occur that are not observable elsewhere. The most striking are those that lead to the formation of multinucleated masses of protoplasm. Bonnet (1903) has brought order into the exceedingly confused nomenclature of these structures; he designates (Lehrbuch, 1907) as syncytia, ** deeply staining nucleated masses of protoplasm formed by the fusion of originally separate cells ; plasmodia, on the other hand, arise by repeated nuclear division unaCoompanied by corresponding cell division. . . . Syncytia and plasmodia are always living and active formations, endowed with especially energetic metabolism, together with histolytic or phagocytic properties, and also with the power of amoeboid movement. . . . They may subsequently split again into separate cell territories. . . . Quite different are the deeply staining nucleated masses produced by the confusion of originally distinct cell boundaries and by aggregation, but which show unmistakable signs of commencing degeneration,'^ Such masses are termed symplasmata.

Syncytia and plasmodia are chiefly formed by fetal tissues, namely, by the chorionic ectoderm ; symplasmata, on the contrary, arise from the maternal tissues. Yet, for a precise definition of the structure, mention should be made of its origin ; so we speak of a syncytium fetale epitheliale, of a symplasma maternimi conjunctivum, etc. If the masses in question remain relatively small they are known as multinuclear giant cells or simply as giant cells; the above classification is applicable to these also. Mononuclear giant cells, which, however, never reach a special development in the human placenta, are merely greatly enlarged cells, usually derived from the fetal epithelium.

While extensive histological modifications may affect almost all the constituents of the maternal mucous membrane and find expression there in the formation of the decidua mentioned above, these modifications affect only the chorionic epithelium among the fetal tissues, the chorionic connective tissue and vessels showing great uniformity of condition. The chorionic epithelium has been termed the trophoblast by Hubrecht; this distinguishes the ectoderm of the chorion from that of the embryo and that of the amnion. In the region of all placentae belonging to the higher types it shows, at least in parts, active proliferation phenomena. Where it comes into relation with the maternal tissues it usuallv becomes transformed at its surface into a syncytium (according to Hubrecht's terminology, a plasmodium), and this portion has been termed the plasmoditrophoblast (Vernhout, the plasmodihlast of Van Beneden), now more properly the syyicytiotrophohlast ; while those portions in which the cell boundaries are still retained form the cytotrophohlast (the cytohlast of Van Beneden).

The trophoblast in Hubrecht's sense is a morphological concept, based upon the views of that author as to the phylogenesis of the Mammalia; it occurs in all of this group and covers the entire ovum: it may also enter into entirely passive relations with the maternal mucous membrane. The term is not used in Hubrecht's sense when it is applied to the proliferating trophoblast, as frequently happens in the literature.[8] This proliferating portion of the trophoblast, which is provided with histolytic properties and especially makes possible the formation of placentae of the higher types, is quite different from the portion known as the inactive trophoblast, and has been termed by Minot the trophoderm. Only in man (and the anthropoid apes) do the two ideas coincide, since in these cases the entire trophoblast undergoes lively proliferation and is, therefore, converted into trophoderm.

Finally, as regards the position of the ovum in the uterus, different types are recognizable (Bonnet, 1903). The union of the ovum with the mucous membrane is known as the implantation or nidation. If tlie ovum remains in the main cavity of the uterus, the implantation is termed a central one. This is the most frequent type {Adeciduata, Carnivores, the rabbit, the lower apes, etc.). If, however, the ovum becomes implanted in a furrow or diverticulum of the uterus and subsequently is shut off from the uterine lumen by a fusion of the lips of the furrow or diverticulum, then the implantation is of the excentric type (hedgehog, mouse). Finally, if the ovum penetrates into the mucous membrane by producing a destruction of the uterine epithelium and develops in the mucous membrane after the closure of the point of entrance, that is to say, outside the cavity of the uterus, as in the guineapig and in the rodent Geomys, then the implantation is of the interstitial type. In man the occurrence of this last type has nowbeen almost certainly proved.

In the last two types of implantation the ovum is separated from the uterine cavity by a layer of maternal tissue, the decidua capsularis. It arises in the first case by a fusion of the margins of the walls of the furrow or of the lips of the diverticulum; in the second case, by the fusion of the lips of the implantation cavity ; and, in later stages, when the ovum bulges out toward the lumen of the uterus, it covers like a shell the part of the ovum turned away from the placenta.

II. Menstruation

Menstruation, which occurs at regular periodic intervals in man and the apes, is the expression of changes in the uterine mucous membrane which are associated with preparations for the reception of a fertilized ovum. A consideration of it is therefore necessary as an introduction to an account of placentation. The mucous membrane of the corpus uteri has, in general, a very simple structure. A single-layered, cylindrical or cubical surface-epithelium, with varying amounts of ciliation (Mandl, 1908), simple or sparingly branched tubular glands varying considerably in number in different individuals (Hitschmann and Adler), a stroma with fine connectivetissue fibrils which are diffi^ cult to demonstrate by ordinary histological methods (Bjorkenheim, Hitschmann, and Adler), and, finally, the entire absence of a submucosa — these are its most important characteristics. The ends of the glands frequently penetrate to between the irregularly defined innermost layers of the muscularis and so obtain for the mucous membrane a firm adhesion to the muscularis and a wellprotected position for their basal portions, a circumstance of considerable importance both intra and post partum.

Hitschmann and Adter[9] have shown by their comprehensive, recently published observations, upon which are based the statements that follow, that this mucous membrane is never in a completely resting condition in a fertile female. Growth and degeneration alternate regularly and form together a menstrual cycle of normally twenty-eight days. The cycle may be divided into certain more or less clearly marked periods or phases. The longest of these is the interval (between two menstruations) or the intermenstrual period, which lasts for about fourteen days, during which the mucous membrane is almost at rest and only undergoes a very gradual increase in thickness. Upon this follows, without a sharp limitation, the premenstrual period, which lasts about six or seven days and is characterized by intensive proliferation and swelling of the mucous membrane, finally leading to hemorrhages. These last for about three to five days, the period of menstruation, during which the mucous membrane again decreases in thickness and undergoes extensive degeneration. In the remaining period of the cycle, the postmenstrual period, of about four or six days duration, the mucous membrane is regenerated.

The mucons membrane during the interval is in the condition usually described as normal (Fig. 80). The mucosa is, on the average, about 2 mm. thick ; in the fresh condition it is grayish red and rather smooth. The glands have a slightly spiral course and, for the most part, are directed obliquely to the surface, their lower ends being, as a rule, bent upon themselves. Their lumina are oirfiular in transverse section and at first empty. The gland cells are at first small with elosely-set nuclei ; but in the second half of the period they become enlarged, their plasma becoming homogeneous and acidophilous. The stroma cells (Fig. 89) are fusiform or stellate, with large nuclei, richly provided with chromatin, and possess but little plasma, so that the tissue resembles adenoid or embryonic connective tissue. Lymphocytes and small lymph-nodes into in it.

Keibel Mall 079-082.jpg

Fig. 79-82.— Figures of the uterine mucous membrane in the various phases. Fig. 79. Post-menstrual mucous membrane. one day after menstruation. Fig. 80. The condition during the interval. Fig. 81. Premenstrual condition. Fig. 82. Condition on the third day of menstruation, showing separation of the superficial layer. (After Hitschmann and Adler.)

Keibel Mall 083-087.jpg

Fig. 79-82.— The form of the glands in the different phases of menstruation under the same magnification.

Already toward the close of the interval ???????????

amniotic and yolk-sack cavities) and it was enclosed by a tliick investment of tissue, which is probably to be regarded as chorionic ectoderm only, the trophoblast shell (Fig. 93). This shell, the blastocyst wall, consists (see Verk. Anat. Geseltsck., 1908) (1) of an inner lamella in which the cell outlines are not sharply detiued, the nuclei are very irregular in size, and many cells show double, treble or even multiple nuclei; (2) of an extremely inegnlar formation which has definitely plasmodtal characters. These two layers differ very markedly in the characters of the nuclei and in tlie staining' reactions of the protoplasm, but they clearly form parts of one formation. The cellular layer we name, after Hubrecht. Ilie cytotrophoblast, and the plasmodial layer, the plasmodi trophoblast. The cytotrophoblast is confined to the immediate wall of the blastocyst, and tiiere is no sign of protrusions of tlie cellular layer into the strands of the plasmodiuni, although at one or two points a minute bud of eytotrophoblast is seen estending outwards.

" The Plasmodium " forms an extremely irregular network, the spaces of which are filled with maternal blood (Fig. 94). Isolated masses of the formation show al stages of vacuolation, from niulliple small vacuoles to a spun-out reticular condition. This vacuolation of the plasm odium is probably produced by the secretion of a fluid containing digestive ferments, which cause coagulation necrosis followed by solution of the decidua, thus leading to enlargement of the implantation cavity. As the vacuoles enlarj-e tlie plaj^modium is reduced to fine strands, and when these break throtigh, the maternal blood lakes the place of the secretion in the spaces of the mesh-work."

The oval cavity of the decidua, in which the ovum lay, had diameters of 1.9 X 0-95 X 1-1 mm, A small opening, closed by fibrin, and about 0.1 mm. in diameter, placed the cavity in communication with the lumen of the uterus; the opening was not covered by a blood-clot. The wall of the implantation carity, except at points where maternal vessels opened into the cavity, was formed of necrotic decidua and fibrin deposits. Only at individual points did the Plasmodium quite reach the wall. The glands were enlarged and filled with blood, their epithelium haWng separated; and the greatly dilated vessels form, especially beneath the ovum, a regular cushion. The decidua is traversed by numerous leucocytes, and all tlie portions of the uterine mucous membrane that were esamiaed showed decidual changes. In the necrotic decidua zone around the ovum and also lying free in the blood -containing implantation cavity was an almost continuous peripheral layer of large, mostly mono-nucleated cells (Fig. 95), which are perhaps to be regarded as degenerating decidua cells set free by the breaking up of the necrotic zone." "The comparison of these cells with a layer of fetal cells which occurs upon the surface of the placental anlage in the guinea-pig, a comparison drawn by the authors on the bafli.s <)f a demonstration by Graf Spec, does not seem to be justified, since the cell layer in question (Duval's ectoplacental entodenu; see also the author's Lehrbuch) owes its existence to tlie greatly modified inversion of the germinal layers in the guinea-pig.

Keibel Mall 094.jpg

Fig. 94. — BIastocyst wall with cytotrophoblast and syncytium, decidua, and opening of a dilated sinus-like capillary in the implantation cavity. cyt., cytotrophoblast; dec., decidua; end., endothelium of a maternal capillary; n. z., necrotic zone of the decidua; pl. plasmodium (sycytium). X 2S0. (From Bryce-Teacher, Plate V.)

" Corresponds to the syncytium of Bonnet (p. 95), since it contains no nuclear

DlaoUtiooWiiy filled with blood. 3M. (F^[Il Bryoe-Teacher, FIbib VI.)

The preparation was obtained from an abortion which occurred sixteen and a half days after the only eohabitation that needs consideration and ten days after the failure of the expected menstruation. Tlie microscopic picture is very Strang* and striking and cannot be compared with any stages of placenta formation known in animals;" it ii liowever, as the niithors state, qnite reconcilable with the newer theoretical deduclions concerning implantation and the commencement of the placenta formation. Among the most sinking peculiarities in cumparisoa with what is found in older preparations are ; ( 1 ) the structure of tlie trophoblast shell; (2) the sniallness nf the implantation oj>eninp; (3) the necrotic character of the wall of the egf; eliaraber and the absence of a mutual penetration of the fetal and maternal elements. Whether the preparation can be regarded as absolutely Donnnl must provigionally be left undecided; it comes, on tbe one hand, from an abortion, and, on tbe other, it was preserved only after having remained for twenty hours in a mixture of urine and blood serum. Nevertheless, mitoses are still distinguishable la the cytotrop ho blast cells, and the geaersl impression furnished by tbe preparation, which was demonstrated at the Congress of Anatomists at Berlin, 1908, is distinctly favorable. In the absence of other equally young ova our views concerning placentation must, for the time being, be brought into harmony with this preparation.

Keibel Mall 096.jpg

Fig. 96. — A section through the Peters ovum and the surrounding portions of the uterine mucous membrane. Bl.. blood lucane: Ca„ capsularis; m.Chz., mesodermal axis of the first chorionic villi; Co., decidua compacta; Dr., glands; E., embryo; G.. maternal vessels; Sc., closing coagulum (Peter's fungoid tissue) Sy., syncitium; Tr., trophoblast; Ue., uterine epithelium; Uz., zone of enclosure. The opening in the capsularis extends from a to b. X50 (After Peters, 1899. Compare also Fig. 97.)

The conditions in the Peters ovum are quite different. The cavity of the ovum contains the magma reticulare with the antage of the embryo and the body cavities" (Figs. 96 and 07), and has diameters of 1.6X0-9X0.8 mm.; external to the chorionic mesoderm is a layer of closely packed cells, which is traversed by wide blood spaces and surrounds the entire ovum like a shell or mantle having a thickness of 0.5 mm. or more. Into this cell mantle, which is thicker toward the muscularia than toward the surface of the mucous membrane, there project everywhere short, stout processes of the mesoderm, the anlagen of the mesodermal axes of the villi. The cell mantle, on account of its relation to the mesoderm of the ovum, can hardly be interpreted otherwise than as the chorionic ectoderm, trophoblast, and trophoderm."

Peripheral to this trophoblast shell lies a layer of tissue which Peters terms the transition zone and which contains, imbedded in an (edematous stroma, a confused mass of maternal, and apparently also of fetal, cells, together with a large number of free blood-corpuscles. The entire ovum, without projecting beyond the level of the mucous membrane, lies beside a fold of the membrane.

"Whether the extensive syncytial formation described by Strahl (1906) in young stages of Miirmecaphaiia, Dasypus, Dendmhiirax. and Aluala, and by Duckworth (1!)07) in Maeacus, is comparable with that in the hnman ovum cannot be determined, since Strahl gives no figures and (hose of Duckworth concern a somewhat later Nlnge.

Keibel Mall 097.jpg

Fig. 97. — Cytotropboblut and lyncytiuDi of the Peon ovum. The embryonie >truiituT«9 an shown dii«nunm«ticallv. Ah,, uvmaiie avity: Dt., yolk mck; Ic.-H.. inUrcellulmr c&vitiaa ol the meiodemi; U.. body cavitiei (cf. Groaser: Lehrbuch); M. r„ tn««au reticulare; Sy.. lyueytium: Tr., (cytoltrophobilM. (From Peten. Plate I, copied under control of the preparation ilMlf.)

" For details concerning the formation of tbe body cavities of the Peters embryo consult Grosser's Lehrbuch. "Compare, however, the ovum of Beneke described below, and Disso's interpretation of it.

imbediJed in the decidua compacta, which over tbe dorsal surface, the summit of the ovum, is defective over an area of about 1 mm,; throughout this region the uterine epithelium, elsewhere well preserved, is wanting. The egg does not project through this defective area freely into the uterine lumen, but is separated from it by a fibrin clot that closes the opening in the compacta and spreads out lateralis like a fungus growth (Figs. 96 and 98). This clot b termed by Peters the fungoid tissue or blood-fungus, and later by Bonnet the dosing coagulum.

The decidua over tbe entire surface of the uterus is high and swollen, and is divided by furrows into distinct areas; its separation into compact and spongy layers is distinct only in the neighborhood of tbe ovum, for, although enlarged glands with epithelial papillffi occur elsewhere, yet these oCoupy almost the entire thickness of the mucous membrane, so that a superficial compact layer is not distinct. Typical decidua cells cannot be found, although some large cells of irregular shape and with large, deeply staining nuclei occur in the vicinity of the ovum; the significance of these is, however, obscure. The entire mucous membrane, in which very greatly enlarged blood-vessels occur, especially in the neighborhood of the ovum, shows signs of edematous infiltration, which increases in distinctness nearer the ovum; in this region extravasated red and white bloodcorpuscles also occur. A new formation of blood-vessels occurs especially in the zone of tissue which intervenes between the ovum and the uterine lumen. The glands in the neighborhood of the ovum cun'e around this and open near it upon the surface of the utena; beneath the ovum are closed glandular spaces filled with blood, which show no connection with the e^ capsule.

File:Keibel Mall 088.jpg

Fig. 88.— Summit o( lli« PoWn ovum. BL, blood Ucun«; Co., capnuluie: &., oli _ _ _ . St., iUiUlk; Sv., syncytium; rr., trophoblut; (7*.. uterine epithelium: l/c.R., the crumpled bolder of this; a., cropboblKt aucleue in the syncytium; b. sod c, preparatory stagea of the syncytium (wreath-like depont in blood taauna-J (From Peters, ISBB.J

A number of important points are slill to be noticed concerning the trophoblast layer. The principal part of tbe layer consists of completely separated cells with pale protoplasm and large, deeply staining, round or oval nuclei. On account of the size And staining properties of the nuclei the entire trophoblast shell appears dark even under weak magnification. Throiighout its entire extent it is traversed by blood lacunffl, some lai^ and some small, which are continuous one with the other; these lacune, some of which approach so closely to the chorionic mesoderm as to be separated from it only by one or two layers of cells, are everywhere completely filled with well-presen-ed matertiat blood. At various places they are in cotmection with venous vessels, which possess an endotlielial wall only in the transition zone; the opening of arteries or capillaries into the lacunee cannot be made out. " The most peripheral lacun» are, for the most part, separated from the decidual tissue by a thin covering of ectoblast arranged in concentric layers; but in places diverging tracts of trophoblast stream out into the compacta, and the blood spaces lying between these lack the ectodermal covering on their peripheral surfaces," In the most central portions of the trophoblast cells are to be found wilh feebly staining and distended nuclei, with vacuoles, nuclear fragments.

File:Keibel Mall 089.jpg

Fig. 89.— A portion of the peripherjof the trophoblast shell of the Peter ovum. Degenerating patsheB of syncytium with greatly enlnrged nuclei; tbe blood-corpusclea, for the mont part, only mtiag npon tbe lyooytium. Tr., cytotropboblaat; Ui., encloaiug lone. x 360.

and flakes. More peripherally the distention and degeneration of the nuclei increases, the cell boundaries vanish, and there are formed very irregular, large, vacuolated masses of protoplasm, with numerous, irregularly contoured, and exceedingly large nuclei (Figs. 99 and 102). These masses constitute the syncytium of the Peters ovum, which is, accordingly, united by all possible transitions with the cellular trophoblast; it is never separated from this by a limiting membrane. Prickle processes cannot be seen; at most there is " a delicate and thin, strongly refractive deposit, slightly frayed at the edges, on the surface of thfe syncytium." The syncytium completely clothes, except at a few ]>laces, the blood lacunie with a thin layer; indeed, according to Peters, the formation of the syncytium seems to be produced by the contact of the trophoblast with the maternal blood. Furthermore, it would seeni, according to his ideas, that degenerating red and white bloodcorpuscles may be " transformed " into a syncytium, which applies itself to that formed by the trophoblast, so that the blood with its own stnictural elements may be concerned in the formation of the syncytium (compare Fig. 98, " wrealh-like deposits in the lacune representing preliminary stages of the syncytium ")." Tlw syncytium occurs, as a rule, only at regions where there is contact with the maternal blood. Trophoblast and syncytium are frequently mingled with elements of the maternal tissues in the transition zone, and, like these, undei^ degeneration in that region, since free maternal and fetal nuclei can be found in it; the trophoblast and syncytium also frequently replace the wall of a gland and project into its lumen, and they may form the walls of the maternal blood-'Vessels in the peiipheral portions of the trophoblast shell — sometimes by forming one wall of the vessel while Ihe opposite one remains formed fay normal epithelium, sometimes in that over the entire wall only the epithelium, either intact or in fragments, separates the syncytium from the cavity of the vessel (Fig. 100). A transition between the endothelium and the syncytium is never recognizable.

Peters's preparation was obtained from the uterus of a suicide, poisoned by caustic potash on the third day after the omission of a menstrual pmod. The through At two places (a And endothelium; En., eudotheli ium," (After Peters, 1890.)

mode of death may not have been without influence on the blood engorgement of the uterine mucous membrane. Peters estimates the duration of the pr^nanc; at from three to four days; details concerning this are given elsewhere. The preservation of the ovum (the autopsy was performed a few hours after death) with the exception of the caudal end of the embryonic aniage, was very good, even although mitoses are not recognizable in the trophoblast cells. The Leopold ovum, which was obtained from a case of phosphorus poisouing, concerning which further data are not available, differs in several points from that of Peters; Thus, the trophoblast growth was less extensive ; and the blood lacunte, which were in open conneetioii with the neighboring capillaries, were unusually wide. The trophoblast cords were, for the most part, reduced to one or two layers of cells, and were to a lai^ extent covered by syncytium. In addition to the ovum, separated portions of the syncytium were also to be found in the decidua, having evidently wandered into it; but, on the whole, there was less syncytium than in the Peters ovum, and its individual parts were smaller. It was everywhere clearly distinguishable from the vascular endothelium. The contents of the trophoblast shell, the mesoderm of the ovum, were irregularly shrunken and contained maternal blood-corpuscles; an embryonic anlage could not be distinguished (it had probably been already destroyed). The internal diameters of the cavity of the ovum were 1.4 X ^-^ X 0.8 mm. This ovum was also imbedded, somewhat superficially, in the mucous membrane in the neighborhood of a furrow, but a differentiation of the mucous membrane into compacta and spongiosa was not distinct. The regions surrounding the ovum were very rich in glands, which curved around the ovum. Dorsal to the ovum the decidua, in contrast to that of the Peters ovum, is closed except for a small opening, so that a decidua capsularis is present. Extending outward from the opening upon the surface of the mucous membrane is a clot, consisting of blood and fibrin, which corresponds to the fungoid tissue or closing coagulum and is termed by Leopold the fibrin cover.

" Peters, in a private communication, now regards these and similar structuree as rather the expression of embiyotrophic processes.

On account of the absence of the embryonic anlage the stage of development cannot be aCourately determined; the measurements are not sufficient for this purpose, since, as has been pointed out, the contents of the ovum were shrunken and the blood lacunae enormously distended. The relatively scanty growth of the trophoblast may indicate, as Bryce and Teacher remark, that the ovum was younger than that of Peters; the small size of the opening in the capsularis may also have the same significance (see below, p. 117). However, definite conclusions cannot be drawn from the preparation. The ovum described by Stolper (1906) seems to represent a very young stage, but it had evidently died some time before its abortion. The diameters of the egg capsule (2.5 X 2.2 X 1-0 mm.) are, at all events, smaller than in the two ova to be described next, but for which the corresponding measurements are not given. The embryo was macerated. The ovum is characterized by a very extensive development of syncytium. Wide blood spaces, probably intended for a diminution of the blood pressure in the communicating vessels, are regularly arranged around the intervillous space.

The results obtained by Graf Spee (1905) from a young ovum studied by him have been stated only briefly, and until a thorough study of the ovum and figures are available, a comparison with the ova already mentioned cannot be made. The ovum was obtained from a case of oxalic acid poisoning; the mucous membrane of the uterus " showed the areas, di\'ided by furrows, that are characteristic of pregnancy," and in one of these at a point marked by a slight depression of the surface was the ovum. " Beneath about two-thirds of the free surface of the prominent area of mucous membrane, imbedded in a cavity in the interglandular connective tissue of the uterine mucosa, was an ovum measuring 1.5 X 2.5 mm. in its greater diameters, poorly provided with villi, and with very small embryonic structures in the anterior. Between the surface of the chorion and the uterine tissue were here and there small quantities of blood from open blood vessels. The walls of the egg chamber consist throughout of elements of the interglandular connective tissue of the uterus. The lumina of all the glands open into the uterine lumen; none into the egg chamber. The portion of the mucous membrane (serotina) intervening between the ovum and the muscularis holds a large mass of blood (just as in the ovum of Peters) contained in enormously enlarged endothelial canals and apparently stagnant even in life ; it may very well have furnished nutrition to the ovum and at the same time have served as a rampart protecting the parts of the mucous membrane near the muscularis from the destructive contact action of the ovum. The walls of the egg chamber, separating the ovum from the lumen of the uterus, consisted of a thicker or thinner layer of the interglandular connective tissue next the ovum "and a single-layered epithelial covering next the uterine ca\nty. Only in the region of the surface depression is the uterine tissue interrupted by an opening; which may be regarded as the point of entrance of the ovum iato the uterine mucous membrane, the implantation opening; it is closed only by a flat expanded blood-clot (fibrin with enclosed leucocytes and red blood-corpuscles). The conditions are, accordingly, very similar to those occurring in the human ovum described by Peters.

'^ The implantation opening, at this stage 0.8 mm. in diameter at the most, has probably increased somewhat in size from what it was when first produced by the ovum by stretching and growth, and perhaps also by histolysis of the chamber wall, for I imagine that the ovum during the seven days which probably intervene between fertilization and implantation cannot have increased much in diameter and therefore cannot have measured much over 0.2 mm."

Among these data the most striking are the small amount of blood in the immediate neighborhood of the ovum and the small number of villi. Nothing is stated concerning the character of the chorionic epithelium, the syncytium, and the intervillous space. The ovmn, nevertheless, does possess villi and in this respect is further developed than Peters's preparation. It is questionable, however, if it is to be regarded as quite normal.

The ovum described by Jung agrees excellently in its general character with that of Peters. It was obtained from a curetting, and, completely surrounded with mucous membrane, was preserved, while still fresh, in 80 per cent, alcohol. Its age was not determined.

The egg capsule was completely separated from the lumen of the uterus, but was situated somewhat superficially. The somewhat compressed but uninjured cap of the ovum was composed of coagulated blood and tufts of fibrin, together with numerous leucocytes and degenerating decidua cells, and passed gradually over into the transition zone. The diameter of this necrotic cap was 1.7 mm.; it corresponds, according to the opinion of the author, to the closing coagulum of other ova and its extent indicates that of the distended implantation opening.** The diameter of the ovum exclusive of the chorionic epithelium was 2.5 X 2.2 (X1.1) mm.

The mesoderm of the chorion had already sent processes, the mesodermal axes of the villi, into the extensively developed trophoblast (Jung avoids the use of the term trophoblast and speaks only of ectoblast). The ovum was completely surrounded by rudiments of vilH, all of about the same length; and on the chorion membrane and at the roots of the villi was an epithelium, consisting of two layers, a basal and a covering layer. The basal layer, composed of distinctly defined cells, passed over into stout columns of cells, which frequently united and so formed the shell around the ovum. Only occasionally did free cell-columns occur, the representatives of free villi. In the peripheral portions the individual cells were somewhat larger and clearer, but everywhere abundant mitoses could be observed and there were no signs of degeneration in the peripheral elements. Individual mitoses were so placed that one of the daughter cells passed into the covering layer, this, the syncytium, showing no mitoses although the nuclei were, for the most part, well presented. The protoplasm of the covering layer presented, in general, a foamy structure; prickle processes projected toward the intervillous space, at least in certain places. Only at certain regions of the periphery was the covering layer, which frequently streamed into the maternal tissues, in degeneration and forming a symplasma syncytiale in Bonnet's sense, perhaps as the result of the action of maternal leucocytes. The vacuoles of the covering layer at places contained what seemed to be altered maternal blood, but everjrwhere a continuity of the syncytium with the maternal tissues, that is to say, with endothelium, was lacking. The boundary between the maternal and fetal tissues was almost everywhere easily recognizable, with some difficulty only in the regions where symplasma structures occurred.

"In this case the capsularis would not actually be closed. The gradual transition of the cap into the transition zone on the lateral portions of the ovum seems to be opposed to Jung's view. It is possible that the capsularis had at one time been complete, but was again undergoing degeneration.

Between the trophoblast columns, that is to say, the anlagen of the villi, there was a very irregular intervillous space ; this was abundantly tilled with blood, was in continuity with the maternal vascular system by means of gaps in the sieve-like trophoblast shell, and was lined by maternal tissue (endothelium) only in the neighborhood of these gaps. The communications with the maternal vessels were always narrow and the circulation must have been very slow. In the transition zone, situated outside the trophoblast shell, degenerating maternal tissue occurred, partly associated with the formation of symplasmata, but always without signs of active proliferation; also no new formation of blood-vessels could be found. Around the ovum was a strip of fibrin of varying thickness, produced by degeneration of the maternal tissue (stroma, endothelium, gland epithelium). Leucocytes occurred abundantly in the transition zone, but not in the fetal tissues. The glands were frequently destroyed by the trophoblast, but appeared to withstand its attacks for a longer time than the rest of the decidua; none of them opened into the intervillous space, but they took a curved course around the ovum. External to the transition zone a separation of the compacta and spongiosa had taken place. The former was oedematous, beset with numerous lymphocytes, and its gland ducts were contorted; typical decidua cells and hemorrhages were wanting, although the glands frequently contained clotted blood. The representatives of the later decidua cells showed numerous mitoses. No oedema occurred in the spongiosa.

The ovum of Beneke was obtained from a curetting twenty-five days after the omission of a menstrual period and was fixed in alcohol. It contained an embryo measuring 1.86 mm. in length, and had a cavity of 4.2 X 2.2 X 1*2 mm., surrounded by a trophoblast measuring 0.4-1.0 mm. in thickness. " As regards the structure of the trophoblast the author can only confirm in general the observations of Siegenbeek, Peters, Marchand, and others.** The syncytial giant cells are throughout of fetal origin and symplasma formation is not recognizable. The sjmcytia had encroached upon the endothelium of the decidual vessels and also upon the epithelium of the glands; by the development of extensive clefts in the interior of the giant cells the intervillous blood spaces are being formed. Scattered giant cells with prickle processes occur in the chorionic connective tissues of the investment of the oviun; they wander to a certain depth into the decidual tissue, where they may be recognized by their characteristic nuclei and by containing glycogen. The decidual cells, extensively swollen, take part in the formation of the so-called transition zone to a greater extent than has been supposed by Peters, for example. The closing * tissue plug ' which fills the opening in the reflexa corresponds in general in its histological constituents, blood, fibrin, leucocytes, etc., with what Peters has described."

The measurements of Siegenbeek's ovum (4.5 X ^-^ mm.) were not made directly, since the ovum had been opened by a tear at one spot and was collapsed[10] but were estimated from the perimeter. It was obtained from a woman who had met an aCoidental death from burning; the entire uterus was preserved in formalin fourteen hours after death. The ovum was completely covered with villi, those on the basal surface being stronger than the peripheral ones, and those about the equator of the ovum the strongest of all. Free villi occurred; the majority were continued into cell columns (ectoblastic trabeculae), which united together peripherally and formed an ectoblast shell traversed by large and small spaces, and varying in thickness in different regions. In general it was thicker on its peripheral than on its basal side. The ectoblast cells situated near the maternal tissue were larger than those having a more central position and frequently showed degenerating nuclei, but mitoses occurred in all portions of the ectoblast shell. The boundary between the fetal and maternal tissues was difficult to make out in certain regions. The intervillous space was formed by blood-filled lacunie which were lined only by cellular ectoblast or by syncytium; the endothelium was also frequently wanting in the blood-vessels at their communication with the intervillous space. In the space were very many leucocytes and perhaps also special nucleated elements of the maternal blood. The syncytium was only to be found in the region of the blood paths; it showed no prickle processes and no cuticula on the side next the ectoblast. The derivation of the syncytium from maternal tissues (endothelium, epithelium, or connective tissue) was excluded, but its continuity with the cellular ectoblast could not be made out, so that the origin of the tissue could not be determined.

The ovum lay in the compacta, whose basal portion had the same structure as the capsularis (reflexa), except as regards the occurrence of glands. The capsularis, for the most part, lacked an epithelium and contained in its interior fibrin stria?. Basally there were greatly distended glands filled with blood; around the periphery of the ovum the glands were arranged concentrically, and the glandular epithelium did not fomi syncytia. Characteristic decidual cells were nowhere present. A sharp separation of the compacta and spongiosa had not yet occurred in the decidua vera; the compacta was (Edematous."

The ovum of Rossi Doria was obtained from an abortion. It was injured by a tear and does not seem to have contained an ernbiyo. The egg membranes were rather well presened. The theoretical considerations of the author will be discussed in note 23. Frassi's ovum was obtained from an operation fourteen days after the omission of a menstrual period; the unopened uterus was preserved in formalin. The ovum of Friolet was also obtained from an operation and fixed in the unopened uterus. Both ova already showed, for the most part, a twolayered epithelium over the villi; a criticism of the observations made upon these ova will follow in the resume.

The ova of Peters, Jung, Beneke, and Siegenbeek, with their extensive development of the trophoblast, fonn a single harmonious group, which may be derived from conditions such as Bryce and Teacher have described. To the older stages, on the other hand, a natural and easy transition is formed by the Siegenbeek ovum.

B. Resume of the first Processes of Development up to the Formation of the Villi and the Appearance of the Intervillous Space

From the foregoing the course of the first stages of developn ment may, with a good deal of certainty, be concluded. Especially is this so with regard to the implantation of the ovum. Of the types of implantation mentioned in the introduction the interstitial is the only one that concerns us here; as in the guinea-pig, so in the human species, the ovum penetrates like a parasite, through an opening that it forms for itself, into the mucosa and develops there (Berry Hart, Graf Spee, Von Herff, Peters ^^). It must at this time be very small, since otherwise such a penetration of the entire ovum could not be readily understood. The opening in the surface of the mucous membrane had a diameter of 0.1 mm. in the Bryce-Teacher ovum, in that of Leopold its margins were in contact, in that of Peters its diameter was 1 mm., and in that of Graf Spee 0.8 mm. It is probably enlarged very quickly by the growth of the ovum, and the diameter of the ovum at the time of implantation is probably about 0.2 mm. (Graf Spee). The formation of the mesoderm cannot have begun, and it is questionable if at this time even the cavities of the ovum (the blastoCoel, medulloamniotic cavity, cavity of the yolk sack) have appeared. The ovum of the guinea-pig forms at the moment of implantation a solid cell mass (Graf Spee). A marked growth of the ovum is dependent on favorable conditions of nutrition, and these are furnished only after implantation. The ovum does not undergo implantation in a furrow,^^ but at any portion of the smooth mucous membrane where perhaps a special thickening or an extravasation of blood, which may serve as an embryotrophe, facilitates implantation. The spot is usually on either the anterior or posterior wall of the uterus, and determines the situation of the placenta. The implantation usually occurs between two glands, and the glands are later forced apart by the growth of the penetrated ovum, so that they bend around it in curves. Implantation in a gland is not probable, since the diameter of the ovum is always greater than that of the lumen of a gland. During the implantation the superficial epithelium and connective tissue are dissolved and probably serve the ovum as embryotrophe ; the solution of the maternal tissues may perhaps be produced by the action of ferments secreted by the ovum, and to this Bryce and Teacher refer the vacuolation of the sjTicytium seen in young stages. The penetration of the ovum is not determined by gravity, since the minuteness of the ovum places this out of the question and, furthermore, the implantation takes place just as often contrary to the direction of gravity as in accordance with it on either of the opposite walls of the uterus. Nor can the action of an internal pressure by the uterus (Pfannenstiel) be assumed, since the ovum floats in a quantity of detritus which it produces and which cannot flow away on account of the swelling of the mucous membrane, but is rather increased in quantity by the flow of additional material from neighboring tissue spaces. There remains then only the supposition of an active penetration on the part of the ovum which may be due to an amoeboid activity of the superficial cell layers of the trophoblast (Peters), in favor of which evidence has been obtained within recent times. Indications of an active penetration by the ovum have also been furnished by young tubal pregnancies (Filth, Aschoff, and others), in which the ovum has completely destroyed the thin mucous membrane and has penetrated into the muscularis. The fact that the tube is open at one extremity is ample evidence of the non-existence of an internal pressure which could force the ovum into the muscularis. The duration of the implantation process, which in the guinea-pig is about eight hours, may be estimated at about one day in man (Graf Spee).

"The ovum has more recently been studied by Veil (1905) ; the author has not been able to accept the idea of an active penetration of the ectoderm into the maternal tissues.

"Rossi Doria believes in a kind of combination of penetration and circumvallation, since the ovum observed by him projected, for the most part, beyond the level of the mucous membrane. The ovum was, however, much too old to settle the question. He had to do, apparently, with a superficially implanted ovum.

    • The mucous membrane of the non-gravid uterus never shows, even at the greatest development of the premenstrual swelling, a formation of furrows and elevations (compare Hitschmann and Adler) ; consequently the idea, frequently expressed, that the implantation takes place in a furrow, as in the hedgehog, fails. The formation of furrows is actually a symptom of pregnancy (Graf Spee) and as such may direct the attention to the possibility of a young pregnancy in autopsies, at a time when the ovum itself can scarcely be recognized. The furrows are not preformed, but are produced as foldings of the continually thickening mucous membrane.

As to the behavior of the ovum before implantation we rely solely on conjecture based on a comparison of what occurs in animals. The fertilization of the ovum set free from its follicle probably takes place, as a rule, in the pars ampullaris tubaB, to which the spermatozoa penetrate and where they may remain capable of fertilization for days or perhaps for weeks (see, for example, His: "Anatomic menschlicher Embryonen," vol. ii). The fertilized ovum then wanders down the tube and through the uterus until it reaches the place of implantation ; this movement is a passive one on the part of the ovum, being caused by the action of the cilia of the surface of the tube and uterus. During this time the ovum loses its corona radiata ^® and zona pellucida, and passes through the first stages of development, that is to say, the segmentation; it obtains the necessary oxygen from the serum which moistens the mucous membrane and perhaps employs the secretions of the membrane as embryotrophe (p. 119). The passage through the tube to the implantation region is by no means rapid; even in the white mouse, where the distance to be traversed is very short, it oCoupies five or six days (Sobotta, Melissenos), in the guinea-pig seven days (Graf Spee), and in larger animals, such as the cat, dog, pig, and sheep, from eight to ten days (Bonnet). Taking into account the length of the human tube, the assumption that the wandering of the human ovum oCoupies eight or ten days is quite reasonable, notwithstanding that the human ovum is relatively small and the rapidity of the wandering increases, in general, with the smallness of the ovum (Minot places the wandering period at eight days, Graf Spee at seven days, Pfannenstiel at from five to seven days, and Bryce and Teacher at seven days).

Of the various' phases of the menstrual cycle, the premenstrual is the most important for implantation; at least so the study of the phenomena of menstruation seems to indicate. The premenstrual loosening of the tissues would favor the penetration of the ovum, the secretion of the glands would serve as embryotrophe until the completion of implantation, and the mucous membrane of the uterus in the cases of Peters, Leopold, Jung, and Siegenbeek resembles much more a premenstrual membrane than a decidua. The connectivetissue cells are, in Peters 's case, for example, less plainly altered toward the decidual condition than they are normally immediately before the appearance of the menses, and this even although the time of menstruation was several days overdue.^® Indeed, even in older ova, such as that of Frassi, typical decidual cells occur only in the neighborhood of the ovum ; and among all the young ova a distinct decidual alteration is to be found only in that of Bryce and Teacher. We must assume that the implantation exercises an inhibiting effect on the premenstrual changes, for otherwise menstruation would not be omitted during pregnancy ; and the delaying of the decidual changes in the uterine connective tissue may be regarded as the visible expression of this inhibition. Yet a certain amount of time must be granted the ovum for the development of this inhibitory action ; an ovum implanted immediately before menstruation may well be sacrificed to this process; and such menstruations would then perhaps be abundant in quantity. Normally (typically) therefore the implantation must take place several days before the time for the appearance of the menses, but whether two or five days previously cannot at present be determined. Perhaps two days is too short an interval to allow the inhibitory action to become efficient.

If the times required for the passage through the tube, the implantation, and the inhibition of menstruation be added together, it follows that the expulsion of the ovum from its follicle and its fertilization must normally occur at a minimum of about from eleven to fourteen days before the date of the expected menstruation. But this entire interval has been almost always neglected in gyna?co]o2:ical literature, in accordance with the tables established by His, and the age of the ovum has been determined from the estimated time of appearance of the omitted menstruation. Consequently nearly always the age estimates have been too low by the amount given above. The interval between implantation and the beginning of the expected menstruation has been considered by Peters and Leopold, for instance, but they neglected the time required for the passage through the tube. If one reckons from the moment of fertilization, the Peters ovum must have been at least fourteen days old (and implanted for about five days).

"The theory of Hofmeier that the corona radiata is retained and becomes transformed into the syncytium is of only historical interest.

    • The decidual cells are in any event to be derived from the stroma cells of the uterine mucous membrane, and the various older theories (derivation from perivascular cells, the now almost forgotten " perithelia," or leucocytes, etc.) are negligible. Concerning the mitoses observed by Jung in the preparatory stages of the decidual cells it is to be remarked that they furnish an explanation of the at first rapid increase of the decidua.

Implantation may, however, be possible in other phases of the menstrual cycle than the premenstrual, and it may be that the stimulus arising from the ovum may also have the property of aCoelerating the occurrence of the premenstrual changes. Perhaps certain pathological phenomena may be associated with precocious implantation (see Grosser '*Lehrbuch'^).

The view stated here is, however, scarcely in agreement with the age estimates that have so far been published of various young human ova. Bryce and Teacher, on the basis of an analysis of twelve cases, reach conclusions quite at variance with that given above, — namely, that menstruation is actually without influence an conception and implantation; that, indeed, the latter may take place on the day immediately before or after the calculated date for the first omitted menstruation; and that, accordingly, it is not the implantation that is responsible for the inhibition of the approaching menstruation, but the fertilization which has already taken place in the ampulla of the tube. These authors, however, start with the assumptions that fertilization occurs, on the average, twenty-four hours after coition, and, secondly, they base their calculations on a series of aborted ova as well as upon some others which were obtained by operative interference necessitated by pathological conditions of the uterine mucous membrane. If one considers, on the one hand, how much uncertainty exists regarding the time relations of the processes of fertilization and, on the other hand, the fact that only two cases of normal pregnancies terminated by extrinsic causes (Peters, Reichert) occur in their tables, it may seem venturesome to set aside as without significance the relationship of the premenstrual mucous membrane to the decidua, which is capable of being directly observed. Cases in which a spontaneous abortion occurred or in which there was a catarrh of the mucosa which called for curetting and which, if longer continued, would have produced a spontaneous abortion, may, indeed, be associated with an implantation in an improperly prepared mucous membrane. The occurrence of typical decidua in the Bryce-Teacher ovum is strange when compared with other results (see p. 119). But at all events these authors have rendered the service of having thrown full light upon the obscurity which prevails concerning the course of the phenomena under discussion.

The normal period of ovulation is also still quite uncertain. Ovulation may take place at any time ; the prevailing view is that it coincides with menstruation ^^ ( see Nagel : ' ' Handbuch der Physiologic"), while -\ncel and Villemin (1907), on the ground of their observations of freshly ruptured follicles, suppose that it occurs, on the average, twelve days before the beginning of menstruation. The latter period is in excellent agreement with the view that the premenstrual phenomena are preparations for pregnancy; this can hardly be said of the former one.

The ovum ceases its penetration in the decidua compactaj the implantation opening is closed by the coagulation of the tissue liuids exuding from the mucous membrane, and the product of this coagulation is the closing coagulum (fungoid tissue, fibrin cover) which occurs in a whole series of young ova (Peters, Leopold, Beneke, Graf Spee) and, consequently, can hardly be regarded, as Pfannenstiel would wish, as an abnormal occurrence. In the Bryce-Teacher ovum the coagulum is wanting and the authors suppose that it is first formed after the ovum has increased in size and the implantation opening enlarged. The implanted ovum begins to grow rapidly and presses further into the mucous membrane, so that it divides this into a superficial and a deep layer (Fig. 101). The superficial layer becomes the covering of the o\nim on the side toward the cavity of the uterus, it becomes the decidua capsnlaris,^^ which at first bears the implantation opening, "according to Leopold and Ravano (Archiv f. Gyn., vol. Ixzxiii, 1907) ovulation coincides with menstruation in about two-thirds of the observed cases, but in one-third of them it occurred quite independently of it ; conception is possible at any time. The authors estimate the period of ovulation from the condition of the corpus luteum; but this estimate must necessarily be uncertain, since, in view of the uncertainty of the time of ovulation, a basis for a thorough knowledge of the time required for the development of the corpus luteum is lacking. Also the observations of H. Bab (Deutsch. med. Wochenschr., 1908) indicate that impregnation, and consequently also ovulation, takes place some days before menstruation; nevertheless, it is as yet hardly possible to draw conclusions as to the time of impregnation from the size of the embryo, as this author does. Compare, for instance, the data furnished by Bab concerning his first two cases with those given by Tandler (Anat. Anz., vol. xxxi, 1907) concerning an almost equally developed embryo. The discussion whether the ovum belongs to the first omitted (Lowenhardt-Sigismund) or the last completed menstruation, a discussion in which Bab declares himself in favor of the former idea, arises from the old notion that ovulation and menstruation, on the one hand, and fertilization and implantation, on the other, coincide. The latter coincidence has been disproved ; the former is improbable, or at least requires demonstration.

" The decidua capsularis is the decidua reflexa of the older terminology. The latter name is an expression of the older theories (W. Hunter, Reichert) of its origin, to the effect that the mucous membrane was reflected or curved over the ovum and fused over it. Since, however, young stages are opposed to this view and older ones show no conditions that cannot be explained as well or even better as the results of interstitial implantation, this theory, which up to ten years ago was the only prevailing one, is now regarded as disposed of but later completely closes (see below). The deep layer, or what remains of it, forms the basis of the later placenta and is the decidua basalis (the decidua serotina of the older nomenclature) ; lateral to the ovum is the decidua marginalis, whose fate is of great importance for the later stages of development. The remaining mucous membrane forms the decidua vera, recently very appropriately termed the decidua parietaiis by Bonnet.

Fig. lOl-'-Pregnancy of the first montli. The ovum Fxpellfd with the entirededdiu; tbideddiu cBpsulariB sad chonon hnva been cut Ihrough and the intervillouji apace and extn-embryonic body-cavitjr opened. Ch,, thoi'mn; D:., decidua caps ularis^ Dp., decidua parietaiis; £., embryo in amnion. X 11 There are four structures that still require thorough discussion : the trophoblast shell, the syncytium, the blood lacunae, and tlie transition zone. The tropiiohlast shell is to-day regarded unanimously, if we neglect Pisse's view, as embryonic ectodermal tissue, as trophoblast (cytotrophoblast, trophoderm).** To it is also generally ascribed the power of dissolving and absorbing the maternal tissues. Also analogies for the fact that it surrounds the ovum as an extensive growth are to be found among animals, namely, in the hedgehog.^^ That during its growth toward the maternal tissues portions of the trophoblast also are destroyed,®^ and that a zone of mutual penetration by the tissues, a transition zone, occurs, are also phenomena frequently to be observed in animals. The trophoblast shell usually develops more extensively on the basal side of the ovum, where the nutrition is best (Peters), and there, for the same reason, are formed the embryonic anlage and, later, the placenta ^^ (Von Franque, Peters). The syncytium and the hlood lacunce are associated topographically and perhaps genetically also. The former has been the most disputed tissue in the whole field of histology, and even to-day it is not yet thoroughly understood. Of the different opinions as to its origin that have been advanced from time to time only two need further consideration ; ^^ the one derives the syncytsyncytial covering.

" The view advanped at one time by Lanp'hans, but since relinquished, that the layer of separiite cells upon the surfaces of the villi, arising' from the trophoblast, was derived from the fetal mesoderm and that only the syneytium corresponded to the chorionic ectoderm has recently (on the last oCoasion in 1904) been revived by Van der Hoeven, but without sufficient evidence.

    • The investigation of the hedgehog we owe to Hiibrecht and his school. In the literature only the first work on this animal^ that by Hubrecht himself (1890), is generally known. according to this certain important differences exist between the hedgehog and man, but more recent observations made by Resink imder Hubrecht's direction (1903) have corrected a number of inaCouracies and thereby revealed a greater resemblance to the hvunan conditions. For instance, the tissue formerly termed the trophospongia and derived from the decidua is now assigned to the trophoblast. (See also Grosser: Lehrbuch.)

" Jung, in agreement with Langhans, will not admit, at least in young stages, the occurrence of a destruction of the peripheral portions of the trophoblast shell, described especially by Peters. This author's results are regarded as postmortem phenomena.

  • This superiority of the basal growth is not always pronounced ; apart from the Bryce-Teacher ovum, which showed an especially strong equatorial development of the syncytium, there was in the Jung oviun an almost equal development of the trophoblast shell, in the Spee ovum villi occurred on the peripheral surface, and in the Siegenbeek ovum there was again a superiority in the equatorial villi. A purely equatorial villous girdle, such as the frequently figured Reichert ovum (1873) showed, cannot be regarded as normal, since it can hardly be reconciled with the idea of inter^itial implantation. The occurrence of variations within certain limits is, however, not unthinkable, since they may be produced by factors extrinsic to the ovum, such as the distribution of the embryotrophe, local pathological changes in the mucous membrane, etc.

" So long as the mechanism of implantation was unexplained, speculation concerning the origin of the syncytium had free rein. The early view, supported by the most prominent investigators (Langhans and his school, Strahl) and which a*ssigned its origin to the uterine epithelium, is irreconcilable with interstitial implantation. Also the glandular epithelium need hardly now be considered as a possible source. For a consideration of the early views consult, for example, the well-known account of Waldeyer, also Peters and Strahl. Directly opposed to the idea of its origin from the uterine epithelium are cases of pathological implantation, such as are seen in ovarian pregnancies, for in these the villi have a typical iuin from the trophoblast, the other from the endothelium of the maternal vessels.^^

The trophoblastic origin of the sjTicytium is upheld by all supporters of Hubreeht's views and especially by all recent students of the problem. The Bryce-Teacher ovum is especially illuminating in this connection : in it a connection of the syncytium with the cytotrophoblast is, on the one hand, clear; and, on the other hand, an anchoring of the ovum to the maternal tissues, that is to say, a direct contact of syncytium and decidua, is wanting. Peters, Leopold, and Jung expressly mention the occurrence in their preparations of gradual transitions between the cytotrophoblast and the syncytium (for example, the passage of nuclei from the former into the latter, Jung) and the absence of similar transitions between the svncvtium and the endothelium. These facts overthrow the opposed view of Pfannenstiel, based upon older preparations, which view brings him into aCoord with a number of older authors and for support of which he relies upon one uterine ovum which he himself investigated and one tubal ovum; at the same time other authors, such as Frassi and Bonnet, find no support from older ova for an origin of the syncytium from the endothelium, but declare themselves in favor of its fetal origin. The figures given by Pfannenstiel, which seem to speak for a derivation of the syncytium from the endothelium, are, apparently, capable of another interpretation (Frassi).

But although the fetal origin of the syncytium is no longer doubtful, the beginning of its formation has not yet been sufficiently studied. Hubrecht, Marchand, Bonnet, and others suppose that the syncytium is the expression of a special vital energy and is produced by the penetration of the trophoblast into the maternal tissues. Peters, however, is of the opinion that the syncytium is formed from the cytotrophoblast by a kind of degeneration process influenced by tlie maternal blood. The syncytium of both the Bryce-Teacher and the Peters ovum ^^ is undoubtedly materially different from that of later stages, which forms a layer of almost even thickness over the chorionic villi. In the Bryce-Teacher o\nim there is a thick spongy syncytium shell resting upon a thin layer of cytotrophoblast; in the Peters preparation there is a great quantity of cytotrophoblast and a very irregular distribution of the syncytium. This forms often large masses, which frequently project freely into tlie blood, and at many places are provided with relatively few, but greatly enlarged, nuclei, so that, as Peters points out, they give the idea not of a progressive but of a regressive form of tissue and according to Bonnet's terminology deserve to be termed syniplasmata (Figs. 99 and 102). Only at certain places does the sjTicytium form a lining for the blood lacunie, so as to recall well-known figures. In the Leopold o\Tim, on the other hand, it has many more of the usual characters; still more pronounced, perhaps, is this condition in the Jung ovum, in which degenerating syncytium, termed symplasma syncytiale by the author, can be observed only locally. Following a view similar to

    • Graf Spee does not express himself definitely on the question, but from the remarkable occurrence in one instance of a cuticle between the syncytium and the cell layer he is rather inclined to aCoept a maternal origin for the syncytium, deriving it eventually from the giant marrow cells of the mother. This idea is no longer tenable.

" The author is greatly indebted to Professor Peters for permission to study and make use of this valuable preparation.

Fig. 102.— A pnnion ot lh« tn>phoblB-<t shell of the Petera ovum. The ^yncylixm hH< h me!-h-1ikc sr that of Bryce and Teacher, and as.suming that their ovum was quite normal, we may suppose that two generations, so to speak, of syncytium are formed. The first is associated with tlie implantation and with the intense histolysis which leads to tlie formation of the cavity of the e^g capsule; it is represented by the syncytial shell of the BryceTeacher ovum. Later this syncytium degenerates, for the most part, and the cytotrophoblast assumes largely the function of breaking down the decidua. In this way the appearance of the sj-ncytlum of the Peters ovum may be explained; as a matter of fact, one finds in this ovum in some regions what is almost entirely degenerating sj-ncytium, and in others a syncytial system of trabeculse with enclosed blood-containing lacunae, comparable to those of the BryceTeacher ovum (Fig. 102). Also the absence of prickle processes on the syncytium of both the youngest ova is perhaps referable to these conditions. With the gradual development of a circulation in the blood lacunae the syncytium — perhaps a new, second generation of it — assumes the task of extracting nutrition from the blood stream. Then one finds the syncytium almost exclusively in contact with the maternal blood (Jung, Siegenbeek), and only later can one again perceive an active penetration of the syncytium into the maternal tissues (Voigt, 19(35, also in the formation of syncytial giant cells; see p. 148). The absorbing syncytium then possesses prickle processes.

At all events the syncytium has one very important peculiarity ; it prevents, just like living vascular endothelium, a coagulation of the blood in contact with it and so makes possible a circulation of blood in the lacunae. Yet this peculiarity is assumed also by the cytotrophoblast, at least at the time of the opening of the maternal capillaries, since (as, for example, in the Peters ovum) this tissue forms in part the boundaries of the lacunae. Hofbauer suggests that the prevention of coagulation depends upon a layer of albumose deposited on the syncytium.

As regards the formation of the hlood lacunce, Bryce and Teacher are of the opinion that large vacuoles form in the syncytium, which at first contain a ferment destined for the solution of the decidua, but later, when this is expelled, the cavities of the vacuoles become filled with maternal blood. In this way the sponge-like infiltration of the syncytium mantle with blood is explained. Peters supposes them to be formed by the blood streaming out under pressure from the vessels opened by the trophoblast and excavating for itself, as it were, channels in the trophoblast; since, according to his views, contact with the blood determines the formation of the syncytium, it is easy to understand why the cytotrophoblast remains uncovered by it only at a few places. However, an active separation of the trophoblast cells and a subsequent filling of the lacunae so formed is possible, as Frassi points out, and such an idea receives support from what occurs in animals {e.g., in the rat). In the preparations of Peters and Leopold the lacunae are gorged with blood, but this may be the result of the mode of death, since in the Jung ovum the amount of blood is not excessive; at all events blood is to be regarded as the normal contents of the lacunae. They are the advance stages of the subsequent intervillous space, which may be defined as a vascular cavity bounded by fetal elements but filled with circulating maternal blood.^® The lacunae break up the trophoblast shell into individual trabeculae and cords, which give the entire chorion a villous appearance and may be termed primary villi.

" Remains of maternal tissue, as for example the peripheral endothelial walls of the opened capillaries, occur only on the outer sides of the space; see also Fig. 100.

Concerning the transition zone the following may be said, briefly : The name was first employed in connection with the human ovum by Peters, being borrowed from the description of the processes occurring in the placentation of Carnivora (Strahl). In early stages (Bryce-Teacher) the zone is wanting; the ovum forms a place for itself by fermentative solution of the maternal tissues.^^ Only later, in association with the disappearance of thf^ syncytial shell, already described (p. 125), does the phagocytic activity of the trophoblast become pronounced, and the fetal cells penetrate between the maternal ones and form the frequently incomprehensible complication that authors have described. In the transition zone fibrin^® also first appears. Bryce and Teacher describe a zone of coagulated, necrotic fibrin around their ovum ; in Peters 's preparations actual fibrin is completely wanting ; only the degenerating syncytium frequently resembles placental fibrin and occurs frequently in striae near the transition zone. Such transitions of the syncytium into '^fibrin" are also described by Marchand (1903) in young ova. Jung speaks of a distinct streak of fibrin which he compares to the Nitabuch stria (see p. 151) ; but in somewhat older stages such streaks are not typically present (compare Frassi). Necroses of the transition zone occur at first, accordingly, in rather variable amounts, and typical fibrin striae probably occur only after the cessation of the phagocytic activity of the trophoblast.

III. The Stages from the Appearance of the Villi to their Complete Formation

With the development of the blood lacunae means are provided for the nutrition of the embryo from the maternal blood; the purely embryotrophic stage gives place to a transition stage that will lead to the haemotrophic stage. At the same time the ovum undergoes a very considerable enlargement. The processes occurring in the transition stage which require further consideration are, chiefly, the mode of enlargement of the ^gg chamber, the closure of the decidua capsularis, the further fate of the trophoblast shell, and the transformation of the blood lacunae into the intervillous space, together with the formation of the secondary villi which goes hand in hand with this. The enlargement of the egg chamber is produced by two factors, both of which are already recognizable in the youngest ova. One is a dilation caused by the growtli of the ovum ; it finds expression in the curved course of the glands at the periphery of the egg chamber. The other factor is the splitting up of the marginal decidua, which shows itself even in the youngest ova in the growth of the margins of the opening of implantation over the ovnni. But this very splitting of the marginal decidua is a much disputed point in the history of placentation and is intelligible only by ascribing vital properties to the trophoblast. This continues to penetrate into the maternal tissues, opens vessels and glands, destroys portions of the glands entirely, and so divides them into a portion i>ertaining to thedecidua basalis and a portion pertaining to the capsularis. And since with the extension of the trophoblast the intervillous space also enlarges, the luraina of the glands open, at least temporarily, into the latter (Fig. 103) ; and, on the other hand, before their complete destruction, remnants of their epithelium are to be found in the wall of the space (Fig. 104). Since the destruction of the maternal tissue may be due in later stages to fermentative solution in addition to phagocytosis, the openings in the walls of the glands, for example, need not necessarily be filled up by penetrating masses of trophoblast, but the mere juxtaposition of such masses may be sufficient for the solution of tlie wall of the gland. Such a condition is shown indisputably, as it would seem, by Frassi, The "opening of glands into the intervillous space,*' as it was formerly described, has been regarded by a number of authors (Gottschalk, Hofmeier) as most certain, but by others it has been just as definitely denied; its occurrence has been advanced as evidence in support of the older theory of implantation, according to which the ovum adhered superficially to the mucous membrane and became surrounded by a wall formed from the membrane (deeidua "reflexa"). Frassi has been able several times to observe directly in serial sections the lateral openings of the glands and their free communication with the intervillous space which was thus effected (Fig. 103). Hofmeier had already described similar conditions. By these openjngs blood naturally passes from the intervillous space into the lumina of the glands and may greatly distend them, and thus the frequently repeated observation of greatly enlarged glands filled with blood in the neighborhood of the ovum becomes intelligible. The opening of the glands into the space is in any event a very transitory condition, since the trophoblast, blood-clots, and desquamation of the epith^elium soon close the openings and the glands are then completely divided. But one always finds beneath the ovum, in the deeidua basalis, large glands, usually filled with blood, which have lost their terminal portions. The blood which has filled them may in later stages serve as embryotrophe.

"As to the use of this term by other authors, see p. 130, note •• Analogous are the early stages in the development of the egg chamber in, for example, the guinea-pig (Graf Spee). " Concerning the use of this term see p. 151 et seq.

60. (Fro

Keibel Mall 104.jpg

Fig. 104. To the right, an epithelial remnant (Ep. R.), derived from a destroyed gland, and the lining layer (Al.) of the wall of the intervillous space. To the left glandular epithelium (Dr. E.). Between decidua (D,) with leucocytes (L.). x300. (From Frassi, 1908).

Epithelial remnants in the wall of the intervillous space (Fig. 104) have also been frequently observed (for example, by His) ; but they have usually been regarded as having been derived from the surface epithelium of the uterus and have been aCoepted as bearing on the implantation question in the same way as the **open gland communications." Frassi has also made clear the relations of these epithelia to the destroyed glands.

The decidua capsularis is completely closed in all ova older than that of Beneke. This closure must be effected by growth processes — either by the growth of tissue from the margins of the implantation opening, or by the organization of the basal portion of the closing coagulum, the protruding portion of this being thrown off. In the Frassi ovum, for example, the capsularis covers the entire ovum as a smooth, almost evenly thick layer. It still possesses uterine epithelium in its marginal portions and in patches even up to the upper pole, and glands occur at its margin ; their occurrence over the summit is impossible from the mode of development of the membrane. Fibrin, partly in streaks, occurs throughout the whole extent of the capsularis, and most distinctly at its summit ; but no trace of the implantation opening is visible in later stages. In the majority of ova in this stage of development there is at the summit a tissue rich in fibrin and poor in cells or even entirely without cells; this is Reichert's scar (for example, Hofmeier ; older ova of Leopold, Graf Spee, and Peters ; also Pfannenstiel, Rossi Doria, Cova, etc.). The scar either denotes the complete, organic closure of the capsularis, or, what is more probable, it is the first sign of what is later a complete degeneration of the capsularis, which becomes more and more stretched by the growing ovum, but is only very incompletely nourished on account of its possessing no blood-vessels of its own.

The changes in the trophohlast shell which occur during the first stages of development concern partly the arrangement of its cell materials, partly the cells themselves. By the ingrowth of connective tissue (chorionic mesoderm) into the trophoblast cords — a process which has already begun in the Peters ovum — these cords, which have previously been termed primary villi, become transformed into secondary villi, the true chorionic villi. These secondary villi are, therefore, preformed by the primary villi, but soon show independent growth.^^ The trophoblast, whose superficial layer is transformed into syncytium, becomes divided and spread out over the villi, until there remains only a single layer of distinct cells, over which is a layer of syncytium, also, as a rule, with a single row of nuclei. Both layers together constitute the epithelium of the villi. Very early the villi send out lateral branches and assume a dendritic appearance. The blood lacuna between them expand, unite together to a greater extent than formerly, and completely surround the villous growths; the lacunae thus become transformed into the intervillous space, which continues to extend toward the ovum until at length its mesoderm is covered only by a two-layered covering of epithelium. This covering and the mesoderm of the chorion now form the chorionic membrane or plate, which, as is characteristic for a placenta olliformis (p. 93), closes the intervillous space on the side towards the ovum.

    • The terms primary and secondary villi have been employed in the literature variously and with a somewhat different sense from that given them above. Marchand (1903) speaks of primary villi up to the tim'e of the penetration of the fetal blood into the mesodermal axes of the villi ; Hitschmann and Lindenthal (1902) and Pfannenstiel (1903), until the formation of the typical two-layered epithelium. according to Hitschmann and Lindenthal the primary villi are characterized by their power of active penetration.

But the entire tropboblast is not used in the covering of the villi. It also gives rise to the cell columns, the cell islands, and the basal ectoderm (the covering layer).

The cell columns (Fig. 105) are remains of the primary villi into which the mesoderm has not yet penetrated, and they unite the tips of the branches of the villi {the anchoring villi, in contrast to the ends of the lateral branches, which float freely in the intervillous space, the free or absorbing villi) with the wall of the intervillous space. They consist of cellular trophoblast with a superficial layer of syncytium or with the covering layer to be described later. At first they are of considerable length ; and since they contain no connective tissue the fixation of the ovum is at first a rather loose one, so that in an abortion or by the manipulation of a preparation young ova may comparatively readily be separated entire from the capsule (Fig. 106). It is principally from the cell columns that the activity of the trophoblast, the splitting up of the decidua, proceeds. Yet the cell columns continually diminish in length, the trophoblast is used up, and the mesodermic stroma of the villi extends out to the outer wall of the intervillous space. At the end of the second month the cell columns have vanished, the villi are firmly anchored, an abortion produces a separation of the decidua, and the splitting of the marginal decidua has ceased (Hitschmann and Lindenthal).

Keibel Mall 106.jpg

Fig. 106. — Aborted ovum from the beginning of the second month, expelled entire

The cell islands or cell nodes, also termed large-celled islands (Figs. 107 and 108), are also masses of trophoblast which have not been distributed over the villi (Langhans, Rossi Doria, Schickele, etc.). They are, it is true, attached to the ends of the villi, but otherwise lie free in the interWIlous space. The individual trophoblast cells are remarkable for their size and their swollen appearance, and have on these aCoounts been frequently taken for decidual cells; nevertheless, the occurrence of true decidual islands is at least doubtful,*^ The occurrence of vascular remains in the islands, which would determine their nature, has been described by Franque and Vassmer, but denied by Giese (1905), their supposed presence being based on an error of observation. The derivatives of the trophoblast, syncytium and "fibrin" (see pp. 151 et seq.), are of constant occurrence in the islands, which disappear in the course of the first months, being for the most part converted into "fibrin."

Keibel Mall 107.jpg

Fig. 107.— Section through the chorion of an aborted ovum of one month. (Greatest length of the embryo, 9 mm.) Chp., chorionic plate; Zi., Zi. 1., cell islands.

"The so-called decidual columns (Deciduabalken, Ijeopold) will be discussed later with the dei-idual pillars. Happe (1907), like Pfaunenstiel (1903) and Webster (1906), regards the islands as formed prineipaily of trophoblast, but also niaintaitis that they oontoiu decidual tlisue (more spindle-shaped eells, loosely connected together and partly with a finely granular intercellular substance).

The "basal ectoderm" is a term apphed by Langhans and his school to that portion of the trophoblast which occurs on the outer wall of the intervillous space; in somewhat older ova it there forms a stratified layer (Fig. 109) and is frequently retained until the end of pregnancy, if not as a continuous stratum, at least in masses of cells arranged in groups (Figs. 129-132). Its relations in younger stages, at the commencement of the formation of a continuous intervillous space, have been studied by Frassi. In such cases there is found upon the outer surface of the intervillous space the "covering layer," a simple layer of cells, resting as an almost continuous sheet upon the deeidua. "The nuclei of these elements are larger and take the stain more deeply and regularly (than the nuclei of the decidual cells). With strong magnification a distinct diflference can be perceived between the endonuclear substance of such cells and that of the decidual cells," The covering layer is everywhere one-layered in Frassi 's preparations; it is in places separated from the deeidua by fibrin and is lacking only in a few places. It occurs here and there between the cell columns or forms an external covering for these (Fig. 110), Transitions into deeidua are absolutely wanting, but, on the other hand, they occur into the syncytium, so that the covering layer is of fetal origin. The boundary between the fetal and the maternal elements is not always easy of determination; assistance is rendered in this connection, according to Frassi and Jung, by the leucocytes which occur abundantly and are always to be found in the neighborhood of the ovum. It would appear that they cannot pass beyond the boundary of the ovum, which penetrates like a parasite into the mucous membrane, and consequently they make possible the determination of that boundary.

The term transition zone indicates that the boundary is not a sharp one. Bonnet (1904), in the cases of older ova (those containing an embryo 3 mm. in length), preferred to speak of a detritus zone between the chorionic villi and the decidua. In association with it are symplasma formations of the decidual cells and enlarged glands and in the lumen exudations of secretion, blood, and leucocytes.

The intervillous space has also received different interpretations from different investigators. according to the older implantation theory, which held that the ovum became attached to the mucous membrane only superficially and that the uterine epithelium was retained, transformed into syncytium, the space was necessarily regarded as a portion of the cavity of the uterus enclosed between the ovum and the surface of the uterus; the occurrence of blood within it was only aCoidental, or, at most, a regular phenomenon only in later stages of development, its place being taken in young stages by a secretion of the mucous membrane, a kind of uterine milk. As a matter of fact the space was usually found to be empty in aborted ova (Fig. 107) and even in those obtained by operation and observed in situ (Fig. 118). These observations were taken as evidence opposed to a regulated circulation in the intervillous space; and the condition occurring in the Peters ovum, for instance, in which the lacunae were engorged with blood, was explained as the result of the action of the poison taken by the mother. Frassi, who also found the space empty in his ovum, although open communications with maternal bloodvessels could be determined at various places, rightly maintained, on the contrary, the existence of a regulated circulation, and pointed out that, after the inflow of blood had ceased as a result of the cessation of the heart-beats of the mother or of the ligation of the arteries during operation, an outflow of blood through the veins was still quite possible and, furthermore, would be aided by the final contractions of the uterine musculature. Such contractions, indeed, occurring as they do, though to a lesser degree, throughout the whole period of pregnancy, may form an important aCoessory factor in promoting a circulation, which at the best must be difficult and slow, through the very irregular space (Von Herff). The views of Pfannenstiel regarding the formation of the intervillous space will be considered later (p. 167). With the formation of the intervillous space and the gradual disappearance of the trophoblast shell the ovum passes from the embryotrophic into the haemotrophic phase of placentation.

IV. The Formation of the Placenta - Relations of the Embryonic Membranes up to their Maturity

(Hcemotrophic Phase of Placentation.)

a. Differentiation of the Chorion, Chorion Laeve, Decidua Parietalis and Capsularis

At first the trophoblast shell completely surrounds the ovum and villi are formed over the entire surface of the chorion; the entire chorion is at first a chorion frondosum. As the ovum increases in size and projects more and more beyond the general level of the mucous membrane, the decidua capsularis, which covers it and is only poorly supplied with nourishment, is gradually distended more and more, the circulation in the intervillous space over the convexity of the ovum becomes more and more difiBcult, and the villi on the surface directed toward the capsularis finally atrophy, so that the convexity of the chorion l3ecomes smooth, becomes a chorion Iceve, while the basal portion of the chorion frondosum becomes the placenta fetalis.

According to the observations of Pfannenstiel (1903) ova of the fourth week (from the cessation of menstruation) already distinctly show a bare spot at the capsularis pole, and even at the end of the second week this pole may be almost destitute of villi. Ova of the second to the fourth week project beyond the general level of the mucous membrane to very varying extents, either as far as the equator or even further. This condition is referred by Pfannenstiel to varying depths of implantation ; the shallower the implantation the more the ovum later projects beyond the level of the mucosa. The depth of the implantation, on its part, depends upon the intensity of the original growth of the trophoblast and its action on the maternal tissues. Concerning the relation which probably obtains between the depth of the implantation and certain abnormal forms of placenta (placenta marginata, reflexa, aCoreta) see Grosser 's **Lehrbuch." The further fate of the chorion Iseve will be considered in connection with that of the decidua capsularis.

The decidua parietalis (vera), in accordance with its premenstrual relations, is alreadv more or less distinctlv diflferentiated into a pars compacta and a pars spongiosa at the time of implantation.^^ The former is essentially the region of stroma changes while the latter shows characteristic gland forms. But both layers during the first weeks of pregnancy still present the premenstrual type, in accordance with the inhibitory effect exercised by the implanted ovum upon the changes of the mucous membrane (p. 119) ; in the stages now under consideration (Fig. Ill) they are differentiated.

    • Peters did not observe the compact layer and believed that it develops later, and Siegenbeek notes the lack of a distinct boundary between the two ; nevertheless it must be remembered that in this respect variations occur also in the premenstrual mucous membrane. In the Jung ovum the layers are separated.

The deeidua eompacta (Fig. 112), in addition to the straighter terminal portions of the glands and greatly enlarged blood-vessels, alsocontains decidual cells, which are formed from stroma cells by the continuation of the changes that are characteristic of the end of the premenstrual stage. They are large, clear, vesicular cells, as much as 50 n in diameter, and are round or, from mutual pressure, polygonal, resembling epithelial or epithelioid cells. The changes by which they are produced do not occur simultaneously in all the stroma cells; and even at the height of the formation of the deeidua one may find here and there stroma cells but slightly altered and showing division and growth phenomena, so that Marchand (1904) recognizes two types of decidual cells, large and small. The mature (large) decidual cells show, at the most, only direct nuclear division (they contain frequently two nuclei and indications of a cell boundary between the nuclei) and, as fully differentiated cells, are capable of no further progressive or n^gresaive development, ilany of them degenerate during the second half of pregnancy and are disposed of by leucocytes; but the majority are thrown off either during or after birth. After the fourth month they all become smaller again and more spindle shaped and are arranged parallel to the surface (Pfannenstiel). according to Wederhake (1906), Unna plasma-cells also occur in the decidua, and transitions between these and typical decidual cells.

!.— DeUJI of Fig, III; the gi»ail duct tht.t iodinted by Dr.l.ia the decidum pBrieOlia , 9 Kcond month. The (land contatos mcretioo and sroiuid il an typical decidual oells and a few IsucocyMm. a 350.

The significance of the formation of the decidual cells lies, according to Marchand, in the storing up of glycogen;*" the majority of other authors see in their formation a provision against the too intensive penetration of the ovum into the mucous membrane, without furnishing suflBcient evidence for such a view. according to Marchand, spindle-shaped epithelial cells grow out as wandering epithelial cells from the degenerating glands of the compaeta into the stroma and may there fuse to form multinucleated masses.

"Drieasen (1007), who recently hafi aprain taken wp the older observations of Lan^hflns on tlie oeeiiTTence of jrlycoeen in the <1eeidua, finds that substance chiefly in tlie fflandiilar epithelium of the aponpirma ; it is not always recopnizable in the decidual cells. In the second half of pregnonoy it sradiially disappears.

In the deeidua spongiosa are to he found at first the glands of pregnancy, also characterized by the further development of the premenstrual changes (Figs. 87 and 113), They are greatly enlarged and tortuous, irregular in section, and filled with secretion. The enlarged epithelium projects into the lumen in the form of papillae borne upon small elevations of the stroma; it is composed of high cylindrical cells, with clear marginal zones filled with secretion. Between the glands are very small connectivetissue septa with scattered decidual cells; only near the larger vessels are the septa broader. After the second month the epithelial papillse disappear and the cavities of the glands become low and broad as a result of the stretching of Uie entire deeidua, due to the increase in size of the uterus. The epithelial cells continue to grow broader and lower (Fig, 114) until, finally, they resemble an endothelium and are lacking in places. The cavities of the glands then appear as small, elongated clefts, with thin inter\'ening walls, resembling in mass an empty venous plexus


Keibel Mall 114.jpg

, 114. — ^The«8g membranw And uterine wall opposite the ptaoenta in the fourth moni i9eagFig.130. (Embryr, 13'^ctn.iD vertex-bnechmeaaurenieiit.) .4..iunaion; CA.-S., c I tissue; CA.-Z., degenerated rhorionic villi; Cimp., deciilu* psrietsliH campoctaand ca

Fig. lis.— Detail of Fig. 114. The dtgenerated villi of tlie rhoiioo Iseve in the fourth month (the lionic epitlielium; Ck.-B., cliorionic cuunective liuuei Drc., decidua CBpsularia and parietalis compacts, Kith leueooyte?. X 300. (Fig. 117). The separation of the decidua in an abortion or at birth can therefore take place easily in the apongiosa. Only the deepest portions of the glands (the boundary layer of His), which lie between the irregularities of the surface of the muscularis, retain their cubical epithelium and form the starting point for the post-partum regeneration of the mucous membrane.


The surface epithelium becomes flattened and loses its cilia (according to Marchand) ; furthermore, fat globules are formed in the cells and symplasmic formations occur, and toward the end of the tliird month the epithelium has practically disappeared. At the same time the cavity of the uterus, the perional space (the space surrounding the ovum (v,<i;) : Webster), which has at thi.s time only a potential existence, disappears as the capsularis comes

t»IieoUBly. Amn.. Bmnion; Ch.-B., chorionic connective lifsiw: Zic., itilermertiste Kme (chorionic epitlilium, remMngof the villi, dec id ua capiularis, and decidus parietalia compaoU); D. ip.. decidim parielaii* ponsiOAa; Dr., glandular r^raais. into contact with the parietalis. The capsularis (Figs. 114 to 117), by stretching and by degeneration as well, has become greatly reduced and its remains now fuse with the decidua parietalis. The view that it remains recognizable as a streak of cells up to the close of jjregnancy is probabljbased on an error, the chorionic epithelium being mistaken for it. The degeneration of the capsuiaris can be demonstrated beyond question in the region of the internal os uteri, where its fusion with the decidua parietalis is impossible. Even at the fourth month the eapsularis (Fig. 116) consists in that region of only a very thin layer of flattened elements with some elongated clefts, probably remnants of the intervillous space. The chorion Iceve also shows extensive degenerative changes. The epithelium of the villi disappears, their stroma undergoes hyaline degeneration (Figs. 114 to 116), and between the hyaline masses so formed one finds the detritus of cells and leucocytes. At the summit of the ovum even these hyaline remains of the villi vanish (Fig. 117), but they persist in the neighborhood of the placenta. The epithelium of the chorionic membrane itself is, however, usually recognizable in the mature egg membranes; external to it is a zone of detritus with the remains of the villi, the eapsularis, and the decidua parietalis compacta, in which also hyaline degeneration, as well as fusion and destruction of the cells, has occurred (Fig. 117). Still more externally are the remains of the spongiosa, which at the close of pregnancy is reduced to a thickness of 1-2 mm., but which still contains remains of the gland cavities. The fatty degeneration of the decidua parietalis, which was formerly regarded as the rule, occurs at most only in exceptional instances.

b. The Placenta

In the formation of the placenta the chorion frondosum and the decidua basalis participate, the former constituting the placenta fetalis and the latter the placenta materna.** The placenta fetalis consists of the chorion plate and the chorionic villi; both contain a mesodermal stroma 'and an ectodermal (trophoblastic) epithelimn. The stroma of the villi is at an early period distinctly fibrillar and provided with fusiform cells in the principal stems and in the chorion plate ; in the lateral branches it is at first formed of stellate cells with wide intercellular spaces, but even in these portions it soon assumes a fibrillar character. In the meshwork of the connective tissue there frequently occur in young ova lymphocyte-like structures and some especially large cells, with highly vacuolated plasma and large nuclei (Fig. 119), to which Hofbauer has called attention and which he brings into relation with the plasma cells. Their significance is, however, still uncertain. The capillaries of the fetal vascular system lie, for the most part, near the surface of the villi. according to Bonnet (1903) lymph-vessels also occur in the stroma of the villi and can be followed to larger vessels in the chorionic membrane. Nerves are not recognizable in the placenta (Bueura). Fossati has described a network of fibres, characterized by special histological peculiarities, as occurring around the chorionic vessels. In the stroma of the chorion plate Vol. I.— 10

    • This latter term has varied somewhat in its sigificance. Kolliker terms the entire basalis the placenta materna and divides it into a pars non cadnca seu fixoy which corresponds to the spongry portion, and a pars caduca, which is expelled at birth and is usually known as the basal plate. However, the latter alone is frequently termed the placenta materna.

Keibel Mall 118.jpg

Fig. 118. — Anlage of theplaoenta from the second month. From a uterus obtained The embryo had a verl«x-breech length of 28 mm. The same ea« as ii shown in Figs, lli, im. ana lao. rti.-P.. chorion plate; Or., glands: b.£.. ba-'al ectoderm; i/f.. anchorins villi; M., miUKnilarisuteri: m.A., maternal artety in a placental Mptum (decidual pillart; N. F., Nilabuch's fibrin slria; «. F.. Rohr's fibrin -atria; Z.-J„ cell island. X IS.

Keibel Mall 119.jpg

Fig. 119.

Langhans has described a more superficial subchorial vascular layer and a deeper fibrillar one, which shows no sharply defined boundary from the Coelom. These layers become distinguishable only at about the third month. Glycogen is found in young ova chiefly in the connective tissue of the chorion plate and of the larger villi {Happe, Driessen). (For further particulars concerning the stroma of the villi see Happe, 1907; and regarding elastic fibres consult Fuss, 1906.)

The form of the villi, which is determined largely by the stroma, changes during pregnancy in that, on the one hand, the branchings of the villi become continually more numerous and the villous trees larger, and, on the other hand, the branches themselves become more slender and longer {Fig. 120); yet even in the mature placenta variations in this respect occur. In each villus one or two arteries occur and one or two somewhat stronger veins, the two sets of vessels being connected by a capillary network lying immediately beneath the epithelium (Fig. 121). (Concerning the form of the villi see Minot, 1889, and Happe, 1907.) The chorionic epithelium, as has already been stated, is twolayered after the formation of the villi (Fig. 129). The deeper layer, which is composed of distinctly separated cells, is usually named from its discoverer the Langhans layer, but is also termed the cell layer. The superficial layer is termed simply syncytium or also syncytial layer or covering layer.^^ The two layers together form the diplotrophoblast of Hubrecht. As a rule, the cells of the Langhans layer are arranged in contact with each other in an epithelial manner, but frequently the syncytium extends between the cells (Fig. 119) to the basement membrane of the epithelium (Bonnet, 1903). As a result of this it appears in places as if the cells were arranged in separate cell territories enclosed in a ground substance and with a kind of capsule or bounding layer. This condition is regarded as the rule by Happe (1907) among recent authors. The syncytium generally forms a layer of almost the same thickness as the cell layer and has but a single layer of nuclei. Vacuoles, that are so striking in the syncytium in early stages, are also to be seen at later periods and may be the expression of degeneration or of the absorption of material. On its outer surface it is provided with a delicate membrane, which proves to be composed of prickle processes, stiff hairs or rodlets, stereocilia (Graf Spee, Von Lenhossek, Bonnet). This membrane is perhaps existent only under certain functional conditions and cannot always be perceived ; the rudimentary basal bodies described by Lenhossek as occurring in the cilia have not been found again by Bonnet. Indications of absorption in the form of fat globules, basophile granules, and mitochondria occur in the syncytium, and it takes up haemoglobin in a soluble form. On its outer surface it frequently bears irregular, multinuclear elevations or buds (proliferation nodes; Fig. 122), which occasionally become separated and may be carried in the circulation far from the intervillous space (the deportation of syncytial elements of Veit). They are probably indications of amoeboid activit)^ which, in all probability, occurs in the syncytium.*^ Degeneration (the formation of symplasma syncytiale with spiny nuclei and the dissolving of the plasma into clouds or drops) may be observed, according to Bonnet, in the syncytium in younger stages; in older stages it takes on other forms (see p. 151).

  • To the two layers of chorionic epithelium have been ascribed by different investigators very various and somewhat remarkable significances. For a review of the different origins suggested for the epithelium, which have been copied in a number of papers, see Waldeyer, 1890.
    • Also entire villi may be torn away by the blood stream and enter the maternal vascular system.

Glycogen occurs in the cytotrophoblast (in the cell columns and cell islands, less regularly in the Langhans cells) ; it is lacking in the syncytium. It disappears completely with increasmg maturity of the placenta (Driessen, Happe, 1907).

Mitoses occur only in the Langhans layer; in the syncytium only direct division occurs, and it is rare (Van Cauwenberghe). The direct passage of a cell from one layer into the other has not yet been observetl in older stages and occurs only occasionally in younger ones (see p. 114). Nevertheless, the distribution of the nuclear divisions must be taken as evidence that even in later stages the cell layer is the source of the syncytium and adds to it. The older opinion of Kastschenko, which has recently been revived by Happe (1907), to the effect that the cell layer arises from the syncytium, seeina to be overthrown by this. Between the syncytium and the cell layer there is, according to Graf Spee and Van Cauwenberghe, frequently but not regularly a cuticula or deep syncytial membrane, which, however, is believed by most other authors to be an artefact ; beneath the cell layer is a basement or hyaline membrane. (For details concerning the epithelium of the villi see Marchand, Friolet, Van Cauwenberghe, Happe.)

In addition to the occurrence of proliferation nodes there is also another phenomenon that speaks in favor of amoeboid activities in the syncytium; this is the relation of the haftal (serotinal) or syncytial giant cells (Figs. 123 and 124). In the decidua basalis one finds even in young stages multinucleated masses of protoplasm which cannot be distinguished histologically from syncytium and are of great importance in connection with the significance of the syncytium. In the Frassi ovum tliey are throughout {except at one doubtful spot) in connection with the syncytium of the villi, but in the preparations of J^eneke, Pfannenstiel, and Friolet, for example, free masses of syncytium occur in the decidua basalis — indeed, even in the superficial layers of the muscularis and frequently in the neighborhood of vascular endothelium. They are most frequent at about the middle of pregnancy, when they may reach a very considerable size (Fig. 123) and may penetrate far into the muscularis (Fig. 124); nevertheless their abundance is subject to rather great individual variations. Toward the end of pregnancy they diminish in number. Pfannenstiel finds support, in their oCoasional topographic relations to the vascular endothelium, for the derivation of the entire syncytium from the endothelium; but syncytial growths arising from endothelia are denied by I'Molet and Frassi. Friolet leaves the possibility of their origin from the connective tissue an open question; Pels Leusden, Webster, Frassi, and others regard them as derivatives of the (fetal) syncytium, that penetrate individually into the maternal tissues,* and this view is certainly the most probable. The fact, also, that they degenerate post partum, without taking any part in the regeneration of the mucous membrane, is in favor of this view (Wormaer).

Keibel Mall 122.jpg

Fig. 122.— From matun

Keibel Mall 123.jpg

Fig. 123.— Giant cells ber

" That they may also penetrate toward tlie centre of the ovum is indirsted at present only by the very definite statement of Beneke (p. 115). Sie^ibeek also records the remarkable occurrence of a syncytium ma5is between the chorionic epithelium and connective tissue, but considers it to have occurred by active immigration into the o\Titn through a tear in its wall, which he assumes to have occurred during life.

Keibel Mall 124.jpg

Fig. 124. PlMenU tn lilu from the second half of pregnanoy. with numerom BUbplftomUl Byncytinl gifiDt »Ub. D.b., dfciduB ba»»Lis; Dr., (Isads; Get,, msternal vea«ls; Hi., unchoring villi; MiMC., mu» Even in the fourth month the cell layer is present only in patches, the syncytium resting, for the most part, directly on the stroma of the villi. Toward the end of pregnancy individual Langhans cells are still to be found beneath the syncytium, according to Van Canwenberghe, yet this is certainly a by no means frequent occurrence. The layer is partly spread out and stretched over a constantly increasing area by the growth of the villi and is partly used up in the formation of syncytium {Fig. 122). The syncytium also frequently shows signs of degeneration ; it becomes greatly attenuated and may even be wanting at many places on the surface of the villi. In such cases so-ealled placental fibrin occurs on the villi. This "fibrin" has also frequently been the object of investigation and of controversy. In quite young ova (Peters, Leopold) it does not occur; in older ones, in which the intervillous space has formed, it first appears usually aa a stria situated some distance from the space in the basalis or even in the capsularis. Chp.

Fig. I25. Chorion plate with aubehorisl eloai plBcenM. Chp.. chorion piatfl; k. F., nnaliied fibrin; DColive-UHue Btronu at desenerating villi, x SOl

The time of its appearance does not seem to be constant (see p. 127) ; but having once appeared it persists until the close of pregnancy. It was first described in a dissertation written by one of Langhans' pupils and was named, from the authoress of the paper, Nitabuch's fibrin stria. A second stria also occurs, though not constantly, immediately in the wall of the intervillous space and has been termed Rohr's stria*^ (Fig. 118). In addition, there is a third stria which is constant in its occurrence close beneath the chorion plate ; it appears, however, later, only in the second half of pregnancy, and is known as Langhans' stria. In the same region is to be found especially the "canalized fibrin" of Langhans (Fig. 125), and, finally, quantities of fibrin occur everywhere in the mature placenta and between the villi ; these fibrin masses are, for the most part, microscopic in size, but frequently increase to extensive structures. The small ones are termed fibrin nodes, and the larger are known as white infarcts. The latter may occasionally form almost half the mass of the placenta.

Langhans and his pupils regard the Nitabuch stria as marking the boundary between the maternal and fetal tissues. It is certainthat it occurs in the transition zone and that the maternal tissues that may be between it and the ovum quickly degenerate. Jung derives the stria from the boundary zone of the maternal tissue (see p. 115). It is at all events basal to tj^pical decidual tissues, and is between the ovum and the basal ectoderm and degenerating tissue, whose origin cannot always be certainly ascertained. It is traversed by maternal (uteroplacental) vessels. That it is practically the boundary between the mother and the ovum is also shown by its relations to the leucocytes; these, as* a rule, do not pass beyond the stria. The fibrin of the Nitabuch stria is apparently the first to appear in the placenta, yet the methods for detecting the material in other portions of the placenta are insufficient. In general this so-called fibrin is by no means typical blood-fibrin, it shows only occasionally the histological reactions of fibrin. Hitschmann and Lindenthal believe that the fibrin reaction is shown only at the commencement of its formation, and that it later alters with age. It would be better, therefore, to designate the substance by some indifferent term, such as fibrinoid or fibrinoid substance. At all events, the stimulus for the formation of fibrinoid is afforded by degenerative changes, those occurring in the decidua and chiefly in the region of the basalis being responsible for the formation of the Nitabuch stria and the smaller basal fibrin masses; yet the amount of participation of the individual tissues of that region cannot as yet be strictly defined. At other places the trophoblast must be regarded as the seat of the fibrin formation; for very large quantities of fibrin are found at places where the decidua is wanting, as, for instance, beneath the chorion and between the villi. The maternal blood may also participate, forming true fibrin; examples of this are shown in places where the fibrin contains red and white blood-corpuscles. It is also possible that the blood fibrin may become so altered in course of time that it can no longer be detected by the usual histochemical methods. It may be such fibrin that occurs' in the decidua basalis and in the white infarcts, deposited as the result of the disturbances in the circulation produced by the degeneration of the epithelium of the villi and the fusion of these structures, or as a result of the imperfect outflow of blood from the intervillous space produced by villi being carried into the maternal veins, as Giese suggests. The subchorial ** canalized fibrin" also presents a peculiar layered structure (Fig. 125), which may be explained as the result of the deposition of suCoessive layers of blood fibrin, especially since the blood stream is undoubtedly greatly retarded in the roof of the intervillous space.

" Rohr himself names this the tipper stria, terming Nitabuch's the lower ttria.

A small fibrin node b

The derivation of fibrinoid from the trophoblast is based upon the study of the formation of fibrin nodes on the villi; and it is also supported by what can be seen in the formation of the Langhans stria. In the villi one finds the first stages of fibrinoid formation partly between the syncytium and the connective-tissue stroma, partly where the epithelium of the villi has almost disappeared, as it does in every mature placenta. The occurrence of the fibrinoid between the syncytium and the stroma points to the cell layer as the seat of its formation, and this indication becomes stronger in regions where the villi are closely packed together at the time when the fibrin formation begins. One can then observe how the formed masses of fibrin produce a cohesion of the villi and how the Langhans cells occur between the fibrinoid and the stroma of the villi ; also in the mature placenta the Langhans cells, practically wanting elsewhere, may be seen at the surface of the villi (Fig. 127), usually in a continuous and sometimes in a double row; and, furthermore, these cells occur free in the formed fibrinoid, where they become vesicular in appearance and gradually lose their staining properties, persisting for some time as "ghosts" of their former selves and eventually becoming completely converted into fibrinoid. The process of conversion cannot be termed a direct necrosis of the cells; it has great similarity to what is seen in the formation of the matrix of many kinds of connective tissue, as, for instance, when cells and even whole cell territories become transformed into matrix in some kinds of cartilage. It is a process apparently intermediate between secretion and the direct transformation of the peripheral portions of the cells, and by the continuation of it the entire cell becomes transformed. The fibrinoid so formed lacks the property that inhibits coagulation and that is possessed by the living epithelium of the villi, and so the mass of the fibrin node is increased by the formation of fibrin from the blood. Whether the syncytium also takes a direct part in the formation of fibrinoid, or degenerates, or, perhaps, first divides into separate cells which are then transformed into fibrinoid, has not yet been determined. The degenerating stroma of the villi later undergoes a very similar (hyaline) transformation and disappears in fibrinoid.

The chorion plate is the seat of formation of the Langhans fibrin stria. In it even in the fourth month a partial transformation of the epithelium into fibrinoid can be detected, and in the sixth month the epithelium in the middle of the placenta is replaced by the fibrin stria. The lack of epithelium, on the one hand, and the retarded blood flow, on the other, then produce blood coagulation in layers, the result being canalized fibrin.

An important source of fibrinoid is to be found in the cell islands, that are so frequent in the first month and later disappear. In these also the beginning transformation into fibrinoid is evident very early (Fig. 108). Possibly these trophoblast masses give a stimulus for the formation of the larger fibrin masses.

  • Langhans spoke of the canalized fibrin as a tissue; but this conception of it is incorrect, since it cannot be considered as living material.

The description of fibrin formation given above resembles closely that given by Schickele. The derivation of the fibrin from the trophoblast, in part at least, has also been maintained, among others, by Kermauner, Hitschmann and Lindenthal, and Giese. These authors advocate even more strongly than has been done above the occurrence of disturbances in the circulation and the formation of fibrin from the blood. Steffeck (1890) has derived all the fibrin from proliferated decidua, a view that is to-day untenable; he has apparently throughout mistaken the swollen degenerating trophoblast cells for decidua cells. The transformation of the trophoblast may, however, be carried even further and produce a liquefaction of the formed fibrin; thus arise the placental cysts which are of very frequent occurrence in mature placentae. Superficially situated cysts, occurring in the Langhans stria, may reach the size of a hazel-nut or even larger; more frequently are small microscopic cysts in the middle of the tissues (Fig. 128). They are always enclosed within a mantle of fibrinoid containing degenerating trophoblast cells and are frequently lined by a flattened, endothelium-like layer of these cells (Giese).

The white infarcts form, as the result of a combination of fibrinoid and blood-fibrin formations, larger solid masses, which may enclose large villi, causing the degeneration and death of their connective tissue, which eventually becomes imrecognizable as such. The destruction of the connective tissue and chorionic vessels in the infarct is, however, a secondary process, and not primary, as Ackermann supposed, since the villi are nourished from the intervillous space and not by the chorionic vessels (see p. 164). Eed infarcts, which are of much rarer occurrence and owe their name to their color, are due to mass coagulation of the blood in the intervillous space.

It is generally supposed that the cytotrophoblast, with the exception of some scattered Langhans ceils lying beneath the syncytium of the villi, has entirely disappeared in the mature placenta; in speaking of the formation of fibrinoid, however, attention has been called to the occurrence of isolated trophoblast cells, and they are to be found rather constantly in two other situations: in the floor of the intervillous space, their occurrence in this region will be discussed in connection with the description of the decidua basalis ; and in the region of the subchorial closing ring (Waldeyer). In this region they form a cell plate of varying breadth, circular, in correspondence to the margin of the placenta, and often wanting; when present, however, it lies between the chorionic connective tissue and the Langhans fibrin stria, extends inwards from the margin for about 1-2 cm. and laterally passes over insensibly into the epithelial layer (p. 143} which persists on the outer surface of the chorion laeve {Fig. 125). The closing ring is the remains of the epithelium of the chorion plate, which further

Bp., bkjnl pLa-e: Chb.. Cht., chorionic connective tiuue sdiI epithdium belonsing (o tbe chorion iKve; Chp.. chorion plalc; D. p., cjeciilua pariolalin (and capsuliris); Fib,, libria: I. G,. m. G., fetaJ and matenul vesKle; /„ inFsTct: K., calareous deposit: ii. R.. iDlerviUoiu epux: f. Hr.. subchorisl cloMng nag. frequently iaterrupleil: b. Tr., remejus of bual Irophoblaat: Z. I., villiu which travsrsei the Bubchm-inl cloddA Hng^ 2i..coDnective-ti»ue stroma of viUi. K 17. in has completely disappeared, that is to say, has become completely transformed into fibrinoid, and at the margin of the placenta has, it is true, lost its syncytium and has formed fibrinoid, but yet has largely persisted or has even become many-layered as the result of proliferation. In these cells, even in the mature placenta, the transformation into fibrinoid can be observed, and the cell plate is usuallj' not continuous, but shows local defects (Fig. 129).

Winkler originally described a continuous plate of cells as existing beneath the connective tissue of the chorion plate, naming it the closing plate and deriving it from the decidua. Kblliker pointed out that a complete plate does not exist and speaks of a decidua subchorialis occurring at the margin of the placenta, and by this name the tissue is now generally known. Pfannenstiel endeavors to explain it as produced by an undermining of the marginal decidua by the marginal villi. The idea of a decidual origin for the layer is based upon the pale and swollen appearance of the cells, but this, as has already been several times noted, is not a proof of its origin. Langhans in 1877 expressed doubts as to the decidual nature of the layer and later (1891) decided in favor of an ectodermal origin; Hitschmann and Lindenthal agree with him in this. In the mature placenta the closing ring is occasionally broken through by villi (Fig. 129), which are usually atrophic and belong to the portion of the chorion which is transitional between the chorion frondosum of the placenta and tiie chorion Ifeve, and this fact is sufficient in itself to overthrow the idea that one has to deal with an undermined marginal decidua. There remains, therefore, for consideration only the assumption of an active growth on the part of the decidua cells of the placental margin towards the middle of the placenta, a supposition which has little probability on account of what has already been said as to the degeneration of the decidua in the later stages of pregnancy. But in addition this possibility is also excluded by the study of the margin of the placenta in different months of pregnancy. This shows {cf. Fig. 130) that the transition of the placenta into the chorion laeve during the progress of pregnancy is a gradual one and the two structures are first sharply marked out towards the end of it. Normally a proliferation of the marginal decidua or an undermining of it is never to be seen; but, on the other hand, such preparations directly show the gradual degeneration of the epithelium of the chorion plate in the middle of the placenta and its transformation into the subchorial closing ring at its margin.

Keibel Mall 130.jpg

Fig. 130.— Margin of a placenta of the fourth month (vertex-brewh length of the embryo 13^^ cm.). A decidua :<ubeboTiaLiB ip wanting. The glantt eavitieH of the ppongtosa (Dr.) liave been separalAl in the preparation. Am.^ amnion; Ch.. choHon; b. E.. btuwd Qcloderm; 6. E. tF.). batiaJ eetodenn in procesa □t traruifonnatiOD into Bbrinoid; Fib., fibrinoid; Mute., musculBriv; h: R., inlervilJouB i-pace; Zt., ceU nodes. X IS.

    • Sfameni takes a different view of the origin of the placenta marginata. He refers it to a lack or insufficiency of pressure within the ovum and to insufficient stretching of the wall of the uterus. Compare also Kromer (1907) and Liepmann (1906), as well as the polemic of these authors in Centralbl. f. Gynak., vol. xxxii, 1908.

Perhaps a portion of this epithelium may persist throughout the entire extent of the placenta, just as it does at its margin ; at least this would explain cases such as that described by Steffeck, in which an actually complete subchorial epithelial plate is said to have been present, and which was identified by that author as decidua. The conditions in a placenta marginata are quite different, for this may well owe its origin to an actual undermining of the marginal decidua {cf. Pfannenstiel, 1903, and Grosser, *'Lehrbuch'^).«^ The decidua hdsalis {placenta materna) is divisible in later stages of pregnancy into a compact layer, the hasal plate of the placenta, and a spongy layer. The former, which closes the intervillous space on the basal side, is formed from the portion of the premenstrual compacta that is not destroyed by the ovum during implantation; the latter is formed from the premenstrual spongiosa. This shows (Figs. 118 and 124), in general, the same changes as the decidua parietalis spongiosa; only the layer is thinner, and the gland spaces appear to be less frequent, perhaps because some of the glands, which in the early stages of the development were filled with blood, have degenerated; between the glands are the sjnicytial giant cells already mentioned. The basal plate (Figs. 131 and 132) consists of decidua, which toward the end of pregnancy again contains more fusiform cells, and also of the fibrin stria* already described and of the remains of trophoblast derived from the basal ectoderm and the cell columns of the anchoring villi. These trophoblast remains, again, are partly syncytial in character and partly appear as large, swollen, mononuclear cells (mononuclear giant cells) similar to those found in the early stages of fibrinoid formation in other places; these cells lie, sometimes singly and sometimes in groups, in degenerating tissue and in later stages may extend peripherally beyond the Nitabuch stria. The trophoblast masses are no longer, however, in direct connection with the anchoring villi ; the tips of the latter usually dip into masses of fibrinoid, which extend to the stroma of the villi. Frequently this is more or less degenerated, as it is in the infarcts.

In the basal plate there also occur the so-called choriodeddual vessels (Euge). They are relatively large stems, visible to the naked eye in the expelled placenta, provided that they are well filled with blood, or, better, injected from the vessels of the villi ; they pass out from the villi, and either terminate in the basal plate or enter the stem of a villus ascending from the basal plate. This fact indicates that the villi concerned have come into contact with the basal plate and have lost their epithelium and stroma by degeneration, while their vessels have persisted and have become enlarged by the blood-pressure, partly on account of degeneration in their walls. Usually remains of trophoblast and of the stroma of villi (Fig. 133) are to be found in the neighborhood of the vessels, provided their entire surroundings have not been transformed into a fibrinoid mass.

Keibel Mall 132.jpg

Fig. 132. — Basal plate of mature expelled placenta. Am.-ji.. arteria uUraplacea talis ; Db, decidua baulis : Ep.. epithelial remaiiu in (be Qoor of tbt intervilloua Bpsw; Fib., fibrin; Hi., ancboring villua: N. F>.. the Niubueh fibrin atria; Ri., monoDualeai liant cells (remains of tiophobUtill; Z>.. connective-tissue stroma ot villi endosed by fibrin. X TO.


Kuge believed that his discovery of these vessels indicated a vascularization of the decidua, that is, of maternal tissues, by fetal vessels; the explanation' given above has already been advocated by W. Wolska, working under Langhans' directions, and has been confirmed by other authors. The statement, which has appeared in some articles, to the effect that Huge has described an anastomosis of fetal and maternal vessels, is erroneous. From the basal plate there extend towards the intervillous space the decidual pillars, which represent the septa placentiB of later stages. The decidual pillars (Fig. 118) are to be regarded as portions of the decidua basalis compacta which have been spared during the penetration of the trophoblast. In structure they resemble the basal plate. As regards their number and arrangement in young stages adequate investigations are as yet lacking. occasionally, but certainly not frequently, the pillars seem to project for a considerable distance into the intervillous space, even to near the chorion plate, and, in sections, appear to have no connection with the basal plate, so that they seem to be "deeidua islands" or decidual trabeculce (Leopold). (That free decidua islands do not, in all probability, occur has already been noted.) The septa placenfce in later stages and at the close of pregnancy divide the placenta into separate lobes or cotyledons, which do not,

however, represent closed areas, since the septa in the middle of the placenta are very low and even at the margin reach the chorion plate only in small part. The original formation of these septa from deeidua cells is almost always very difficult of determination in the mature placenta (Fig. 134). The decidua cells have, for the most part, degenerated and disappeared, and in their place there remains only an empty mesh-work, into which the trophoblastic anchoring villi penetrate. These frequently grow completely through the septa, so that again fibrinoid formation and also the inclusion of neighboring villi, together with their stroma, may be found in the septa. Many septa at the close of pregnancy seem to be composed entirely of fetal elements.

The basal plate is traversed by maternal or uteroplacental vessels, destined for the intervillous space. Arteries and veins pass through the plate in sinuous courses, but at their entrance into it they lose their muscularis and are represented by channels lined only by endothelium. And even this is usually lost when the vessels pass through the fibrin layers of the plate. The arteries generally open in the region of the septa or close beside them, while the veins arise rather towards the middle of the cotyledons. This arrangement favors, to a certain extent, the intervillous circulation. Both arteries and veins, as a rule, traverse the wall of the intervillous space obliquely, yet villi are frequently sucked into the veins or they may, as has already been mentioned, be torn away and, passing into the veins, close them, thus producing disturbances in the circulation.

Keibel Mall 134.jpg

Fig. 134. — Saptum of » nutun eipdled pIsMnta. Tr,. trophoUut; Z., stroma of rilliu that hu foaed with the Kptum. xao.


" The opinion of Waldeyer that the endotbelium is continued for some distance upon the wall of the intervillous space, though in accordance with the older views, has not been confirmed by later investigators.

— Marginal portion of a mature expelled placenta vritli ' distendKl wilh ur. Ch.l,, chorion leve; D., trsgmenU of decidiu; up. (/.. uteroplaCoDlaJ vesselt; K., flUperficial calcareoua depoHit; 0, opening into theroAricinalBiriuH (a tear, produced at birth by the divi^on of A uterine vein), villi, which project into the margiaal sinua. beinc seen through the opening; Rt,^ Tbe conditions of the circulation in the placenta are quite peculiar and are found nowhere else in llie body. The arteries open into a wide, very irregular space, extending throughout tbe entire placenta and limited only by fetal elements (and by flbrinoid). The space is formed from trophoblast laeunte and is filled with blood by the erosion of maternal vessels; these at first are of merely capillary size or but little greater. With the increasing importance of these afferent and efferent veeeels they become graduaJly larger. Originally the opening of the vessels occurs in the region of the transition zone, and even later the union of the vessels with the intervillous space is still characterized by the fact that their endothelium has no continuity with any of the cellular elements that line the space (syncytium, basal ectoderm). The intervillous space is both the functional and the nutritive vascular space of the placenta; from it the villi derii'e their nourishment, the fetal circulation playing merely a subordinate role in this respect. Even after the death of the embryo the placenta may persist for a considerable time and may continue to grow, although only in an atypical n

One of the efferent channels of the placenta is the marginal sinus, Meckel's blood-channel, the sinus drcularis; it is situated in the anj^le between the margin of the placenta and the chorion laevc

++++++++++++++++++++++++++ Fig. 13a.— M»r«in of the plaamU i

++++++++++++++++++++++++++ (Fig. 135), and does not encircle the entire placenta (it is wanting at the region shown in Fig. 129), but only about one-quarter, or at most seven-eighths, of the circumference (Budde) ; occasionally it can scarcely be recognized. It is not to be regarded as a continuous, regular vessel, but as a rather irregular apace of varying diameter, which presents peripherally gaps and openings, corresponding to uterine veins that have been torn away; and gaps of varying size also occur on its inner wall through which bunches of villi project and by which it is in communication with the intervillous space {Figs. 135 and 137). Budde agrees with earlier

Keibel Mall 137.jpg

Fig. 137.— Mursinal siaiu of K mstun eipeUed pluenta with sn sDdothelium-like lipiDi. Ch. I., Chorion ++++++++++++++++++++++++++

authors in regarding the entire sinus as the marginal portion of the intervillous space, its inner wall, so far as it is formed, being produced by cohesion of the marginal villi and by the formation of fibrin. This explanation does not seem to suffice for all cases; in younger ova greatly enlarged veins occur, which have a circular course and have been regarded as the marginal sinus {e.g., by Friolet and in the case shown in Fig. 136), and in the mature placenta a complete endothelium-like lining is occasionally found in the sinus (Fig. 137). Nevertheless, this endothelium rests upon a necrotic substratum resembling an infarct and containing degenerating villi, and it is not impossible that the flat cells are derived from the epithelium of villi ; the question, however, needs further investigation.

The relations of the circulation in later stages are not essentially different from those that obtain in younger ova; in the mature expelled placenta also the intervillous space is, as a rule, but incompletely filled (Fig. 122) or almost empty (Fig. 129). Placentae fixed in situ are usually gorged with blood (Bloch, 1889). The circulation is determined, on the one hand, by the arrangement of the uteroplacental vessels, already described, and on the other, by the pregnancy pains already referred to (p. 136). The poverty in blood of the expelled placenta is further evidence of a comparatively well-determined circulation. In considering the growth of the placenta a distinction must be made between growth in thickness and growth in area. The growth in thickness is chiefly due to an elongation of the villi and the associated separation of the chorion plate from the basal plate.

Somewhat different from this is the view of Pfannenstiel (1903). As has already been pointed out, this author derives the syncytium from the endothelium of the maternal blood-vessels and regards the first-formed blood lacunfle as greatly enlarged capillaries; he terms them the primary intervillous space. This space then enlarges by the veins which open on its floor and into which bunches of villi project, enlarging as the result of a degeneration of their walls, this degeneration extending as far as the arteries which open between the veins; the tissue surrounding the arteries, however, persists to form the decidual pillars, that is to say, the septa placent«8. The new space so formed is termed the secondary intervillous space. The projection of villi into the veins is incontestable (see p. 164) ; the process assumed to occur by Pfannenstiel cannot, however, have any important significance, since, firstly, anchoring villi are at that time attached to the basal plate in the neighborhood of the openings of the veins and their attachment would be broken by such a degeneration, without the possibility of forming a new attachment after the destruction of the cell columns. Secondly, the basal plate is not thicker in the early stages of development than it is later, and such a melting away of the portion of it that is in relation to the intervillous space would require a very intensive proliferation of the decidua basalis for the replacement of the lost layers. But there is no histological evidence of the occurrence of such a proliferation.

The question of the growth in area of the placenta presents great difficulties, apart from that which occurs during the embryotrophic stage of placentation. The most important factor in this latter growth is the splitting of the marginal decidua, and the occurrence of this process makes it intelligible how the ovum, at first a mere dot but later increasing enormously in size, forms for itself a capsule, which projects beyond the level of the mucous membrane as far as the equator of the ovum or even beyond it and fills a considerable portion of the uterus. But the growth in area of the placenta is not confined to the embryotrophic period; the placenta reaches its greatest relative extent at about the fourth month (Von Herff), at which time it oCoupies almost the half of the inner surface of the uterus. At this time it is depressed in a cup-like manner, at the centre, in correspondence with the almost even curvature of the uterus. Later its growth is relatively less rapid than that of the uterus and it becomes flatter in correspondence with the stretching of the pregnant uterus and the slight flattening of its anterior and posterior walls. This, at first, rapid enlargement of the placenta has been regarded by Hitschmann and Lindenthal as the result of a gradual inclusion in the placenta of the decidua capsularis and the portions of the chorion frondosum opposite to it, there being at the same time a stretching of the summit of the capsularis and of the chorion loBve — in other words, it is due to a kind of unrolling and stretching of the chorion frondosum; but no evidence tliat such a process occurs is forthcoming. The possibility of a shifting of the margin of the placenta, as a result of unequal growth, is also worthy of consideration. Similarly, the later relative diminution of the placenta may be due to two different causes; either there is a degeneration of its marginal portions or there is again a shifting of the margin as the result of unequal growth.

Pfannenstiel chiefly inclines toward a shifting of the margin, which has, indeed, the greater probability ; yet the process cannot be a simple one on account of the manifold connections between the placenta and the subjacent tissues by means of the blood-vessels. The decidua basalis spongiosa with its large gland cavities forms, it is true, a very adaptable substratum. But an obliteration of the marginal portions in later stages is also very probable, since younger placentae (Fig. 130) show a relatively gradual transition into the chorion laeve and only later does a distinct placental margin appear. A solution of the problem may perhaps be obtained in the following manner: Villi are probably formed only in early stages by the ingrowth of mesoderm into the trophoblast shell (Hitschmann and Lindenthal) ; after the formation of the chorion plate and its two-layered epithelium the new-formation of villi must cease. The destruction of smaller villi in the subchorial fibrin stria is probable, but the larger ones must persist until the mature placenta, in which, as a rule, a villus corresponds to each cotyledon. An enumeration of the basally directed villi at different stages would show whether the placenta was enlarged by taking into its territory new portions of the chorion and later diminished by excluding them again, or whether a certain constancy in the numbers occurred. Such enumerations have not, however, as yet been attempted.

The situation of the placenta, which is determined at implantation, is just as frequently upon the anterior as upon posterior wall of the uterus ; more rarely it is lateral, in which case it may cover the opening of a tube.^^ according to Holzapfel (1898), in 107 cases the placenta was situated on the anterior wall in forty-two, on the posterior wall in forty-five ( both inclusive of cases of extramedian positions and extension upon the fundus), in a tubal angle in fourteen, laterally below the opening of a tube in five. One case was a placenta praevia (covering the os internum uteri), but this condition is of rare occurrence, since according to Schauta but one case occurs in 1500-1600 pregnancies. It may result from a persistence of a portion of the capsularis with its intervillous space and supply of villi (placenta reflexa), or from an abnormally low implantation of the ovum, near the ostium internum, or perhaps from a double implantation on both walls of the uterus at the same time, as has occasionally been observed (Graf Spee) in guinea-pigs (Hitschmann and Lindenthal).

V. The Mature Afterbirth - the Amnion, Allantois and Yolk Sack up to Maturity

The immediate causes of birth are still unknown, yet it may be said that in general the placenta is so altered at the close of pregnancy by the continued modifications of the epithelium of the villi, the disappearance of the Langhans layer and syncytium, the formation of fibrinoid and infarcts, that it can no longer perform its function of affording nourishment to the child, or can do so at best only insufficiently. The trophoblast and sjTicytium have a limited span of life and its close is reached with the close of pregnancy. The plane of separation of the afterbirth lies in the region of the decidua spongiosa, in which preparations for it have been made by anatomical conditions (the thin gland partitions) (Langhans) ; nevertheless, local separations occur also in the compacta, and, indeed, are regarded as the rule by Webster. The placenta, chorion laeve, and decidua compacta possess a certain amount of firmness and are actually separated from the spongiosa by any diminution of the inner surface of the uterus ; the result of this is the formation of a retroplacental hcematoma, which begins to be formed at the first rupture of the vessels.

The expelled placenta is, as a rule, disk-shaped and has a diameter of 16-20 cm., a thickness of 2i^^/^-3 cm., and an average weight of something over 500 Gm. Variations are not rare in all dimensions and do not stand in any aCourate relation to the development of the child. The maternal or outer surface (Fig. 135) after the removal of the adhering blood-clots appears dark reddish gray, frequently with small, somewhat pale spots; is divided by furrows into 15-20 irregular lobes (cotyledons) ; and is, in general, rather smooth, except for oCoasional adhering shreds of tissue (portions of the spongiosa). The paler spots correspond to anchoring villi and the bunches of villi which surround them, and the darker areas between them are caused by the blood of the intervillous space; yet these differences of color are evident only when the basal plate is relatively thin and the maternal blood has been retained in considerable quantity. Furthermore, small white scales (calcareous deposits), very variable in number, are usually to be seen; they usually occur in fibrin nodes (Figs. 127 and 129) and are usually near the basal plate. Larger white or yellowish masses projecting above the general surface are caused by the white infarcts. The uteroplacental vessels traverse the basal plate usually as greatly contorted canals (Bumm, Klein) ; the veins have a greater calibre and more delicate walls than the arteries. In each cotyledon there are about two or three veins situated centrally and from three to five peripheral arteries (see also p. 162). (Concerning the visibility of the choriodecidual vessels see p. 160.) The cotyledons are incompletely separated by the septa placentae, which extend from the furrows of the outer surface and by manipulation of the placenta, or even by birth-trauma, may be readily separated into two layers, so that the furrows appear markedly deepened.

" The covering of an opening of a tube is evidence in favor of the splitting of the decidua marginalis during the growth of the ovum.

The fetal inner surface is whitish, and at first is covered by the amnion; after this is removed it is rather smooth, with the fetal vessels projecting from the surface. A marking of the surface, usually visible, consisting of paler spots on a darker background, is due to the same causes as the corresponding marking of the outer surface, but is dependent, as regards its visibility, on the thickness of the subchorial layer of fibrin. From the surface project occasionally the placental cysts (p. 155) filled with a clear fluid. On section the fresh placenta is dark red and shows a spongy structure ; the septa as well as the basal plate are more grayish-red. The arrangement and size of the cotyledons are determined chiefly by the chorionic villi. In general, each cotyledon corresponds to a villus, which, with its branches, fills the cavity of the cotyledon and is attached by numerous anchoring villi to the basal plate and the septa. Close to the origin of the villus from the chorion plate branches are ^iven ofiF, which divide immediately beneath the plate and are frequently included in the Langhans stria and the canalized fibrin. Small or rudimentarv villi occur on the chorion plate only in the region of the placental margin.

The chorion (chorion Iseve) forms with the placenta a sack, which is opened in the afterbirth by a sht, often irregular or triradiate, and corresponding to the lower pole of the ovum. It is a grayishor yellowish-red, easily torn membrane, whose outer surface is rough and has attached to it shreds of decidua and blood-clots. Its microscopic structure, and also that of the placenta at birth, has been described in Section IV. Hyrtl describes in the chorion la-ve, close to the margin of the placenta, occasionally occurring arteriovenous anastomoses between fetal placental vessels of the size of a needle or more. The vessels which occurred in the chorion Ifeve when it still possessed villi have complete!;' disappeared at birth, so that the membrane is non-vascular; yet occasionally some weak stems occur in the marginal parts of the mature membrane.

The amnion is fused with the placenta and chorion, but may be separated from these as an independent, transparent, glistening membrane. After its separation its outer surface, and also the inner surface of the chorion, has a fibrillar appearance, as delicate connective-tissue strands which connect the two membranes have been torn by the separation. The amnion consists of a connectivetissue stroma and a cubical or cylindrical epithelium, in which Lonnberg finds fat granules of fre<|uent occurrence. Rarely (and principally in the placental region) the epithelium presents irregular whitish growths, the amniotic inlli (Fig. 138) (Ahlfeld), structures which are of normal occurrence in ungulates. The epithelium over them is many-layered and the cells undergo comification and desquamation. Blood-vessels are wanting in the amnion.

The fusion of the amnion and chorion is secondarily produced by the disappearance of the extra-embryonic coelom towards the end of the second month (Strahl), as the result of the rapid growth of the amniotic sack. The amniotic epithelium is at first quite low and endothelium-like, and becomes cubical only in the second half of pregnancy (Hondi). (Compare also Figs. 96, 114, and 117.) Granules appear in the cells after the third month and Bond! also describes granules in the mature amnion that staiu with neutral red. Stomata he could not find.

The liquor amnii, whose quantity amounts to about a litre at the end of pregnancy, is a secretion of the amniotic epithelium (Mandl, Bondi, Kreidl and Mandl). The evacuations of the fetal urinary bladder have no noteworthy significance in its production (compare also Wargaftig, 1907).

The umbilical cord (funiculus umbilicalis) is a cord which is usually twisted anti-clockwise (to the left) ; it is normally about the same length as the child, but may be reduced almost to nothing or may reach three times the normal length. The twisting depends upon the unequal growth of the two umbilical arteries, and this again is associated with the slight difference which exists in the diameters of the two arteries from the beginning and with the difference of blood-pressure in the arteries as a result of the difference in frictional resistance (Neugebauer). The embryo, which floats freely in the amniotic fluid and is almost sustained by it, is passively rotated as the result of the gradual twisting of the cord, and local growths of the arteries produce the false nodes which occur in this. The angle at which tlie cord is inserted into the placenta varies between 0° and 90"" and is greatest in cases where the insertion is central ; when the attachment is at an acute angle there occurs between the cord and the placenta what is known as Schultze's amniotic fold, produced by the incomplete apposition of the amnion to the cord and placenta, owing to the persistence of the yolk sack and its vessels.

Microscopically there may be distinguished upon the surface of the cord the single-layered cubical or flattened amniotic epithelium, in which, according to Koster, stomata occur ; the connectivetissue layer of the amnion is not distinguishable as a separate sheet. The stroma of the cord consists of a gelatinous tissue, Wharton's jelly, which is characterized by possessing stellate cells, resembling embryonic cells, a scanty development of fibrillae, and wide intercellular spaces. At the periphery and in the neighborhood of the vessels the tissue is arranged in concentric layers (Fig. 139). The vessels, especially the arteries, show stout longitudinal muscle-bundles beneath the circular musculature, and these, when contracted, form strong projections which facilitate the complete closure of the vessels when the cord is severed (Henneberg, Bucura). Vasa vasorum can be distinctly injected in the veins, according to Conner, and while they cannot be injected in the arteries yet their origins can be distinguished when the arteries are laid open. Nerves can be followed from the abdominal cavity of the child only to the umbilicus or a short distance beyond it; they do not occur in the free portion of the cord (Bucura). Finally, remains of the allantoic duct occur in the mature cord.

The allantoic duct is, according to Lowy, still hollow throughout its entire length in embryos with a greatest length of 8 mm., but has a very variable diameter, and in embryos of 9 mm. its lumen is partly obliterated toward the peripheral end, while in those of 14 mm. it is open only in a small portion of its extent and that portion is irregularly expanded ; even in the fourth month remains of the duct are still to be fonnd in the neighborhood of the embryo with a lumen and cubical epithelium (Fig. 139) ; and in the mature cord there are to be found oCoasional epithelial pearls and occasionally coils and lateral outpouchings as remnants of the duct.

The yolk stalk becomes divided shortly after the closure of the umbilicus. In the umbilical cord remains of it may be found up to the third month, but at maturity these remnants have probably completely vanished. Portions of the omphalomesenteric vessels, occasionally filled with blood, are also to be found in the third month and, rarely, they persist until the close of pregnancy (Lonnberg).

Keibel Mall 139.jpg

Fig. 139. — Central portion of a Irsaivenie wction o[ sn umbiliesi cord ol »n embryo of the fourth moDth (vertex-bnecb leosth 13'-^ cm.). The WhartomBc jelly ia Bmniedin ooaoentrio layers. A. u,md K.u., umbilioJvMKis: .lUir. sllaDtoicduct. Tbe yolk aUlk liudiMpiWMnl. X 30.

The yolk sack {vesicula urabilicalis) is a normal constituent of the mature afterbirth (B. S. Sehultze), but on account of its minuteness and the irregularity of its situation it is readily overlooked. It occurs between the chorion and amnion, on the placenta or the chorion la-ve, or even at the opposite pole of the ovum ; very rarely it even appears to lie in the umbilical cord itself (Lonnberg). Its variability in position is due to the length of the yolk stalk and the width of the exoCoelom. The Schtdtze amniotic fold may serve as a guide to it, but between the direction of the fold and the connecting line between the sack and the umbilical cord there may be a divergence of even 90° (Lonnberg). Maeroscopically the mature yolk sack is usually a round or oval, flattened, white or yellow body with a diameter of 1-5 mm. ; microscopically it presents a mesodermal investment and its contents are flake-like and partly calcified, but no epitiielium can be detected.

At the commencement of its development tlie yolk sack shows a certain amount of differentiation. The blood and the vessels of the ovum first appear in its wall and, later, for a considerable time it is a region of blood formation and consequently richly vascular (Fig. 140). Its epithelium forms gland-like invaginations (Graf Spee) or intra-epitheliai cysts, produced by cell degeneration (Fig. 140). (Compare also Branca.) Graf Spee also describes the occurrence of giant cells in the epithelium of younger stages and regards them as associated with the blood formation. according to Meyer and Jordan there occur at the end of the first month epithelial buds, solid or hollow outgrowths, which project into the mesoderm, yet these structures are rather variable in their occurrence. Later the epithelium becomes flat and, finally, degenerates with the thickening up of the contents of the vesicle.

Fig. 140 Human embryo of s greatest lenith of 9 mm. Cy., inlra^pithdial d-veeeel; Spl.. nplaDcbnopleure. X 300.

VI. The Uterus Post Partum

Since the plane of separation of the afterbirth passes through the decidua spongiosa, the numerous flattened gland cavities of the latter are opened at birth. In the region of the placenta the spongiosa is somewhat thinner than elsewhere (see p. 159). Hemorrhage from the opened vessels is prevented by the compression of the vessels within the contracted muscularis and the compressed mucosa, but blood-serum exudes for a considerable time from the opened tissue spaces. The epithelium of the superficial gland cavities, which Langhans believes is responsible for the renewal of the superficial epithelium of the mucous membrane, has little significance in this respect,^^ having undergone extensive modifications during pregnancy (p. 140). The regeneration is rather from the deepest gland zone, the limiting layer of His ; but since this is exposed only in spots, the more superficial layers of the spongiosa and the persisting remains of the compacta must be destroyed by coagulation necrosis and be expelled. Previously to their expulsion they form a whitish-yellow layer resting upon the mucous membrane and have been usually regarded as necrosed compacta. The line of demarcation between the necrotic and persisting layers **is formed by the basal surfaces of all the gland cavities occurring in its neighborhood, which thus later become the surface" (of the mucosa) (Wormser). This line becomes distinct on the second day after birth ; the expulsion of necrotic tissue begins on the fifth day and is completed everywhere on the tenth to the twelfth day after birth. The gaps between the gland cavities are covered over after the expulsion *'by lateral shifting, flattening, and amitotic increase" of the epithelium; mitoses seem to be at first entirely wanting. As the epithelium grows out from the deeper portions of the glands many-layered zones of epithelium and multinuclear masses of protoplasm are formed, and, at the same time, degenerations occur everywhere in the epithelium; the formation of vacuoles, shrinkage of the nuclei, and degeneration of cells and nuclei are frequently to be found at the surface. Mitoses first appear about two weeks after delivery, and, finally, probably only those epithelial cells persist which have been newly formed by the mitotic process. Leucocytes wander in rather large numbers through the mucous membrane. The decidua cells degenerate in the vicinity of the line of demarcation, probably by a fatty degeneration; and the connective tissue scaffolding thus persists as an empty mesh-work. This process Wormser terms areolar degeneration, and he imagines the meshes to be eventually reoCoupied by inwandering connectivetissue cells; this idea, however, is rather improbable. The decidual modifications which have occurred in the deeper layers of the mucous membrane disappear, tiie syncytial giant cells degenerate and vanish, and in two or three weeks after birth the regeneration of the mucous membrane, aCoompanied by an increase in its thickness, is so far completed that stroma, tubular glands, and a surface epithelium are already present; nevertheless, the epithelium continues to show degenerations and regenerations for some time.

  • The account priven here is principally based on the observations of Wormser (1906).

The mucous membrane of the cervix uteri becomes looser during pregnancy and shows serous infiltration and an increase in the glands, while after birth it presents zones of traumatic hemorrhages, the epithelium, however, being retained. Leucocytes also wander out through this mucous membrane in considerable numbers.

The muscularis uteri increases during pregnancy to about twenty-four times its original size, partly by hypertrophy (the formation of new fibres by the division of those already present) and partly by hyperplasia of the individual fibres (Kolliker). The reduction is produced by a diminution of the size of the fibres and perhaps also by the complete degeneration of some of them (Von Ebner).

The peritoneal covering of the uterus and of the parts in its neighborhood shows here and there during pregnancy decidua-like growths (Schmorl), and similar growths occur in the tunica albuginea of the ovaries (Lindenthal). The tubes, with the exception of increased blood-supply and some serous infiltration, are but little altered.

  1. 0. Schultze: Grundriss der Entwicklungsjjeschichte, 1897; Strahl: Embryonalhlillen der Sau^r iind Placenta, in Hertwi^s Handbuch, 1902; Bonnet: Lehrbuch der Entwickliingfs^schicbte, 1907, and, most recently, 0. Grosser: Vergleichende Anatomie und Entwicklungsgreschicbte der Eihaute und der Placenta, Lehrbucb fiir Studierende und Aerzte, Wien, 1909. From this last work the majority of the illustrations of this chapter have been taken. A very complete list of the literature on human placentation is to be found in the work of F. Keibel and C. Elze: Normentafel des Menschen, Jena, 1908.
  2. In some mammals also from the yolk sack. according to the view of Hubrecht (see especially Resink, Tijdschrif t Ned. Dierk. Vereen, 1903, 1905 : Hubrecht, Quart. Joum. Micr. Sc, 1909), however, the chorion possesses from the beginning a vasifactive mesoderm. Compare Grosser's Lehrbuch.
  3. As a rule, however, the term decidua is not only applied to the superficial layer which is expelled, but also includes the entire thickness of the mucous membrane. This is the case with its application to the human placenta.
  4. In Hertwig's Handbuch, 1902, and recently in a fuller somewhat modified statement in Der Uterus puerpuralis von Erinaceus europcetts, Verhandl. K. Ak. Wetensch., Amst., 1907.
  5. Verh, morph. Gesellsch., Wien, 1908; Zentralblatt fiir Physiologie, 1908; and Lefirbuch.
  6. A modification of this statement is necessary in connection with the maternal blood. See below.
  7. Holsti (1908) lays special weight upon fatty degeneration of the decidua, upon fat formation in the glands, and npon the transportation of fat from other orerans by leucocytes; this fat is directly absorbed by the chorionic epithelium up to the close of pregnancy.
  8. Hubrecht, however, in his earlier works (Plaeentation of the Hedgehog, 1890) employed the expression to denote only the proliferating chorionic ectoderm. Compare Hubrecht, Science, 1904, and foot-note 2.
  9. These authors cite the literature of the question.
  10. Disse, who has subsequently studied the specimen, regards the entire trophoblast of the ovum as maternal tissue and also transfers this same interpretation to the Peters ovum.


Ahlfeld, F. : Ueber die Zotten des Amnion, Archiv f. Gynak., vol. vi, 1874. Zur Genese der Amnionzotten, ibid., vol. vii, 1875.

Bab, H. : Konzeption, Menstruation u. Schwangerschaf t, Deutsche med. Woch., 1908.

Beneke: Ein sehr junges menschliches Ei. Deutsche med. Wochenschr., Jahrg. 30, 1904; also Monatsschr. f. Geb. und Gyn., vol. xix, 1904.

Bloch: Ueber den Bau der menschlichen Placenta, Beitr. z. path. Anat., vol. iv, 1889.

BoNDi, J.: Zur Histogenese des Amnionepithels, Zentralbl. f. Gynak., Jahrg. 29, 1905.

Bonnet, R. : Ueber Syncytien, Plasmodien und Symplasma in der Placenta der Saugetiere und des Menschen, Monatsschr. f . Geb. und Gyn., vol. xviii, 1903. Lehrbueh der Entwicklungsgeschichte, Berlin, 1907.

Branca, A. : Sur Tendoderme ombilical de Fembryon humain, Bibl. Anat. Supplement, 1908 (C. R. Ass. Anat.).

Bryce, T. H., and Teacher, J. H. : An Early Ovum Imbedded in the Decidua; also conjointly with J. M. Munro Kerr, An Early Ovarian Pregnancy, under the title: Contributions to the Study of the Early Development and Imbedding of the Human Ovum, Glasgow, 1908.

BucuRA, C. : Ueber den physiologischen Verschluss der Nabelarterien und iiber das Vorkommen von Langsmuskulatur in den Arterien des weiblichen Genitales, Zentralbl. f. Gynak., Jahrg. 27, 1903. Ueber Nerven in der Nabelschnur und in der Placenta, Zeitschr. f . Heilkunde, vol. xxviii, 1907. (See also Zentralbl. f. G3mak., vol. xxxii, 1908.)

BuMM, E. : Ueber Uteroplacentargefasse, Archiv f. Gynak., vol. xxxv, 1889. Ueber die Entwicklung des miitterlichen Blutkreislaufes in der menschlichen Placenta, Archiv f. Gynak., vol. xliii, 1893.

Busalla : Beschreibung und histologisches Untersuchungsergebnis eines neuen Falles von Eierstocksschwangerschaft, Archiv f. Gynak., vol. Ixxxiii, 1907.

CovA, E. : Ueber ein menschliches Ei der zweiten Woche, Archiv f. Gynak., vol. Ix2udii, 1907.

Dissey J.: Die Eikammer bei Nagem, Insektivoren und Primaten, Ergebnisse d. Anat. und Entw., vol. xv for 1905, Wiesbaden, 1906.

Fossati, G.: Ueber Nerven in der Nabelschnur und in der Placenta, Zentralbl. f. Gynak., vol. xxxi, 1907.

FBANQui, 0. v.: Die Entstehung der velamentosen Insertion der Nabelschnur, Zentralbl. f. Gynak., 1901.

Frassi, L. : Ueber ein junges menschliches Ei in situ, Archiv f . mikrosk. Anatomie, vol. Ixx, 1907. Weitere Ergebnisse des Studiums eines jungen menschlichen Eies in situ, ibid., vol. Ixxi, 1908.

Friolet, H. : Beitrag zum Studium der menschlichen Placentation, Beitrage z. Geburtsh. u. Gynak., vol. ix, 1904; also Dissert., Basel.

Fuss, S.: Die Bildung der elatischen Faser, Arch. f. pathol. Anat, vol. clxxxv, 1906.

Giese, H. : Histologische Untersuchungen iiber den weissen Infarkt der Placenta, Dissert., Halle, 1905.

Goenner, A. : Ueber Nerven und emahrende Gefasse im Nabelstrang, Monatsschr. f. Geburtsh. u. Gynak., vol. xxiv, 1906.

Grosser, O.: Vergleichende Anatomie und Entwicklungsgeschichte der Eihaute und der Placenta mit besonderer Beriicksichtigung des Menschen, Lehrbuch f iir Studierende und Aerzte, Wien, 1909.

Happe, H. : Beobachtungen an Eihauten junger menschlicher Eier, Anat. Hefte, vol. xxxii, 1906.

Henneberg, B. : Beitrage zur feineren Struktur, Entwicklungsgeschichte und Physiologic der Umbilicalgefasse des Menschen, Anat. Hefte, vol. xix, 1902.

Herfp, 0. v.: Beitrage zur Lehre von der Placenta und von den miitterlichen Eihiillen, Zeitschr. f. Geb. u. Gyn., vol. xxxv, 1896, and vol. xxxvi, 1897.

Hitschmann, F. : Die Deportation der Zotten und ihre Bedeutung, Zeitschr. f. Geb. u. Gyn., vol. liii, 1904.

Hitschmann, F., and Lindenthal, 0.: Ueber das Wachstum der Placenta, Zentralbl. f. Gynak., 1902.

Ueber die Haftung des Eies an atypischem Orte, ibid,, 1903.
Der weisse Infarkt der Placenta, Archiv f. Gynak., vol. Ixix, 1903.

Hofbauer, T. : Grundziige einer Biologic der menschlichen Placenta mit besonderer Beriicksichtigung der Fragen der fetalen Emahrung, Wien u. Leipzig, 1905 (literature). Die menschliche Placenta als Assimilationsorgan, 1907.

Hopmeier, M. : Die menschliche Placenta, Wiesbaden, 1890.

HoLL, M. : Ueber die Blutgefasse der menschlichen Nachgeburt, Sitz-Ber. k. Akad. Wiss., Wien, vol. Ixxxiii, 1881.

HoLSTi, O. N. : Weitere Beitrage zur Kenntnis der Embryotrophe, II. Ueber die Fettzufuhr zum menschlichen Ei, Anat. Hefte, vol. xxxiii, 1908.

HoLZAPFEL, K. : Ueber den Placentarsitz, Beitrage z. Geburtsh. u. Gynak., vol. i, 1898. Zur Pathologic der Eihaute, Beitr. zur Geburtsh. und Gynak., vol. viii, 1903. (The author regards the amniotic villi as transplanted embryonic epidermis.)

Hyrtl, J. : Die Blutgefasse der menschlichen Nachgeburt in normalen und abnormen Verbal tnissen, Wien, 1870. IwASE, Y. : Ueber die zyklische Umwandlung der Uterusschleimhaut, Zeitschr. f. Geburtsh. und Gynak., vol. Ixiii, 1908.

Jordan, H. E. : The Histology of the Yolk-sac of a 92-mm. Human Embryo, Anat. Anzeiger, vol. xxxi, 1907. Jung, Ph.: Beitrage zur fruhesten Ei-Einbettung beim menschlichen Weibe, Berlin, 1908. Vol. I.— 12

BIastschenko, N.: Das menschliche Chorionepithel und dessen Rolle bei der Histogenese der Placenta, Archiv f. Anat. u. Phys., Anat. Abt., 1885.

Kehrer, E. : Der placentare Stoffaustausch in seiner pbysiologischen und pathologischen Bedeutung, Wiirzburger AbhandL, vol. vii, parts 2 and 3, 1907 (literature).

Klein, G. : Mikroskopisches Verhalten der Uteroplacentargefasse, in Hofmeier: Die menschlicbe Placenta, Wiesbaden, 1890. Zur Entstehung der Placenta marginata und suCoenturiata, ibid.

Kollmann, J.: Kreislauf der Placenta, Chorionzotten und Telegonie, Zeitschr. f. Biologie, vol. xlii, 1902.

Langhans, Th. : Zur Kenntnis der menschlichen Placenta, Archiv f. Gynak., vol. i, 1870. Untersuchungen iiber die menschlicbe Placenta, Archiv f. Anat. u. Phys., Anat. Abt., 1877. Ueber die Zellschicht des menschlichen Chorion, Festschr. f . Henle, Beitrage z. Anat. u. Embryol., Bonn, 1882. Syncytium und Zellschicht, Beitrage z. Geburtsh. u. Gynak., vol. v, 1901.

Leopold, G. : Uterus und Kind, mit Atlas, Leipzig, 1897. Ueber ein sehr junges menschliches Ei in situ, Leipzig, 1906.

Leopold and Ravano : Neuer Beitrag zur Lehre von der Menstruation und Ovulation, Archiv f. Gynak., vol. Ixxxiii, 1907.

LoNNBBRO, J. : Studien iiber das Nabelblaschen an der Nachgeburt des ausgetragenen Kindes, Stockholm, 1901 (literature).

Mandl, L. : Histologische Untersuchungen iiber die sekretorische Tatigkeit des Amnionepithels, Zeitschr. f. Greb. u. Gyn., vol. liv, 1905. Weitere Beitrage zur Kenntnis der sekretorischen Tatigkeit des Amnionepithels, ihid., vol. Iviii, 1906.

Marchand, F. : Beobachtungen an jungen menschlichen Eiem, Anat. Hefte, vol. xxi, 1903. Beitrag zur Kenntnis der normalen und pathologischen Histologic der Decidua, Archiv f. Gynak., vol. Ixxii, 1904.

Mebttens, J.: Beitrage zur normalen and pathologischen Anatomie der menschlichen Placenta, Zeitschr. f. Geb. u. Gyn., vol. xxx, 1894, and vol. xxxi, 1895.

Meyer AW. On the structure of the human umbilical vesicle. (1904) J. Anat. 3(2):155-166.

Minot CS. Uterus And Embryo - I. Rabbit II. Man. (1889) J Morphol. 2:

Minot CS. Implantation of the human ovum in the uterus. (1904) Trans. Am. Gynec. Soc., Philadelphia, 29: 395-402.

Neugebauer, L. a. : Morphologic der menschlichen Nabelschnur, Breslau, 1858.

Nitabuch, R. : Beitrage zur Kenntnis der menschlichen Placenta, Dissert., Bern, 1887.

Peters, H. : Ueber die Einbettung des menschlichen Eies und das f riiheste bisher bekannte menschliche Placentationsstadium, Leipzig and Wien, 1899 (literature).

Zum Kapitel: LanghansVhe Zellschicht, Zentralbl. f. Gyniik., 1900. Beitrag zur Kasuistik der Vasa praevia und Gedanken zur Theorie der Insertio velamentosa, Monatsschr. f. Geb. u. Gyniik., vol. xiii, 1901.

Pfannenstiel, J.: Die ersten Veranderungen der Gebarmutter infolge der Schwangerschaft, — Die Einbettung des Eies, — Die Bildung der Placenta, der Eihiiute und der Nabelschnur, — Die weiteren Veranderungen der genannten Gebilde wahrend der Schwangerschaft, in Winckel: Handbuch der Geburtshilfe, vol. i, Wiesbaden, 1903 (literature).

Reinstein-Mogilowa, a.: Ueber die Beteiligung der Zellschicht des Chorions an der Bildung der Serotina und Refiexa, VirchoVs Archiv, vol. cxxiv, 1891.

ROHBy K. : Die Beziehungen der miitterlichen Gefasse zu den intervillosen Raumen der reifen Placenta, speziell zur Thrombose derselben (weisser Infarkt), Virchow's Archiv, vol. cxv, 1889.

Rossi-DORIA, J.: Ueber die Einbettung des menschlichen Eies, studiert an einem kleinen Ei der zweiten Woche, Archiv f , Gynak., voL Ixxvi, 1905.

RuGE, C. : Die Eihiillen des in der Geburt befindlichen Uterus, Bemerkungen iiber den Ort und die Art der Emahrung des Kindes in demselben, in :

Schroeder, K. : Der schwangere und kreissende Uterus, Beitrage zur Anatomic und Physiologic der GJeburtskunde, mit Atlas, Bonn, 1886.

ScHiCKELE, G. : Die Chorionektodermwucherungen der menschlichen Placenta, ihre Beziehungen zur Entstehung der Cysten und Fibrinknoten der Placenta, Beitr. z. Geb. u. Gyn., vol. x, 1905.

Sellheim, H. : Physiologic der weiblichen Geschlechtsorgane, in Nagel, Handbucb der Physiologie, vol. ii, 1907.

Siegenbeek van Heukelom: Ueber die menschliche Placentation, Arch. f. Anat. u. Phys., Anat. Abt., 1898.

Spee, F., Graf: Ueber die menschliche Eikammer und Decidua reflexa, Anat. Anzeiger, vol. xiv, Suppl., 1898. Neue Beobachtungen iiber sehr friihe Entwicklungsstufen des menschlichen Eies, Arch, f . Anat. u. Phys., Anat. Abt., 1896. Epidiaskopische Demonstration eines jungen Stadiums der menschlichen Eieinbettung, Verhandl. Deutsch. Gea f. Gynak., xi Meeting in Kiel, 1905, Leipzig, 1906.

Steffeck, p.: Der weisse Infarkt der Placenta, in Hofmeier: Die menschliche Placenta, Wiesbaden, 1890.

Stolper, L.: Zur Physiologie und Pathologie der Placentation, Monatsschr. f. Qeh, u. Gyn., vol. xxiv, 1906.

Strahl, H. : Die menschliche Placenta, Ergebnisse d. Anat. u. Entwickl., vol. ii, 1893 (literature). Neues iiber den Bau der Placenta, ibid,, vol. vi, 1897 (literature). Placentaranatomie, ibid., vol. viii, 1899 (literature). Die Embryonalhiillen der Sauger und die Placenta, Hertwig's Handbuch der vergl. u. experiment. Entwicklungslehre, vol. i, part ii, Jena, 1906 (published 1902) (literature). Der Uterus post partum, Ergebnisse d. Anat. u. Entw., vol. xv, 1906 (literature). Van Cauwenberghe, Recherches sur le role du syncytium dans la nutrition embryonnaire de la femme. Archives de Biol., vol. xxiii, 1907 (literature).

VoiGT, J. : Ueber das Verhalten von miitterlichen und kindlichen Elementen an der Einnistungsstelle j lingerer menschlicher Eier, Zeitschr. f. Geburtsh. u. Gynak., vol. liv, 1905.

Waldeyer, W. : Ueber den Plaeentarkreislauf des Mensehen, Sitz.-Ber. k. preuss. Akad. Wiss., 1887. Bemerkungen iiber den Bau der Mensehenund Affenplacenta, Archiv f. mikr. Anat., vol. xxxv, 1890 (literature).

Wargaftig, Gr. : Der augenblickliche Stand der Lehre von der Herkunft, der Physiologie und Pathologie des Fniehtwassers, Diss., Freiburg, i. Br., 1907.

Webster, J. C. : Human Placentation, Chicago, 1901. Die Placentation beim Mensehen, Transl. by Koliseher, Berlin, 1906.

Wederhake, J.: Ueber Plasmaund Deciduazellen, Monatsschr. f. Geburtsh. u. Gynak., vol. xxiv, 1906.

Wolska, W.: Ueber die von Ruge beschriebene fetale Vaskularisation der Serotina, Dissert., Bern, 1888.

Wormser, E. : Die Regeneration der Utenisschleimhaut nach der Geburt, Archiv f. Gynak., vol. Ixix, 1903 (literature).

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