The fundus is now lower than it was in the preceding month, being about half way between the scrobiculus cordis and umbilicus; the abdomen has, as it is called, _fallen_; and from the diaphragm being now able to resume its functions the breathing becomes more easy, and the female feels more comfortable and capable of moving about. On examination per v.a.g.i.n.am the anterior portion of the inferior segment of the uterus will be felt still deeper in the pelvis: if the head presents it distends this part of the uterus, so that, in many cases, we have to pa.s.s the finger round it before we can reach the os uteri, which is now in the upper part of the hollow of the sacrum. All traces of the cervix have now disappeared, it having been required to complete the full development of the uterus; the situation of the os uteri itself is marked merely by a small depression or dimple; there is no longer any distinction between the os uteri internum and externum; the edges of the opening are so thin as to be nearly membranous, but remain closed in primiparae until the commencement of labour.[16]

In women who have had several children, a considerable difference is observed as regards the state of the cervix and os uteri: the cervix does not undergo that shortening during the latter half of pregnancy, which is the case in a primipara, a portion of it at least remaining up to the full term of utero-gestation: in many cases, especially where the female has had a large family, it is nearly an inch long at this period; nor is the lower portion of the uterus so spherical as in the primipara; to this circ.u.mstance may probably be attributed the fact of the head not descending so deep into the pelvis just before labour. In multiparae the os uteri is also very different: instead of being perfectly round with its edges smooth, it is irregular and uneven, and seldom loses altogether the lip-like shape of the unimpregnated state in consequence of the greater thickness and elongation of its lips from former labours; its edges here and there is uneven and knotty, from little callous cicatrices, where it has been torn; moreover it does not remain closed till the commencement of labour, but the os uteri externum (commonly called os tincae,) and sometimes even the os uteri internum will be more or less open during the last three or four weeks of pregnancy. These peculiarities are of great importance in coming to a conclusion as to whether a patient be in her first pregnancy or not: although not invariable in the utmost sense of the word, still their occurrence, even after a single labour, is sufficiently frequent to make them worthy of careful observation. Indeed, on more than one occasion, we have known them occur even after a miscarriage, a circ.u.mstance on the strength of which the patient had ventured to deny that she was pregnant. On the other hand, we sometimes meet with the os uteri in a second pregnancy so little altered by the effects of the previous labour, that it would be extremely difficult to come to a decision.

When labour is over, the uterus contracts very considerably, and, in a few days after, its parietes will be found at least an inch in thickness. It now gradually diminishes in size, and continues to do so for some weeks; the blood-vessels contract, and losing the peculiarly loose spongy structure of pregnancy it becomes harder, firmer, and more compact. It nevertheless remains softer and larger than in the virgin state, and does not attain its original size and hardness until an advanced period of life.

The os uteri, which in the latter months of pregnancy had formed a circular opening, resumes its former shape, except that its lips, especially the posterior one, which are more or less irregular and uneven, are thicker and longer than in the virgin state. For the first weeks after labour, the os uteri is high in the pelvis, soft, and easily admits the tip of the finger; at the end of the second week it is much lower in the pelvis, and no longer permits the finger to pa.s.s. Immediately after labour, the contracted uterus forms a hard solid ball, the size of a new-born child's head; this state of contraction is not, however, of long continuance: in the course of half an hour, or even less, it begins to increase in size, becoming softer and larger, and continuing to increase slowly for some hours, when it again gradually diminishes, until, as before observed, it approaches its original size in the unimpregnated state. The state of powerful contraction in which the uterus is felt immediately after labour, after a time gradually relaxes; its spongy texture, from which the blood had been forcibly expelled by the violent action of its fibres, becomes again filled with blood; the organ swells and becomes softer and more bulky, and the orifices of the vessels which open into the cavity of the uterus are again partly pervious, and emit a sanious fluid called the _lochia_. This state lasts for two or more days after delivery, when the vessels begin to recover their former caliber, and lose that degree of dilatation peculiar to the gravid state. The lochia become less and less coloured, and now, and not before the uterus undergoes that gradual diminution of size and bulk which we have just alluded to.

The copulative or external organs of generation are the _v.a.g.i.n.a_, _hymen_, _c.l.i.toris_, _nymphae_, and _l.a.b.i.a_, the three last being known by the term _v.u.l.v.a_.

_v.a.g.i.n.a._ The v.a.g.i.n.a is a ca.n.a.l of about four inches in length and one in breadth, broader above than below; its parietes are thin and are immediately connected with the uterus. It envelopes the portio v.a.g.i.n.alis of the uterus at its upper or blind extremity (fundus v.a.g.i.n.ae,) and is continuous with its substance; inferiorly, where it is narrowest, it pa.s.ses into the v.u.l.v.a. It is situated between the bladder and r.e.c.t.u.m, and attached to each by loose cellular tissue. Its direction differs from that of the uterus, for its axis corresponds very nearly with that of the pelvic outlet, running downwards and forwards. Posteriorly it is somewhat convex, anteriorly concave.

The v.a.g.i.n.a consists of two layers; the external, which is very thin, firm, of a reddish-white colour, and continuous with the fibrous tissue of the uterus; and a lining mucous membrane which is closely united to it. This latter is much corrugated, especially in the virgin state, the rugae running transversely in an oblique direction, and gathered together on its anterior and posterior surface, forming the _columna rugarum anterior and posterior_, which appear to be a continuation of the corrugations which form the arbor vitae of the cervix.

In the upper part of the v.a.g.i.n.a there are considerable mucous follicles, which moisten the ca.n.a.l with their secretion, and which during s.e.xual intercourse, and particularly during the first stage of labour, pour forth an abundant supply of colourless mucus for the purpose of lubricating the v.a.g.i.n.a, and rendering it more dilatable. Near its orifice, especially at the upper part, the veins of the v.a.g.i.n.a form the _plexus retiformis_, a congeries of vessels which has almost a cellular appearance, and from this reason has been called the _corpus cavernosum_ of the v.a.g.i.n.a; it appears to be capable of considerable swelling from distension with blood, like the corpus cavernosum p.e.n.i.s, and by this means serves to contract still farther the os externum during the presence of venereal excitement. A similar disposition to form plexuses of vessels is seen in the venous circulation of the nymphae, bladder, and r.e.c.t.u.m.

_Hymen._ The lining membrane of the v.a.g.i.n.a is of a reddish-gray colour, interspersed here and there, especially at its upper part, with livid spots like extravasation. At the os externum it forms a fold or duplicature called _hymen_, running across the sides of the posterior part of the opening, and usually of a crescentic figure, the cavity looking upwards. The duplicatures of membrane are united by cellular tissue. In some instances, the hymen arises from the whole circ.u.mference of the os externum, having a small orifice in the centre for the escape of the menses and v.a.g.i.n.al secretions: in some rare cases it is cribriform; and in others it completely closes the v.a.g.i.n.al entrance. When torn in the act of s.e.xual intercourse, it generally forms three or four little triangular appendages, called _carunculae myrtiformes_, arising from the posterior and lateral portions of the os externum.

From the ident.i.ty of its fibrous coat with that of the uterus, the v.a.g.i.n.a possesses considerable powers of contraction, when excited by the presence of any body which distends it; hence it is a valuable a.s.sistance to the uterus during labour: it also stands in the same relation to the abdominal muscles that the r.e.c.t.u.m does, so that as soon as it is distended by the head, &c. it calls them into the strong involuntary action, which characterizes the bearing down pains of the second stage of labour. The orifice of the v.a.g.i.n.a (os externum) is surrounded by a thin layer of muscular fibres, which arise from the anterior edge of the sphincter ani; they enclose the outer margin of the v.a.g.i.n.a, cover its corpus cavernosum, and are inserted into the crura c.l.i.toridis at their union. It has been called the sphincter or constrictor v.a.g.i.n.ae, and a.s.sists the corpus cavernosum still farther in contracting the os externum.

_c.l.i.toris._ The c.l.i.toris is an oblong cylindrical body, situated beneath the symphysis pubis, arising from the upper and inner surface of the ascending rami of the ischium, by means of two crura of about an inch long, and uniting with each other at an obtuse angle. It terminates anteriorly in a slight enlargement, called the _glans c.l.i.toridis_, which is covered with a thin membrane or a loose fold of skin, viz. the _preputium c.l.i.toridis_. It is a highly nervous and vascular organ, and like the p.e.n.i.s of the male, is composed of two crura and corpora cavernosa, which are capable of being distended with blood; they are contained in a ligamentous sheath, and have a septum between them. The c.l.i.toris is also provided with a suspensory ligament, by which it is connected to the ossa pubis. Like that of the p.e.n.i.s, the glans c.l.i.toridis is extremely sensible, but has no perforation. Upon minute examination, it will be found that the gland is not a continuation of the posterior portion of the c.l.i.toris, but merely connected with it by cellular tissue, vessels, and nerves; the posterior portion terminates on its anterior surface in a concavity which receives the glans. In the glans itself there is no trace of the septum, which separates the corpora cavernosa. On the dorsum of the c.l.i.toris several large vessels and nerves take their course, and are distributed upon the glans, and upon its prepuce are situated a number of mucus and sebaceous follicles.

The crura c.l.i.toridis at their lower portion are surrounded by two considerable muscles, called the erectores c.l.i.toridis, arising by short tendons close beneath them from the inner surface of the ascending ramus of the ischium, and extending nearly to their extremity.

_Nymphae._ The _nymphae_ or _l.a.b.i.a pudendi interna_, are two long corrugated folds, resembling somewhat the comb of a c.o.c.k, arising from the prepuce and glans c.l.i.toridis, and remaining obliquely downwards and outwards along the inner edge of the l.a.b.i.a, increasing in breadth, but suddenly diminishing in size. At their lower extremity they consist of a spongy tissue, which is more delicate than that of the c.l.i.toris, but resembles considerably that of the glans, of which it appears to be a direct continuation. It has been called the _corpus cavernosum nympharum_, and is capable of considerable increase in size when distended with blood. The two crura of the prepuce terminate in their upper and anterior extremities; they are of a florid colour, and in their natural state they are contiguous to, and cover the orifice of the urethra. The skin which covers them is very thin and delicate, bearing a considerable resemblance to mucous membrane, especially on their inner surface, where it is continuous with the v.a.g.i.n.a; externally it pa.s.ses into the l.a.b.i.a.

The s.p.a.ce between the nymphae and edge of the hymen is smooth, without corrugation, and is called _vestibulum_.

Close behind the c.l.i.toris, and a little below it, is the orifice of the urethra, lying between the two nymphae: it is surrounded by several lacunae or follicles of considerable depth, secreting a viscid mucus; its lower or posterior edge is, like the lower portion of the urethra, covered by a thick layer of cellular tissue, and a plexus of veins, which occasionally become dilated and produce much inconvenience; it is this which gives the urethra the feel of a soft cylindrical roll at the upper part of the v.a.g.i.n.a; and in employing the catheter, by tracing the finger along it, the orifice will be easily found.

_l.a.b.i.a._ The l.a.b.i.a extend from the p.u.b.es to within an inch of the a.n.u.s, the s.p.a.ce between the v.u.l.v.a and a.n.u.s receiving the name of _perineum_.

The opening between the l.a.b.i.a is called the _fossa magna_: it increases a little in size and depth, as it descends, forming a scaphoid or boat-like cavity, viz. the _fossa navicularis_.

The l.a.b.i.a are thicker above, becoming thinner below, and terminate in a transverse fold of skin, called the _fraenulum perinei_, or _fourchette_, the edge of which is almost always slightly lacerated in first labours.

They are composed of skin cushioned out by cellular and fatty substance, and lined by a very vascular membrane, which is thin, tender, and red, like the inside of the lips; they are also provided with numerous sebaceous follicles, by which the parts are kept smooth and moist.

CHAPTER III.

DEVELOPMENT OF THE OVUM.

_Membrana decidua.--Chorion.--Amnion.--Placenta.--Umbilical cord.--Embryo.--Foetal circulation._

_Membrana decidua._ The earliest trace of impregnation which is to be observed in the cavity of the uterus, and even before the ovum has reached it, is the presence of a soft humid paste-like secretion, with which the cavity of the uterus is covered, and which is furnished by the secreting vessels of its lining membrane. This is the _membrana decidua_ of Hunter: properly speaking, it should be called the _maternal membrane_, in contra-distinction to the chorion and amnion, which, as belonging peculiarly to the foetus, are called the _foetal_ membranes.[17]

Although at first in a semi-liquid state, it soon becomes firmer and more compact, a.s.suming the character of a membrane: it appears to be nothing else than an effusion of coagulable lymph on the internal surface of the uterus, having "scarcely a more firm consistence than curd of milk or coagulum of blood." (Hunter, _op. cit._ p. 54.) Hence, although much thicker than the other membranes, it is weaker; it is also much less transparent.

It is not of an equal thickness, being considerably thicker in the neighbourhood of the placenta than elsewhere; inferiorily, and especially near the os uteri, it becomes thinner: during the first weeks of pregnancy it is much thicker than afterwards, becoming gradually thinner as pregnancy advances, until it is not half a line in thickness. In the earlier months its external surface is rough and flocculent, but afterwards it becomes smoother as its inner surface was at an earlier period.

It is much more loosely connected with the uterus during the first months of pregnancy than afterwards, and this is one reason why premature expulsion of the ovum is more liable to take place at this period than during the middle and latter part of utero-gestation. It is more firmly attached to the uterus in the vicinity of the placenta than any where else, which is owing to the greater number of blood-vessels it receives from the uterus at this point; whereas commonly "it has no perceptible blood-vessels at that part which is situated near the cervix uteri,"

(_Ibid._,) this portion being much more loosely connected with the uterus.

The course which the decidual vessels take on coming from the inner surface of the uterus is admirably adapted to render the attachment of this membrane to it as firm as possible.

[Ill.u.s.tration: Vascularity of the decidua. _From Baer._]

Upon examining the lining membrane of the uterus at a very early period, when the decidua was still in a pulpy state, Professor v. Baer observed[18] that its villi, which in an unimpregnated state are very short, were remarkably elongated: between these villi, and pa.s.sing over them, was a substance, not organized but merely effused, and evidently the membrana decidua at an extremely early age. The uterine vessels were continued into this substance, and formed a number of little loops round the villi, thus anastomosing with each other. On account of this reticular distribution it was impossible to distinguish arteries from veins; there is evidently the same relation between the uterus and the decidua as between an inflamed surface and the coagulable lymph effused upon it.

[Ill.u.s.tration: Decidual cotyledons. _From Dr. Montgomery._]

Professor v. Baer considers that at a later period the connexion between the decidua and mucous membrane becomes so intimate, that it is impossible to separate the former without also separating the latter from the fibrous tissue of the uterus. This, we apprehend, is the stratum which, as Dr.

Hunter observes, "is always left upon the uterus after delivery, most of which dissolves and comes away with the lochia." He does not appear to have been fully aware of the close connexion between the decidua and lining membrane of the uterus, although he evidently observed the fact from the following sentence: "in separating the membranes from the uterus we observe that the adhesion of the decidua to the chorion, and likewise its adhesion to the _muscular fibres of the uterus_, is rather stronger than the adhesion between its external and internal stratum, which, we may presume, is the reason that in labour it so commonly leaves a stratum upon the inside of the uterus." According to the observations of Dr.

Montgomery, a great number of small cup-like elevations may be seen upon the external surface of the decidua vera, "having the appearance of little bags, the bottoms of which are attached to, or embedded in, its substance; they then expand or belly out a little, and again grow smaller towards their outer or uterine end, which, in by far the greater number of them, is an open mouth when separated from the uterus: how it may be while they are adherent, I cannot at present say. Some of them which I have found more deeply embedded in the decidua were completely closed sacs. They are best seen about the second or third month, and are not to be found at the advanced periods of gestation."[19]

[Ill.u.s.tration: _a_ Uterus. _d_ Decidua reflexa. _b_ Fallopian tube. _e_ Ovum. _c_ Decidua.]

The membrana decidua does not envelope the ovum with a single covering, but forms a double membrane upon it, somewhat like a serous membrane; in fact, the descent of the ovum through the Fallopian tube is very similar to that of the t.e.s.t.i.c.l.e through the inguinal ca.n.a.l into the s.c.r.o.t.u.m. The ovum pushes before it that portion of the decidua which covers the uterine extremity of the Fallopian tube, and enters the cavity of the uterus, which is already lined with decidua, covered by the protruded portion which forms the _decidua reflexa_. It must not be supposed that this reflexion of the decidua is completed as soon as the ovum enters the uterine cavity; the ovum usually remains at the mouth of the Fallopian tube, from which it has emerged, covered by the plastic ma.s.s of soft decidua, and the reflexion of this membrane will take place in proportion as the ovum gradually increases in size. The external layer of decidua is called _decidua vera_; the internal or reflected portion is called the _decidua reflexa_, having received this appellation from its discoverer, Dr. Hunter. These membranes would, as Dr. Baillie has correctly observed, be more correctly named the _decidua uteri_ and _decidua chorii_: the decidua chorii or reflexa is reflected inwardly from above downwards; it is connected on its inner surface with the chorion: externally it is unattached, whereas, the decidua uteri or vera is unconnected on its inner surface, but attached to the uterus externally.

The membrana decidua differs in its arrangement from that of a serous membrane, inasmuch, as it is not only reflected so as to cover the chorion, but at the point of reflexion it is continued over the chorion externally, where it forms the placenta, so that the chorion is enclosed in all directions by the decidua: this latter portion, however, is not formed till about the middle of pregnancy. The decidua uteri or vera does not extend farther than the os uteri internum, which is filled up by the plug of tough gelatinous substance above described; the decidua chorii or reflexa, from its forming the outer covering of the chorion, of course pa.s.ses over the os uteri.

[Ill.u.s.tration: _Membrana decidua._

The lower orifice corresponds to the os uteri, the two upper ones to the Fallopian tubes. _From Dr. Hunter._]

According to Mr. John Hunter, the decidua vera is continued some little way into the Fallopian tubes, more especially, on that side where the corpus luteum has been formed; it is perforated at the points where the Fallopian tubes enter, as well as at the os uteri, a fact which is beautifully shown in Dr. Hunter's last plate: but this does not continue long, for, as Mr. John Hunter observes, the inferiour opening becomes closed in the first month, and, according to Lobstein's observations, the openings of the Fallopian tubes are closed after the second month. "Where the decidua reflexa is beginning to pa.s.s over the chorion, there is, at an early period of pregnancy, an angle formed between it and the decidua, which lines the uterus; and here the decidua is often extremely thin and perforated with small openings so as to look like a piece of lace.

"In proportion as pregnancy advances, the decidua reflexa becomes gradually thinner and thinner, so that at the fourth month it forms an extremely fine layer covering the chorion; it comes at the same time more and more closely in contact with the decidua, which lines that part of the uterus to which the placenta is not fixed, till at length they adhere together."[20] That portion of the decidua which pa.s.ses between the placenta and uterus during the latter half of gestation, is called the _placental decidua_, the description of which will be given with that of the placenta.

To Dr. W. Hunter are we indebted for the first correct description of the decidua; indeed, so excellent is it, that the membrane has been called after him, the _decidua of Hunter_. Although he was the undoubted discoverer of the reflexa, the existence of the decidua was distinctly noticed by Burton, in 1751. In stating the _post mortem_ examination of a woman, who died undelivered at the full time of pregnancy, he says, "Upon wiping the inside of the uterus very gently with a sponge, there seemed to be pieces of a very tender thin transparent membrane adhering to it in such parts of the uterus where the placenta did not stick to it; but as the womb was somewhat corrupted, and the membrane so very tender, we could not raise any bulk of it so as to be certain what it was." (Burton's _Midwifery_.)

The decidua seems chiefly intended to form the maternal part of the placenta: (see _Placenta_:) hence in all those quadrupeds when the maternal part of the placenta is permanently appended to the internal surface of the uterus, no decidua is found.

Having described the maternal membranes of the ovum, we come now to the membranes which form the parietes of the ovum. These are called the _foetal membranes_, for they are essentially connected with the origin of the foetus itself. They are the _chorion_ and the _amnion_; besides which, there are two others that require notice, viz. the _vesicula umbilicalis_ and _allantois_.

_Chorion._ The chorion is the proper covering of the ovum, and corresponds to the membrane lining the sh.e.l.l of an egg, in oviparous animals. It is a thin and transparent membrane, and presents on its external surface a ragged tufted appearance, being covered externally with groups of arborescent villous processes, which after a time unite into trunks to form the umbilical vessels, which, according to Lobstein's observations, are merely veins during the early period of gestation. These loose tufts of venous radicles appear to absorb nourishment for the ovum, much in the same manner as the roots of a plant. Although the chorion is so thin and transparent, it consists nevertheless of two laminae or layers, between which the villi, which produce this s.h.a.ggy appearance, take their course.

Although the chorion on its external surface is nothing but a net-work of villi, which in process of time become vascular, anatomists have been unable to detect blood-vessels in the structure of the membrane itself.

Its vascularity, however, has been a.s.serted chiefly on the ground of the known vascularity of the decidua, it being supposed that the vessels of the decidua penetrate into the chorion. The chorion, however, belongs so essentially and exclusively to the foetus, that it appears extremely improbable that any maternal vessels should ramify in its structure for the purposes of its nourishment and growth, and the more so when we reflect that the nutrition of the foetus itself at this early period is obtained in so different a manner. It is, moreover, extremely difficult to distinguish between the venous absorbing radicles of the chorion, which form the early rudiments of the umbilical vessels, and any vessels which may take their course in the structure of the membrane itself; and the more we consider the relation between the chorion and the decidua, the less are we inclined to accept Meckel's explanation of the vascularity of the chorion, viz. that the vessels of the decidua have the same relation to those of the chorion as the blood-vessels of the maternal part of the placenta have to those of the foetal part.

Neither nerves nor lymphatics have been discovered in the structure of the chorion, unless, indeed, those white filaments, which are observed here and there about the edge of the placenta, perform the office of lymphatics. This has been hinted at by Dr. Hunter, where he says, "these are the remains of those s.h.a.ggy vessels which shoot out from the chorion in a young conception, and give the appearance of the ovum being altogether surrounded by the placenta at that time. With a magnifying gla.s.s, they appear to be transparent ramifying vessels, which run in corresponding furrows upon the internal surface of the decidua, and a good deal resemble lymphatics." (W. Hunter, _op. cit._ p. 53.)

The chorion undergoes various changes during the different periods of pregnancy, and forms a very important part of the physiology of utero-gestation. Its thickness, which in the earlier months of pregnancy is more considerable than afterwards, at this period is uniform in every part of the ovum: its external surface covered with those villous prolongations which have already been alluded to. In the second month of pregnancy these become larger, and much more arborescent; after the third month a considerable portion of them gradually disappears, generally from below upwards, so that the greater part of its external surface becomes nearly smooth, except at that point where the umbilical cord has its origin, at which spot the villous prolongations become more developed, and unite to form the umbilical vessels. This part of the chorion, together with the corresponding portion of the membrana decidua, forms a flat circular ma.s.s, which at the end of pregnancy covers nearly one-third of the surface of the ovum, and const.i.tutes the placenta or after-birth. At this point the chorion, which forms its inner surface, is considerably thicker than elsewhere.

At the commencement of pregnancy the chorion is but loosely connected with the decidua, but by degrees it becomes so closely connected by fibres, which are the remains of the little vascular prolongations, especially where these two membranes combine to form the placenta, that in the latter months of pregnancy, they can scarcely, if at all, be separated.

For the more minute consideration of the formation, development, and functions of the chorion, we must refer to the description of the placenta and foetus.

_Amnion._ The amnion is the inner membrane of the ovum. It is transparent, and of great tenuity, "yet its texture is firm, so as to resist laceration much more than the other membranes." (W. Hunter, _op. cit._ p. 50.) It is loosely connected with the chorion on its external surface, except when this membrane unites with the decidua to form the placenta at which spot it adheres to the chorion much more firmly. Its inner surface, which is in immediate contact with the liquor amnii, is very smooth; whereas externally, from being connected with the chorion by an exceedingly fine layer of cellular tissue, its surface is not so smooth. Dr. W. Hunter considers that this intervening tissue, is a gelatinous substance: it seems, however, to possess too much elasticity for such a structure; and, from the reticular appearance which it generally presents upon the membranes to which it adheres, we are inclined to adopt the opinion of Meckel in considering it cellular. "In the very early state of an ovum the amnium forms a bag, which is a good deal smaller than the chorion, and, therefore, is not in contact with it." (_Ibid._ p. 75:) hence, therefore, a s.p.a.ce is formed between the two membranes which is filled with a fluid called the _liquor amnii spurius_, or more correctly the _liquor allantoidis_. "In the course of some weeks, however, it comes nearly into contact with the chorion, and through the greater part of pregnancy the two membranes are pretty closely applied to each other." (_Ibid._) Lobstein, in his admirable _Essai sur la Nutrition du Foetus_, observes, that the membranes continues separate from each other so late as the third and fourth month. Cases every now and then occur where a considerable quant.i.ty of fluid is found between the chorion and amnion in labour at the full period of pregnancy.