A System of Midwifery Part 14

CHAPTER III.

MECHANISM OF PARTURITION.

_Cranial presentations--first and second positions.--Face presentations--first and second positions.--Nates presentations._

If we were asked to point out the basis on which the principles of practical midwifery should be founded, we would answer, on an accurate knowledge of the manner in which the child presents, and pa.s.ses through the pelvis and soft parts during labour. In confirmation of this remark, we may observe, that almost every great improvement in midwifery practice which has taken place during the last century, has resulted from farther investigation into this difficult field of inquiry, and from the gradual addition of new facts to our knowledge respecting this interesting process.

Unless a pract.i.tioner be thoroughly acquainted with every step in the mechanism of a natural labour, how can he be expected to understand and detect with certainty any deviation from its usual course, still less make use of those means which may be required under the particular circ.u.mstances of the case; and yet, strange to say, there are few subjects which, generally speaking, have excited so little attention, and upon which such incorrect opinions have prevailed even up to the present time.

The investigation is confessedly one of considerable difficulty, and as it was more easy to calculate how the head ought to pa.s.s in this or that position through the pelvis than to ascertain how it really did pa.s.s, ingenuity has been taxed, and theories have been invented, and positions of the child without number have been described, which have never existed in nature, and which have only added to the difficulty and perplexity of the subject.

We consider that to form an accurate diagnosis in these cases, requires the highest perfection of the _tactus eruditus_, which can only be acquired by long practice and patient observation: and it is chiefly from this circ.u.mstance that we can explain why such gross errors and vague notions should have existed about a process of every day occurrence, and why, with but few exceptions, they should have been transmitted from one author to another even up to the present time. In the last century, when it was so much the fashion to resolve every physiological process into a mathematical problem, it was scarcely deemed necessary to spend much time in actual observation and examination; the proportions between the head and pelvis were ascertained, their angles were measured, and their curves determined, and from these data it was inferred, what must be the course which nature would follow; few attempted the slow but surer method of ascertaining by patient research the real facts connected with the process of parturition.

When the long axis of the child's body corresponds with that of the uterus, the child (provided the pa.s.sages are normal) can be born in that position: it matters little, as far as the labour is concerned, which extremity of the child presents, so long as this is the case; but where the long axis of its body does not correspond with that of the uterus, the child must evidently lie more or less across, and will present with the arm or shoulder, a position in which it cannot be born. In stating this, we wish it to be understood, that we merely refer to the full grown living foetus, and not to one which is premature, or which has been some time dead in the uterus, as these follow no rule whatever, hence the positions of the child at the commencement of labour resolve themselves into two divisions, viz. where the median line of the child's body is parallel with that of the uterus, and where it is not; the first we shall call _natural_, the second _faulty_, presentations of the child. A description of the natural presentations will form the contents of the present chapter.

The reader will almost antic.i.p.ate us when we state, that the natural presentations consist of two cla.s.ses, those where the cephalic, and those where the pelvic end of the child presents; in the first case, it will be a presentation of the cranium or of the face; in the second, of the nates, knees, or feet.[77]

_Cranial presentations._ The presentation of the cranium, (or _vertex_, as it has been improperly called,) is of by far the most frequent occurrence; thus, for instance, of 4042 children which were born in the lying-in hospital, at Heidelberg, 3834 presented with the head; of these the 3795 with the cranium, and 39 with the face: in either case, whether it be a presentation of the cranium or of the face, it will be either with the right or the left side more or less foremost; the former, from its greater frequency, has been called the first position of the cranium or face, the latter the second position.

_First cranial position._ It will be recollected we have stated, that the os uteri at the end of pregnancy is turned obliquely backwards, corresponding to the upper part of the hollow of the sacrum. If we examine during the first stage of labour, when it is just dilated sufficiently to allow the finger to pa.s.s, we shall feel the sagittal suture of the head running across it, dividing it into two unequal portions, the os uteri itself corresponding nearly to the middle of this suture. If the os uteri be sufficiently dilated to let us trace its course, we shall find that it corresponds more or less to the direction of the right oblique diameter, viz. that it runs from the right and backwards, obliquely forwards, and to the left. If we follow it with our finger in this last-mentioned direction, we come to a spot where it divides into or meets two other sutures; these are the right and left lambdoidal sutures, and beyond them is the hard convex occiput, the point where they meet being the posterior or occipital fontanelle. If we trace our finger along the suture in the other direction, viz. backwards and to the right, we shall come to a four cornered s.p.a.ce, where four sutures meet at right angles to each other; these are the sagittal, the frontal, and right and left coronal sutures; the open s.p.a.ce itself is the great or anterior fontanelle.

That part of the head which lies lowest or deepest in the pelvis, and which the finger first touches upon when introduced along the v.a.g.i.n.a, is the right parietal protuberance; and if the os uteri be sufficiently dilated, we distinguish it by its hard and conical feel. In primiparae, where the head usually is deep in the pelvis at the commencement of labour, and where the anterior and inferior segment of the uterus is closely stretched over it, the parietal protuberance may be felt through this part. Hence, then, the first position of the cranium, (or more correctly speaking, parietal bone,) is marked by the following characters: the sagittal suture crosses the os uteri, and runs parallel with the right oblique diameter of the pelvis: the vertex is therefore turned towards the upper part of the hollow of the sacrum, the posterior fontanelle forwards and to the left: the right perietal protuberance, therefore, is necessarily that part which is deepest in the pelvis; and the perpendicular diameter of the head, instead of corresponding to the axis of the pelvic brim, runs in an oblique direction upwards and forwards.

If the head at this early stage of labour be high up in the pelvis, viz.

has scarcely entered the brim, as is frequently the case in multiparae, the sagittal suture approaches in its direction to that of the transverse diameter, or to one between the transverse and oblique diameters, the posterior fontanelle corresponding to about the left acetabulum. The higher the head is in the pelvis, the nearer does its greater diameter correspond to the transverse one of the pelvis: the more oblique also is its perpendicular diameter, from which reason the right ear at this time can usually be felt without difficulty behind the pubic bones. Sometimes both fontanelles can be reached with equal ease; most frequently the posterior one is lowest, but occasionally the reverse is the case, and it is the anterior fontanelle, without, however, at all influencing the progress of the labour.

As the head advances through the brim and begins to enter the cavity of the pelvis, the sagittal suture corresponds more closely with the right oblique diameter, so that now the posterior fontanelle is turned towards the left foramen ovale, and as it approaches the outlet of the pelvis, the occiput advances still more forwards, although the head entirely quits its oblique position. At this stage of the labour, the fontanelles can usually be again reached with equal facility, and we find the anterior one corresponding to the right sacro-iliac synchondrosis, the occiput is completely behind the left descending ramus of the p.u.b.es, the right lambdoidal suture running parallel with it. Owing to this slight change in the position of the head, the occiput having advanced somewhat forwards, we no longer feel the right parietal protuberance to be lowest and in the centre of the pelvis, but the finger now touches upon the posterior and superior quarter of the right parietal bone, for this is the part of the head which first comes under the pubic arch, and first enters the external pa.s.sages.

If there be but little liquor amnii, or the membranes have been ruptured prematurely: if the head be firmly pressed against the os uteri, and we examine when it is not more than two-thirds dilated, we feel a puffy oedematous swelling upon that part of the head which corresponds to the os uteri. This will therefore be found to be situated upon the sagittal suture, nearly equidistant from the anterior and posterior fontanelles; it arises from the circulation in the scalp being obstructed by the pressure of the os uteri upon the head. If the remaining portion of the labour be rapidly completed, this will be the situation of the swelling with which the cranium is born; if, however, it follows a more gradual course, and the head pa.s.ses slowly through the os uteri into the v.a.g.i.n.a, as it thus advances deeper into the pelvis, and alters its position more or less, the swelling upon the sagittal suture disappears in part, and forms on that portion of the head which is advancing under the pubic arch, and is now tightly encircled by the external pa.s.sage: we shall, therefore, find that this second swelling is situated upon the posterior and superior quarter of the right parietal bone, and this is precisely the situation of the swelling of the head, which the child is usually born with.

From these facts we may deduce the following simple law respecting the mechanism of parturition, where the head presents: viz. that the head enters, pa.s.ses through, and emerges from, the pelvis obliquely; and this is the case not only as to its transverse diameter, but also as to the axis of its brim; the side of the head being always lowest or deepest in the pelvis. This shows the beautiful mechanism of the process, for, on account of its oblique position, there is no moment during the whole labour at which the greatest breadth (still less length) of the head is occupying any of the pelvic diameters; even at the last, when the head is pa.s.sing under the pubic arch, the complete obliquity of its position, in order that it should take up the least possible room, is very remarkable; for the ring of soft parts, by which the head is now encircled, pa.s.ses obliquely across it, running close behind the left, and before the right parietal protuberance. The head never advances with the occiput, forwards, under the pubic arch, as is stated in works on midwifery, still less with the sagittal suture parallel to the antero-posterior diameter of the pelvis; for the direction of the right lambdoidal suture, as also of the posterior fontanelle, and the position of the cranial swelling, or _caput succedaneum_, as it has been called, completely prove the inaccuracy of such a theory, the sagittal suture crosses the left labium at an acute angle, the right lambdoidal suture being parallel with the left descending ramus of the ischium.

Not less incorrect is the theory (for we can call it nothing else) of the head presenting with the vertex, and turning with its long diameter, from the oblique, into the antero-posterior or conjugate diameter, and the face into the hollow of the sacrum, for it is disproved by all the above-mentioned facts, which careful examination during labour puts us in possession of. When the head is born, the face looks backwards and to the right, viz. to the back part of the mother's right thigh, for the shoulders are by this time pa.s.sing through the pelvis in its left oblique diameter, the right shoulder being forwards and to the right, and lowest in the pelvis: it is also that which is first expelled.

Such is the manner in which the head presents in the first or most common position: a slight modification of it is occasionally observed during the early stages of labour, without influencing the favourable character of its progress: the head at first is in the left oblique diameter of the pelvis, the occiput towards the left sacro-iliac synchondrosis, the anterior fontanelle towards the right acetabulum; but as the labour advances, the head turns, so that the occiput corresponds to the left acetabulum, the anterior fontanelle being turned towards the right sacro-iliac synchondrosis, the sagittal suture running parallel with the right oblique diameter of the pelvis. This peculiar commencement of the labour is probably not detected so frequently as it really occurs, owing to its changing into the common position at so early a period.

_Second position of the cranium._ The other or second position of the cranium is, where the _left_ side of the head presents. It is, in fact, merely the reverse of the one just described: the sagittal suture crosses the os uteri at the beginning of labour, as in the former case, only now the posterior fontanelle is turned to the right instead of to the left; it is the _left_ parietal protuberance which is deepest in the pelvis, and which the finger first touches upon. As the labour advances, and the head approaches the pelvic outlet, it is the posterior and superior quarter of the _left_ parietal bone which first enters the v.a.g.i.n.a and protrudes through the os externum, and upon which the swelling of the scalp or _caput succedaneum_ is situated.

The chief peculiarity is, that the change, which we noticed in the first position as an occasional occurrence at the beginning of labour, is in this case the regular commencement of it. In the second cranial position, the head at the beginning of labour, with very few exceptions, is always with its long diameter parallel with the right oblique diameter of the pelvis, the posterior fontanelle turned towards the right sacro-iliac synchondrosis, the anterior one towards the left foramen ovale. During the early periods of labour, when the head is pa.s.sing through the brim, both fontanelles may be reached; and, generally speaking, the posterior one with greater ease, from its being usually somewhat the lower; but as labour advances, and the head has fairly engaged in the pelvic cavity, they may both be reached with equal ease, the anterior fontanelle still corresponding to the left foramen ovale, or rather to the descending ramus of the left pubic bone. "As soon as the head experiences the resistance which the inferior part of the pelvic cavity opposes to it, or, in other words, the oblique surface which is formed by the lower end of the sacrum, the os coccygis, the ischiadic ligaments, &c. by which it is compelled to move from its position backwards in a direction forward, it turns by degrees with its greater diameter into the left oblique diameter of the pelvic cavity, viz. the posterior fontanelle is directed to the right foramen ovale, and as the head approaches nearer and nearer to the inferior aperture, it is the posterior and superior quarter of the left parietal bone which is felt in the cavity of the pelvis opposite to the pubic arch, so that when the point of the finger is introduced under and almost perpendicular to the symphysis pubis, it touches nearly the middle of the posterior and superior quarter of the left parietal bone: and this is precisely the part, as the head advances farther, which first distends the l.a.b.i.a, with which the head first enters the external pa.s.sages, and the spot upon which the swelling of the integuments forms itself." (Naegele, _Mechanism of Parturition_, transl.)

The manner in which this change in the position of the head takes place, varies a good deal in different labours: in primiparae it usually takes place slowly, and requires several pains before it is completed; as the pain comes on, the posterior fontanelle, which was backwards and to the right, now advances more forward and comes more within reach; the anterior fontanelle, which was towards the left foramen ovale, retreats, so that when the pain has reached its maximum the head will for a moment be felt in the transverse diameter of the pelvis, and again resumes its former position as the pain goes off: with the recurrence of each pain there is a repet.i.tion of this screw-like motion, but by degrees the head not only pa.s.ses from the right oblique into the transverse diameter, but from the transverse into the left oblique, so that at length the anterior fontanelle corresponds to the left sacro-iliac synchondrosis, and the posterior one to the right foramen ovale.

In women who have already had children, the whole change is frequently effected during one pain, so that the head, which but a few minutes previously was presenting in what is called the third position of the German schools, will now be found to be in the second.

It is to the celebrated Naegele of Heidelberg that we are indebted for having first pointed out the uniform occurrence of this change in the second position. From his extensive and accurate observations, confirmed since by ourselves, as well as by many others, the head presents with the occiput _originally_ forwards and to the right very rarely, but pa.s.ses into this position during the course of labour. No one has ever described the mechanism of parturition so minutely and correctly; and the value of his investigations is the more enhanced, when we recollect what erroneous notions have prevailed upon this important subject up to the present time.

"In the former part of my practice," says this distinguished obstetrician, "not knowing that the head made this turn, I always concluded that my examinations in the early part of labour were incorrect, and was very uneasy that I did not find it all exactly as the books described, and attributed my want of success in ascertaining the position to my own awkwardness. At length in a private case, in which I was much interested, I again felt what I thought was the anterior fontanelle towards the left foramen ovale; and circ.u.mstances occurring which rendered it necessary to apply the forceps and terminate the labour, I found that the head had been actually in the position which I imagined I had felt. Since this time I have, in many cases, sat by the bed-side during the whole labour, with my finger upon the head, and thus come at the truth." (_MS. Lectures._)

The very circ.u.mstance of this change in the position of the occiput from the sacro-iliac synchondrosis to the foramen ovale of the same side, is of itself quite sufficient to mislead; nor is it to be wondered at that it should have been so long unnoticed, when we recollect how difficult the examination is at this early stage of labour, and how few give themselves the trouble to attain that degree of dexterity and tact, which, even under the most favourable circ.u.mstances, is required for this species of investigation.

The diagnosis of the sutures and fontanelles may be rendered more difficult by other circ.u.mstances: when there is a large quant.i.ty of liquor amnii between the head and membranes, it renders the diagnosis exceedingly obscure in the early part of labour. In some cases the cranial bones are remarkably thin and yielding, and communicate a sensation to the finger as if it were touching a fontanelle; in others, the sutures run an irregular course, and form ossa triquetra, &c. which may easily mislead. We may also notice the changes, already mentioned, which are produced by the death of the child, and the various congenital anormalities of hydrocephalus, acephalus, &c. &c. In some cases the sagittal suture is continued backwards through the occipital bone, dividing it into two equal portions, and thus making the posterior fontanelle four cornered, and not to be distinguished from the anterior. Nor is it always easy to distinguish the posterior from the anterior fontanelle under more normal and favourable circ.u.mstances; for it would be hazardous to conclude that it is the posterior fontanelle merely because we feel three sutures meeting together, as it may possibly be the anterior one, and we are not able to reach the sagittal suture beyond. In this case we may ascertain which it is by the following rule: if it be the posterior fontanelle in the first position we shall feel a suture running more or less forwards (the right lambdoidal,) but none backwards; but if it be the anterior fontanelle forwards and to the left, we shall also feel a suture (the right coronal) running backwards. Lastly, in the second cranial position the face when born turns to the posterior surface of the mother's left thigh.

Such are the two positions in which the head presents during labour, and such is the manner in which it pa.s.ses through the pelvis and external pa.s.sages. Slight deviations do occasionally take place, the chief of which is, that the head in the second position does not always make the quarter of a turn as above described, but comes out with the anterior fontanelle forwards and to the left: this is by no means of common occurrence, and, as far as we have observed, increases the difficulty of labour very little.

_Face presentations._ The face, like the cranium, may present in two ways, either with its right or left side forwards. The former is the most frequent occurrence, and bears a striking a.n.a.logy to the first cranial position; indeed, we cannot too strongly impress upon the minds of our readers the advantages of accurately knowing the different features of the two cranial positions just described; for by this means the positions of the face will be rendered much more simple and easy of comprehension.

Whether the right or the left side of the face presents (first or second facial position,) the root of the nose crosses the os uteri exactly in the same manner as the sagittal suture does in the two cranial positions; the chin is turned to the right acetabulum, and as the face descends through the pelvis during the progress of the labour, the chin moves somewhat more forwards, as the occiput does in the cranial positions.

At an early stage of labour the right eye and zygoma is that part of the face which is lowest in the pelvis, and which the finger first touches upon during examination, precisely as it was the right parietal protuberance in the first cranial position; and as in this case the caput succedaneum was situated upon the posterior and superior quarter of the right parietal bone, so here the livid bruise-like swelling, which the face brings with it into the world, is situated upon the right cheek, this part being the first which presses through the os externum; the chin pa.s.ses under the right branch of the pubic arch, as the occiput in the first cranial position does under the left, the face during the whole process preserving a strictly oblique position, both as to the transverse diameter and axis of the pelvis.[78]

_Second position of the face._ The second position of the face is merely the reverse of the first: it is now the left side which is turned forwards, the left eye and zygomatic process being those parts which are lowest in the pelvis; the chin is turned to the left side and somewhat forward, and advances towards the left foramen ovale during the farther progress of the labour. As the face approaches the inferior aperture of the pelvis, it is the left cheek which first enters the os externum, and upon which the swelling is situated: likewise the chin pa.s.ses beneath the left branch of the pubic arch.

It has been supposed by some authors, and we think correctly that the majority (if not all) of face presentations are originally cranial presentations: if this be the case, we can easily understand why the right side of the face presents more frequently than the left, for if the head in the first cranial position moves round upon its transverse diameter, and thus allows the face to turn downwards, we shall immediately have a first position of the face. We are the more inclined to adopt this opinion, not only from the greater number of cases where the right side of the face presents, but also from our having more than once met with cases where so long as the head of the child was moveable above the brim, the presentation was midway between one of the cranium, and of the face. On one side of the pelvis we could feel the anterior fontanelle; on the other we could, with some difficulty, reach the orbital process of the frontal bone: as the pains increased, and the head advanced lower, the side of the face came more within reach; so that by the time it had fairly entered the cavity of the pelvis, it had become a complete presentation of the face.[79]

We distinguish the face by the bridge of the nose, which from its crossing the os uteri may be detected at a very early period of labour: it is far better than the eye, for not only is this liable to mislead us in our examination, but it may also receive injury from the finger. Nor is the malar bone a guide, for this might easily be mistaken for the tuberosity of the ischium, or even for the shoulder. The nose not only tells us that the face is presenting but also in which position, for at one end we shall feel the soft cushiony extremity of it, at the other we shall reach the broad hard expanse of the forehead.

It was not until nearly the end of the last century that presentations of the face ceased to be accounted unnatural, and impossible to be terminated by natural means. Although the fact had been pointed out by Portal so early as 1685, that these presentations were very little removed from the usual one, it seems to have excited but little attention until the time of Deleurye in 1770. "I have," says Portal, "delivered several women whose children came with the face foremost, and always without any great difficulty, it being only observed, _that in such cases no violence must be used, but nature be left to its own course; which done, there is no danger either of mother or child_." (Portal's _Midwifery_, transl. obs.

66:) La Motte in 1721, although so accurate an observer, could not divest himself of the general opinion that these were unfavourable positions, even although the face was usually expelled by the natural efforts, after he had fruitlessly endeavoured to rectify it, and although he himself confesses never to have "seen any that had not done well."

Giffard has recorded two cases of face presentation (_Cases in Midwifery_, 1734, p. 59, 443.,) both of which he delivered by his extractor, which was one of the early forms of midwifery forceps; and in both, although the labour had lasted some time, the child was alive. He describes the position of the face in the second case, the chin being turned towards the right side. The only practical observation which he makes is, that turning is very difficult where the "waters are gone off, and the uterus closely envelopes the child." This is probably given as an explanation for his deviating from the usual practice of turning in these cases. Deleurye in supporting Portal's views observes, "one daily sees similar labours terminate naturally: it is true they are somewhat longer, but they terminate without the aid of art." (_Traite des Accouchemens_, 1770, -- 736.)

Lastly, the celebrated Boer of Vienna (1793) placed the matter in a still more decided point of view when he a.s.serted, that "face presentations being merely a rare form of natural labour, should be left to be completed by the natural efforts, since neither the mothers nor their children were exposed to any more danger in this form of labour than they were in the most usual forms of all." Having charge of the great lying-in hospital of Vienna, Boer had ample means of ascertaining the most accurate results on all points of practical midwifery, and his observations on labours where the face presented, are, therefore, peculiarly interesting, and tend strongly to contradict the prevailing opinion respecting the difficulty and danger of these presentations.

"Of eighty cases of face presentations which have occurred during a period of some years, and which I have myself observed and noted down, there were three, or at the most four, where the children were born dead. None of the patients suffered in the slightest degree from any of these labours; and, except one case, all were left entirely to nature: in one case only, on account of the weakness of the pains and doubtful character of the symptoms, I deemed it necessary to terminate the labour by the forceps." (Boer's _Naturliche Geburtshulfe_, erstes buch, p. 137.) In spite of this valuable practical fact, supported by experience on so great a scale, the opinion that face presentations were preternatural, continued to prevail upon the Continent, being supported by the authority of Baudelocque and Osiander. A similarly unfavourable opinion was entertained by Dr. Smellie in this country, although Dr. W. Hunter, in his lectures delivered prior to the publication of his plates on the gravid uterus (and, therefore, at an early date,) states, "in this case I do not turn the head round in order to deliver, but nineteen times in twenty leave it to itself to come as it will." (W. Hunter, _MS. Lectures_.)

Dr. R. W. Johnson, who dedicated his _New System of Midwifery_, &c. to Dr.

W. Hunter and others, in 1769, and probably attended his lectures, expresses a similar opinion, and says, that in these cases "nature herself will do the work." (p. 267.) Dr. Alexander Hamilton, in 1784, also speaks favourably of these presentations. "The head will, however, in most cases, advance in that position by the force of the natural pains, though the delivery will be more slow or painful." (_Outlines of the Theory and Practice of Midwifery._)

Farther experience has shown that, so long as the pelvis is of the natural size, the head can be born in this position without peculiar difficulty, the soft parts usually require a little more dilatation than where the cranium presents, and, therefore, this stage of the labour is generally somewhat slower. Although presentations of the face are not so favourable for the child as those of the cranium, they stand next to them in point of safety. Where the cranium presents, a slight misproportion between the head and pelvis produces little or no increase of difficulty to the pa.s.sage of the child; but under similar circ.u.mstances, where the face presents, the difficulty may become very serious, for if the labour is prolonged, "the brain and vessels of the neck," observes Smellie, "will be so much compressed and obstructed as to destroy the child." (Explanation to table 25.) A similar view has been given by Dr. Denman, and still more recently by Professor Chaussier, of Paris, and Professor Naegele; the two latter authorities examined the brain in several still-born children where the face had presented, and invariably found the cerebral vessels gorged with blood.

The presenting side of the face when born is frightfully distorted by the livid swelling above-mentioned; the mouth is pulled to one side and upwards; the angle of the eye is drawn downwards, and the corresponding ala of the nose scarcely discernible amid the purple ma.s.s of tumefaction: the less this is meddled with the better, for in the course of a day or two the parts will have returned to their condition; whereas, if friction or hot poultices, &c., be used, ulceration may be the result, and produce considerable disfigurement.[80]

_Nates presentations._ "After the presentations of the cranium those of the nates are the most frequent in point of occurrence, and also the most natural," says the celebrated Boer, in the work already quoted. Under the term _nates_ presentations, we include those of the knees and feet, as these latter presentations can only be looked upon as modifications of the former. Professor Naegele, jun., in his new edition of the admirable essay upon the mechanism of labour, published by his father, in Meckel's _Archiv. fur die Physiologie_, has very properly brought these different positions under one head, viz. "positions of the pelvic extremity of the child:" as, however, we possess no word in English to express this, we shall attain the same object by considering knee and footling births as mere modifications of breech presentations.

"As regards the relative situation of the limbs to the body of the child, the position is the same as in the two genera of head presentations above described, viz. the knees are usually drawn up to the abdomen, the feet close to the nates, so that not unfrequently they may both be felt together at the beginning of labour, and afterwards descend into the pelvis and are born together. Sometimes the feet (or perhaps only one foot) are felt higher above the brim than the nates; in which case, as the nates descend they rise, and are turned upon the abdomen and breast of the child, and descend with these parts as labour advances. Frequently it is the reverse: the feet are somewhat lower than the nates; they are felt in the os uteri at the beginning of labour, and descend before them as labour advances. It is rare that the knees come down before the nates during the farther progress of labour, and it is not probable that they are ever found alone in the os uteri at the commencement of it." (H. F. Naegele, _Mechanismus der Geburt_, 1838, p. 57.)

The nates may present in two ways, either with the back of the child forwards, or with its abdomen forwards: of these the former occurs most frequently; thus of 161 cases which were accurately ascertained at the lying-in hospital of Heidelburg, 121 were observed with the back of the child forwards, and 40 with it backwards: in either of these positions the transverse diameter of the child's pelvis always corresponds to one or other of the oblique diameters.

"Labours with the nates or feet presenting, follow certain laws quite as much as those where the head presents, only that one more frequently sees deviations from them, both with respect to the manner in which the child presents at the time of labour, and its pa.s.sage through the pelvis; but where, under a proper state of the other requisites for healthy parturition, no prejudicial result occurs." (Naegele, _on the Mechanism of Parturition_, transl. -- 19. p. 128.) "In every case, whether the nates have at first a completely transverse or oblique direction, they will be always found, on pressing lower into the superior aperture of the pelvis, to have taken an oblique position; and that ischium, which is directed anteriorly, to stand lowest. They pa.s.s through the entrance cavity and outlet of the pelvis in this position, which is oblique, both as to its transverse diameter as well as to its axis."

Thus, if in the first species the left ischium were either originally directed more or less forward, (which is usually the case,) or had taken this direction in pa.s.sing through the superior aperture, the nates descend in this direction into the pelvic cavity, with the left ischium during the whole time standing lowest; and this is the part, during the farther progress of the nates, which first pa.s.ses between the l.a.b.i.a as the os externum dilates. As they advance, and while the left ischium, which is directed forwards and always somewhat to the right, comes completely under the pubic arch and presses against it, the other ischium, which is situated in the opposite direction, and which has to make a much greater circuit, pa.s.ses forwards over the strongly distended perineum, so that, when the pelvis is born, the abdomen of the child will be directed to the inner and posterior surface of the mother's right thigh.

"The rest of the trunk follows in this position, and as the breast approaches the inferior aperture of the pelvis, the shoulders press through its superior aperture in the direction of the left oblique diameter; and during its pa.s.sage (viz. the breast) through the pelvic outlet, the arms and elbows which were pressed against it are born at the some moment. But whilst the shoulders are descending in the above-mentioned oblique position, the head, which during the whole progress of the labour rests with its chin upon the breast, presses into the superior aperture in the direction of the right oblique diameter, (viz. with the forehead corresponding to the right sacro-iliac synchondrosis,) and then into the cavity of the pelvis in the same direction, or one more approaching the conjugate diameter. After this, it presses through the external pa.s.sage and the l.a.b.i.a, in such a manner, that whilst the occiput rests against the os pubis, the point of the chin, followed by the rest of the face, sweeps over the perineum as the head turns on its lateral axis from below upwards.

"But it is sometimes the right ischium, which, in this chief division, is either originally turned forwards, or in the process of time a.s.sumes this direction. In this case the child pa.s.ses through the pelvis in the same manner as before, only with the difference, that the surface of the body takes of course a different position with respect to the pelvic parietes, viz. its anterior surface, which in the former case corresponded to the right side of the pelvis, will be directed to the left, and the head will press through the superior aperture of the pelvis, in the direction of the left oblique diameter (the forehead pa.s.sing before the left sacro-iliac synchondrosis.)"

"As in positions of the cranium, the swelling of the integuments is chiefly met with on that parietal bone which during the pa.s.sage of the head, is situated lowest, and on that spot with which it enters the external pa.s.sage, so in this case the livid coloured swelling appears on that part which, directed forwards, was situated lowest during the pa.s.sage of the nates, and with which the nates were born.

"In the second chief position, viz. with the anterior surface of the child corresponding to the anterior abdominal parietes of the mother, it is chiefly the left ischium which is either originally situated forwards, or takes this direction as the nates sink through the superior aperture of the pelvis, which latter preserve this oblique direction during the farther progress of the labour, both whilst pressing into the pelvic cavity, and when entering the external pa.s.sages.

"If the ischia be already born, the anterior surface of the child turns itself to the right and backwards, either immediately, or as the rest of the trunk advances; but the manner in which the head in this case presses through the entrance cavity and outlet of the pelvis, is the same as has already been described." (Naegele, _op. cit._ p. 128, 130.)