it, and is often burst and the waters discharged, before the fundus of the womb comes at all to press on the child's breech and push it downwards. But whenever the fundus uteri does begin to compel the child downwards, it can only do so by acting on the pelvic extremity of the spinal column. The cephalic or cervical extremity of this column of course resists the force, and the spine becomes more arched. It is as if one end of a bow were set upon the floor, and the hand resting on the upper end should press it directly downwards in order to bend the bow. The outward thrust of the arch is in this case so great that the ends of the bow strive to retreat to the parallel of the centre of the piece. In the same manner, the cervical end of the spinal arch, attached as it is to the condyles of the occipital bone, will naturally thrust backwards, and thus raise the vertex and depress the chin; or I should rather say (as the head is downwards), it will depress the vertex and raise the chin, forcing it towards the infant's breast, while the vertex, which is the occipital extremity of the occipitomental diameter, descends, as the presenting part. This happens the more readily, as the child's head lies over the pelvic opening, which, so to speak, yawns to receive it.

This bending of the neck, or carrying of the chin to the breast, is a most important act in the mechanism of a labor; it is called the flexion of the head; and when it takes place in due degree, it enables the head to descend into the pelvis with very little obstruction; for the other change, called the rotation of the head, does not take place well if this first step fails. The head of a child at term passes very easily into and through a well-formed pelvis, provided it present certain of its diameters only to the canal. Now the diameter extending from the child's chin to its vertex is 5.5 in many children: but the outlet of the pelvis is nowhere more than four and a half inches, at most. Of course, the child could not be born, should it present such a diameter. Again, the diameter extending from the vertex to the space between the eyebrows, is fully 4.5, and often more than that: but from one ischial tuberosity to the other is but four inches, so that, were the occi pito-frontal diameter of 4.5, to become parallel with this bis-ischiatic diameter of four inches, the head would stop; it could not descend any farther. The vertical diameter of the head is, however, only 3.75, which is smaller than any one of the pelvic diameters; so that no great obstruction can, in any natural labor, be offered by the bones, provided the chin, early in the process, be borne strongly against the breast, so as to make the vertex descend, and cause a considerable dip of the horizontal diameter of the foetal cranium.

Positions. Though I have treated on the subject at p. 85, I shall here recapitulate some remarks on positions, a word which, in Midwifery, refers to a relation existing between a cardinal point on the pelvis and a cardinal point on the child's head. The cardinal point on the pelvis is the acetabulum, or rather the acetabular region. The cardinal point on the child's head is the vertex or posterior fontanel. When these two cardinal points come together, the position is number 1, and the other positions are called 2d, 3d, 4th, 5th, or 6th.

The promontory of the sacrum juts into the superior strait in such a manner as to turn any rounded body off, either to its right or left side, and accordingly, it rarely happens that either the forehead or the vertex can pass down immediately in front of the promontory; but, as there is a sacro-iliac concavity on each side of it, the vertex, or the forehead passes down in this concavity, which gives to the head an oblique direction as to the opening, or plane of the superior strait. The cut, Fig. 77, shows how the intrusion of the promontorium into the outline of the superior strait may serve as a guide to the forehead, compelling it to rest in the right, or in the left sacro-iliac space, as the case may be. The forehead, in a majority of instances, goes to the right of the promontory, or in front of the right sacro-iliac symphysis, while the vertex descends below the brim, opposite to the left acetabulum; not at

Fig. 77.

a fixed point, but either nearer the front of the pelvis, or more posteriorly, as the case may be. Indeed, the child generally is found to bore with its head, so as to turn the vertex now forwards, and now backwards, until at last it becomes fixed in one position, by getting under the arch of the pubis. So common is it to observe the child to descend with the vertex opposite to the left acetabulum, that that is taken or counted as the first position of a vertex presentation; and Baudelocque, whose authority on this subject is much followed in the United States, enumerates a second, third, fourth, fifth, and sixth position, the enumeration or order being founded on the supposed relative frequency of the several sorts, as they are met with in practice.

Thus the most frequent, according to Baudelocque, is the first position, in which the vertex is directed to the left acetabulum, and the forehead to the right sacro-iliac symphysis. Here the two cardinal points come together.

Next in order is the second position, in which the vertex is to the right acetabulum, and the forehead to the left sacro-iliac symphysis.

The third position is that in which the vertex is behind the pubis and the forehead in front of the promontory.

The fourth position is that in which we find the vertex at the right sacro-iliac symphysis and the forehead towards the left acetabulum. The fifth position is that in which the vertex is at the left sacro-iliac symphysis, and the forehead towards the right acetabulum.

And lastly, the sixth position, wherein the vertex is at the promontory and the forehead at the symphysis pubis.

It is doubtless extremely convenient and proper to reduce all the possible modes of vertex presentations to a small, yet sufficiently comprehensive classification; but the reader, and especially the young Student, should remember that all these classifications are human inventions. They are the proposita or the dogmata of different men; and, in fact, it is possible for any presentable part of the head to present itself at any part of the brim. If he should, however, find any difficulty in remembering the order or application of these several positions, let him make use of such an arrangement as the following, which I place before him in this connection, rather than refer him back to an antecedent page.

Beginning with the vertex at the left acetabulum, let him say, vertex left; then, proceeding to the second position, in which the vertex is at the right acetabulum, let him say, vertex right, and so on, for the whole of the six positions, as follows:

Vertex left, vertex right, vertex front. Forehead left, forehead right, forehead front.

If the vertex be at the left acetabulum, the forehead is, of course, at the right sacro-iliac symphysis; if it be at the right acetabulum, the forehead is at the left sacro-iliac junction, and vice versa; for all these six positions are vertex positions. So, if it be forehead left, the ver tex is at the right sacro-iliac joint. If the forehead be to the right, the vertex is near the left sacro-iliac symphysis; if the forehead be front, the vertex is towards the promontory. Hence I repeat, vertex left, vertex right, vertex front; forehead left, forehead right, forehead front. The first three are occipito-anterior positions, and the last three are occipito-posterior positions.

I have ever found this enumeration the easiest one to remember; and, as a real nomenclature of the positions, I prefer it to all others, and recommend it to the Student of Medicine.

Madame Boivin, in her Mémorial sur l'Art des Accouchemens, gives us a table showing the relative frequency of these positions.

In her practice, in 20,517 births, there were 19,584 vertex presentations, of which there were of the

Madame Lachapelle's practice, in 22,243 births, showed that there were 20,698 vertex presentations, of which there were of the

That distinguished obstetrician, Dr. C. F. Nægèle, Professor of Midwifery at Heidelberg, asserts that, while the most ordinary position of the vertex presentation is that in which it is found nearest the left acetabulum, the one next in frequency is the fourth, or forehead left position, and he calls it, therefore, the second, in his enumeration. Dr. Nægèle makes this enumeration of first and second positions at page 114 of his Lehrbuch der Geburtshülfe, &c., and at sect. 264, p. 120, gives his views as to the very ordinary occurrence of fourth positions; and at sect. 267, p. 122, declares that, cæteris paribus, the forehead-left positions are as favorable for the mother, and the child also, as the first or vertex-left positions-the vertex rotating spontaneously from the right sacro-iliac junction to the right acetabulum, and then to the pubal arch.

In a conversation I had with this venerable and most honored professor, at Heidelberg, in 1845, he gave me convincing proofs of the correctness of his opinions of these circumstances.

Indeed, I had kept a register of presentations a few years before, upon learning, through a publication of Dr. N.'s Mechanism of Labor, made by Dr. Edward Rigby, now of London, that the common view, as to the greater frequency of the vertex-right position, was erroneous. I am fully convinced, by my register, and by the course of my clinical experience ever since, that Professor N. is quite correct in his statements; and I venture to assure the medical student that, while he shall surely meet with vertex-left positions more frequently than any others, he shall as surely find the forehead-left positions next in point of frequency.

This is a comfortable doctrine; for, the tyro, who has studied in the books the so-called mechanism of the head in the pelvis, is very likely

to be startled at the first case of forehead-left presentation he shall meet with; but if he now learns that it is a natural position, and the one second in point of frequency, he will not suffer himself to be disturbed by the occurrence; particularly if he remembers Dr. Nægèle's assurances, as above expressed. Dr. N.'s words are: "Die geburtèn bei der zweiten shädellage gehen, unter übrigens ganz gleichen umständen, durchaus ohne grössere Schwierigkeit als die bei der ersten, vor sich, und es hat nicht den allermindesten Einfluss auf die Mütter oder das Kind, ob der Kopf sie in der ersten oder in der zweit en Shädellage zur Geburt stellt."

Dr. Edward Rigby, of London, who was Professor Nægèle's pupil at Heidelberg, translated, some years since, as I stated, a small volume of his worthy teacher's on the mechanism of labor. At p. 36, Dr. N. informs us that, according to his observations during many years, made with the greatest possible care and attention, the fourth position, that in which the occiput is near the right sacro-iliac symphysis, is, after the first, far the most frequent in occurrence of all the head presentations; whereas, he thinks our second position of the vertex occurs very rarely. Out of one hundred labors where the head presented, there were twenty-nine cases of the fourth position; and out of another series of thirty-six labors there were twenty-two of the first, and eleven of the fourth position. The result of his inquiries shows that the fourth is to the first position in frequency, as one is to two and a half.

I am glad to be able to confirm Dr. N.'s statement so far as to say, that I am of opinion, from my own experience and observation, that the fourth position is far more frequently met with, in my own prac tice, than any other except the first. The reader has already seen in the table, that in Madame Boivin's records the relative frequency was 15,693 of the first, 3,682 of the second, and only 109 of the fourth. I am sure that the statistical record will not be borne out by the experience of any reader of the Midwifery Library. Professor Simpson agrees with Dr. N.'s views.

Mechanism.-Let the head enter the pelvis obliquely, the vertex being in the first, or vertex-left position; it is not to be understood that the dip of the horizontal diameter of the head will carry the pos terior fontanel into the centre of the pelvic canal: on the contrary such a dip would be too great; but the vertex, or posterior fontanel, glides down along the ischium, repelled by that bone, and directed by its inclined plane inwards and forwards; so that it describes a spiral line in its descent, and the vertex, which on entering the upper strait was directed to the left, is, without any change of posture of the child's