perineum, the perineum, while it yields before the descending power, thrusts the occiput firmly upwards against the crown of the pubal arch, as in the first position. The extension or reversion of the head being completed by its expulsion, restitution then follows by carrying the vertex to the right acetabulum, outside, and the face to the left thigh. The left shoulder turns to the right and forward to get under the arch, while the right shoulder goes back to the sacrum, and so the shoulders are delivered; sometimes, however, the pubal shoulder is the first, and sometimes the sacral one is the first to be expelled.

Third Position.-The mechanism of the head, when the vertex presents in the third position, differs from the two just before described, only in the absence of the second act, the act of rotation.

These third positions are very rarely observed; and it is probable that, when they are met with, they depend upon a peculiar form of the superior strait.

I possess some pelves in which the antero-posterior diameter of the superior strait greatly exceeds the length of the transverse or oblique diameters. In such a pelvis it is obvious that the vertex would be more likely to present itself at the pubis than at either acetabulum. In an ordinary conformation of the superior strait, a third position of the vertex presentation is extremely unlikely to occur, since, long before the commencement of the labor, the prominence of the lumbar vertebræ, and the overhanging promontory of the sacrum, would be almost sure to turn off the rounded forehead of the child into the right or left sacro-iliac region; and this the more probably, inasmuch as the oblique being greater than the antero-posterior diameter, it affords an easy and inviting accommodation to the usual oblique mode of engagement. The three positions that have here been spoken of comprise the occipito-anterior positions of the vertex. They are those I have been accustomed to enumerate in the following order, viz: first, second, third; or vertex-left, vertex-right, and vertex-front positions.

We have next to describe the fourth, fifth, and sixth; or foreheadleft, forehead-right, and forehead-front positions of the vertex presentation.

Fourth Position.-In the fourth position, the occipito-frontal diameter crosses the pelvis obliquely, as it does in the first position, with this difference, that its frontal extremity is at the left acetabulum, and its occipital pole at the right sacro-iliac junction. See Fig. 23.

This is a true vertex presentation; and it must not be mistaken for a presentation of the forehead. It is a true vertex presentation, be

cause the chin is close to the breast, and there is no departure; on the

contrary, the flexion is,

Fig. 23.

perhaps, even stronger than in the occipito-anterior positions.

The mechanical form of the pelvis is so miraculously adapted to the wants of the economy in labor, that it has full power, in a major part of these fourth positions, to rotate the vertex from the right sacro

iliac junction to the right acetabulum and thence to the pubal arch; and that without any assistance given by the accoucheur.

It is true that this favorable rotation does sometimes require the aid of the hand, or even of an instrument, as shall be described on the proper occasion. It also occasionally happens that neither the hand alone, nor any instrument can enable the surgeon to bring the vertex round to the front. In such case, it slides into the hollow of the sacrum, and the labor is thenceforward rendered more painful and more difficult. When, in fourth positions, the vertex can rotate first to the acetabulum and then to the arch, the labor is not seriously retarded, and the mechanism thenceforth is the same as has been already treated of and described; but when the posterior fontanel gets into the hollow of the sacrum, and will not suffer rotation, then the flexion must become greater and greater as the fontanel slides down along the point of the

Fig. 24.

sacrum, over the face of the coccyx, and down the mesial line of the perineum, until, having thrust away the perineum 4.10-the occipito-frontal diameter-the vertex slips over the fourchette, and immediately turns over backwards, in strong extension towards the woman's back. This allows the forehead, eyes, nose, mouth, and chin successively to emerge from underneath the crown of the pubal arch, to complete the birth of the head. The annexed figure (24) of a head in an occipito-posterior position shows these truths clearly enough.

Such is the mechanism in all cases of birth in occipito-posterior

positions, failing rotation to the front; and the Student will clearly understand that it must be so, since the length of the line from forehead to vertex is too great to permit it to be otherwise.

Fifth Position.-The fifth position, as in Fig. 25, is that in which the vertex is to the left iliosacral space, and the forehead to the right acetabulum. Here, as in the fourth position, the mechanical form of the pelvis tends to turn the vertex first towards the left acetabulum, and thence to the arch.

Fig. 25.

Sixth Position.-The sixth position finds the vertex at the promontory of the sacrum. Madame Boivin met with only two such positions in 19,614 cases.

I have seen a greater number of sixth positions than were met with by that celebrated midwife, although the labors witnessed by her so greatly exceed in number all that I have seen.

While the facts stated in her tables are to be relied upon for their historic accuracy, her statistical results cannot be admitted as the law of any practitioner's future experience. My own practice, for example, which has been a private practice, has shown me a far greater number of sixth positions than her vast clinical experience, in an immense lying-in hospital, brought to her view. Madame Lachapelle saw no such case.

A case of vertex labor in the sixth position occurred to me this day, of which I made the following note, in order that I might set it down here as a freshly remembered experience.

CASE.-July 8, 1848, 101 A. M. Mrs. E—I—————, Pine street. This is the sixth child; a male, born fifteen minutes ago. The pains commenced moderately, at 4 P. M. yesterday, July 7. Mrs. I. has been in pain at regular intervals all night. I arrived at quarter past nine, one hour since. The os uteri was nearly dilated; membranes unruptured. The anterior fontanel was touched through the membranes just behind the upper half of the symphysis pubis. By a strong pres

sure, I could conduct the index finger along the sagittal suture directly toward the sacrum, until I felt the triangular fontanel, leaving no doubt of the diagnosis. The left shoulder was at the right, and the right shoulder at the left ischium. The occiput was opposite to the top of the third segment of the sacrum; the flexion of the head was strong.

Partly by pressing with my right index the right temple and zygoma towards the right, and partly by pulling with the same finger the right leg of the lambdoidal suture towards the left side of the pelvis and downwards, I converted this sixth into a fifth position. I now discharged the liquor amnii by rupturing the bag of waters. The next pain rotated the vertex to the left acetabulum or first position, whence the vertex came forwards and to the right until it reached the arch, under which it began to extend, and was soon expelled.

During the act of extension and expulsion of the head, and just before the whole head was completely born, an act of restitution commenced; as soon as the head was free, the vertex went round again left-wards to the sacrum, and the chin of the child rested with its under surface upon the front of the pudenda, the face looking upwards.

This happened because the shoulders had not rotated at all, but plunged into the pelvis, the left one at the right, and the right one at the left ischium.

With the next pain the left shoulder came to the arch, and the right one to the sacrum, and so they were delivered. The child was about seven pounds in weight; in good health.

Here, then, was a clearly marked case of sixth position, notwithstanding which, the mechanical force of the pelvis and its strange adaptation to the form of the cranium, permitted me, with very slight assistance, to convert it into a fifth, and then into a first position. This rotation was fortunate for the mother; since, by effecting it, I prevented the necessity of a dilatation equal to the occipito-frontal circumference nearly, and thus rendered necessary a dilatation equal merely to the bi-parietal circumference; the former being nearly fifteen inches, while the latter is not more than twelve inches.

August 4, 1856. I attended a labor last night, in which the child presented in the sixth position. I touched the ossa nasi behind the top of the pubis, yet the pelvis rotated the head, and the vertex came to the front, and was easily born.

Face Presentation.-When the head presents in extension instead of coming down in flexion, we have presentation of the forehead, or of the face. If the extension be moderate, the forehead presents; if it

be very great, the face presents. When the face presents, it always comes down with the chin to one side, and the top of the forehead to

the other side of the pelvis; and afterwards rotates the chin to the pubis or to the sacrum. In the case (Fig. 26), the chin is to the right ischium and the forehead to the left ischium. The natural movement of the mechanism would gradually turn this chin to the front of the pelvis, and the top of the forehead to the sacrum, as in Fig. 27.

In face presentations, the chin must be born first; see Fig. 27. Here observe, that from the chin to the vertex is more than five inches, while there is no diameter five inches long to be found within the true pelvis. Hence, if the mental extremity of the occipito-mental diameter descends into the cavity before the occipital extremity, it must escape first from the outlet in order to allow the occipital extremity to escape last, and vice versa.

There are many cases of face presentations that appear to afford remarkably easy deliveries, and to require no aid from the hand. In all those, however, where assistance is demanded, there is an important doctrine, one that should never be lost sight of in the conduct of the cases. The doctrine is this-Bring the chin to the pubis. The figure may show that, if the chin be brought to the pubis, it will have to sink only an inch, or an inch and a quarter lower than the brim, in order to get below the level of the crown of the arch: as soon as it reaches that point, it comes out beneath the arch, and thus the mental extremity of the occipito-mental diameter begins to be born. When this first step is effected, the whole length of that diameter is soon. expelled, or, in other words, the whole head is born; its occipital extremity being the last portion to emerge from the ostium vaginæ.