If the sagittal suture should be found to run across from the pubes to the sacrum, instead of from one side to the other, it will then indicate either an occipito pubic, or occipito sacral position, according as the back of the head is behind or before; and this can be readily ascertained by finding either of the fontanelles.
In short, if the relative position, forms, and directions of these openings in the child's head be clearly understood, the position of the head can nearly always be determined by feeling them, as will be evident by referring to our former explanation of them.
Sometimes however, the bones overlap a good deal, from the head being pressed, and then instead of an opening along the top, a seam will be felt. And sometimes, from long continued pressure, a quantity of blood, and watery fluid, will be effused under the scalp, so as to prevent the bone being distinctly touched. But these accidents seldom happen, and with ordinary care and perseverance, need not prevent the position being determined, after a little delay.
The position of other presenting parts is easily ascertained, by feeling for some known point—as the nose, or the face, the depression between the cheeks, or the breech, and so on.
Relative frequency of the different positions.—The most favorable positions, like the most favorable presentations, are also the most frequent. According to Baudelocque, in ten thousand three hundred and twenty-two cases, of head presentation, there were eight thousand five hundred and twenty-two cases when the back of the child's head was on the mother's left side, and towards the front, (or in the left anterior occipito iliac position); one thousand seven hundred and fifty-four when it was on the right side towards the front, (right anterior occipito iliac); twenty-five times to the right side, but towards the Sacrum, (right posterior occipito iliac); and nineteen times on the left, but towards the Sacrum, (left posterior occipito iliac.) Being most frequently with the back of the head towards the front on the left side, as shown in Plate XXVII; next towards the front on the right side; and but seldom towards the Sacrum, or back, on either side. In all these ten thousand cases we do not find a single instance of the head lying from back to front, in the occipito pubic, or occipito sacral positions, commonly called transverse; neither do we find a single instance in fifteen thousand six hundred and fifty-two cases recorded by Madame Lachapelle; which will show how rare such unfortunate positions must be. What this great frequency of one particular position depends upon we do not know—possibly on that cause, previously alluded to, which determines the most frequent presentation.
In the next Chapter, the mechanism of delivery, or the manner in which the child escapes out of the body, as it most frequently occurs, will be fully explained.