2. It is impossible because the blades have not been introduced to the same depth, and the pivot does not correspond to the mortise. Then, say the authorities, we must pull out or push in one of the blades, to bring them to the same level. We are opposed absolutely to this. We must not forget that, in such cases, there is nothing to guide the blade which we are endeavoring to push deeper, and hence we may wound the foetus or the maternal parts. We prefer to withdraw one blade, usually the right, and apply it anew.
3. Locking is not possible because, although pivot and mortise are at the same level, the two blades are in different planes. Here again author ities advise seizing the blades, and by rotating them inversely to bring them into the same plane. (Fig. 85.) We are absolutely opposed, in every sense, to this manceuvre. Either the head is well grasped and locking is easy; or else the head is badly grasped and locking impossible, and then the rule should be to begin over a hundred times, if need be, rather than to use any force. We must not forget that each blade of the forceps is a lever, and that every motion im parted to the handles is communicated, greatly exaggerated, to the extremi ties of the fenestrte. Torsion, however slight at the handles, becomes considerable at the points of the fenestrte, and we might wound the foetus or the mother.
Once locked, we must assure ourselves that the head is well grasped, and grasped alone (without cord, cervix, or limb), and that the instrument firmly holds the head.
The finger in the vagina will assure us of the two first. As for the last, a few tractions on the forceps will tell us of the hold on the head, and the separation of the handles as to whether the head is grasped regularly or not. (Fig. 86.) With Tarnier's forceps, we must gently compress the head with the handles, bring the screw in contact with the handles, turning the more as we expect greater resistance. The traction rods are articulated to the transverse bar, and we proceed to extraction.
fu need now only be delivered by traction on the handles, and delivery will be the easier when we make the head execute by means of the instrument the movements which it would spontaneously make in normal labor. The tractions then must not only engage the head, but must make it traverse the vagina as nearly as possible in the pelvic axis, and in certain posterior positions we must make the head ro tate, in order that, in vertex presentations, the occiput may come under the symphysis, and the chin, in face presentations. Although, if need
be, we can deliver with the occiput posterior in case of vertex presenta tions, we must bring the chin under the symphysis in order to deliver in face presentations.
The tractions, then, must be different according to the elevation of the head.
If it is above or at the superior strait, we must, at the outset, make traction backwards and below, in order to engage the head and bring it below this strait. Unfortunately these tractions can never be sufficiently directed backwards, on account of the perineum against which the for ceps press, and to remedy this Ilubert and Morals devised their forceps, and Tarnier gave to his first model the perinea] curve nearly similar to that in Morals' instrument.
Once the head in the cavity, the tractions should be directed a little more forwards, so that when the head has reached the level of the inferior strait, or when the forceps are there applied at the outset, tractions are nearly horizontal. (Fig. 88.) The head at the vulva, traction is made from below upwarct, that is to say, the forceps are lifted up towards the abdomen of the mother. Here, indeed, traction is nearly useless, the head has simply to be disengaged, and once the occiput under the symphysis, not only must we no longer pull on the forceps, but, with the instrument towards the mother's ab domen, we must firmly hold the head, oppose its too rapid exit, and allow it to issue from the maternal parts but very slowly. (Figs. 89 to 91.) It is not enough, indeed, to sustain the perineum, as is represented in Fig. 89. To prevent its rupture, we must give it time to relax, and if we do not hold back the head enough, the perineum will tear under the sup porting hand. Often, indeed, at this very moment, the woman, against her will, makes violent expulsory efforts, and the head, driven violently outside, tears the perineum notwithstanding the accoucheur's hand. The better plan is to slowly disengage the head, holding it back as much as possible, and completing delivery between the pains, and if the perineum seems too distended and ready to tear, to make a lateral incision, and thus avoid deep laceration.