The posterior blade in position, it should be directed backwards towards to sacro-iliac synchondrosis, and it is thus, in oblique positions, placed t the extremity of the bi-parietal diameter, where it remains fixed. The blade, the anterior, is similarly directed backwards towards the pposite synchondrosis, and then it is placed behind the cotyloid cavity, tat is to say anteriorly, making it traverse the entire lateral half of the elvis. The manoeuvre is accomplished by forcibly depressing the left lade, and carrying it from before backward, towards the anus. (We are )eaking now, be it understood, of oblique positions, where the blades are pplied directly to the right and left.) Velpeau has adopted this method.
B. Baudelocque's supposes that the position of the head always known, and that consequently we know a priori what point of to pelvis corresponds exactly to the bi-parietal diameter of the foetal end, and, therefore, the position which must be assumed by each blade. fn. therefore, places at once one blade in front, and the other behind.
C. Mme. Lachapelle's two methods we have described assess serious disadvantages, and hence Mme. Lachapello has modified tem after the following manner, which has been adopted by all French 3coacheurs and numerous foreign: " If the blades are to be placed diagonally, one behind and to the side, the other in front and to the opposite side, it suffices to push the poste rior blade directly along the sacro-sciatic ligament; nothing will stop it. I can then manage the other easier, by beginning with it. I hold it like a pen inclined over the groin, opposed to the side of introduction, and I insinuate the point of the fenestra in front of the sacro-sciatic ligament, and, as it enters, I depress the handle between the thighs till it lies below the anus. In this way, I make the point of the fenestra describe a spiral, which is guided perfectly by the fingers in the vagina. The fenestra is thus carried in front and above. The movement is rapid, and painless. It differs from Levret's method in that here it is the extremity, while in his method it is the border of the fenestra which leads the way. I ought to add that the spiral movement is only easy when the head is below the superior strait; when it is above, this movement is no longer possible, and we can only introduce it, if at all, after Levret's method." Above the superior strait, indeed, the two blades are applied to the sides of the pelvis, and the head is grasped no longer regularly, but, as far as possible, diagonally from brow to occiput. The greater or less separation
of the handles tells us that the head has been seized regularly or irregu larly.
8. The Blades must never be forcibly the direction given to the blades is good and regular, it is surprising with what ease they penetrate. We should always proceed with the utmost gentleness, and be in no hurry; any resistance indicates a bad direction given to the instrument. Obstacles may depend on folds in the vagina or on the foetal head. We must then lift or depress the blade, and find, with the hand in the vagina, free space. This is why we insist on the hand being in the vagina. Especially is this important when the head is high up, for then the end of the fenestra must enter the uterine cavity, and, at times, scarcely the finger-tips can reach the cervix and guide the fenestra, which must penetrate deeper even than these fingers. Let us add, too, that the cervix itself often runs away from the fingers. Here, then, we must re double our care and gentleness. The fund us of the uterus must be de pressed as much as is possible by the hand of an assistant, which, at the same time, steadies the head at the superior strait. This assistant may often thus feel the blades through the abdominal wall, and be cognizant of the fact that they grasp the head exactly.
In one word, the blades should penetrate easily, and adapt themselves, as it were, and, in case of obstacle, they should be withdrawn and rein troduced in an inverse manner. In taking out the blades, they must fol low, of course, the direction opposite to that in which they were intro duced.
The the first blade has been applied, it should be held in place by an assistant, without the least traction, and the second, gen erally the right, is inserted in the classic manner, and the instrument is to be locked.
If the blades have been well placed, and the head well grasped in its bi-parietal diameter, nothing is easier, usually, than the locking. It suffices to seize both handles, and to bring them together, the pivot inside the mortise, in which it fits exactly, and the pivot need only be turned to firmly join the handles. (Fig. 84.) But this is not always the case, and the obstacles to locking may be three: 1. Locking cannot take place, because the right blade is below the left. The blades must be crossed.