The blade and the curve are exactly similar to those of the ordinary for ceps, with the single exception that the fenestne are not quite as long. The distance from the end of the fenestrre to the lock is 10} inches; from the same point to the ends of the traction rods it is 9t inches. There is a space of I of an inch between the ends of the blades when the instru ment is locked. The greatest distance between the blades is 21 inches as in the classical forceps. The introduction and use is the same as the latter, except in the following respects: The compression screw; traction is made by rods, always at about I of an inch from the handles; as soon as the head is about to escape at the vulva both the handles and rods are seized near the blades, to prevent too rapid exit of the head. (Vide Fig. 79.) Thus modified, Tarnier's instrument is an excellent one, for to the classic rceps he has added, in our opinion, two improvements, in the pelvic (-ovation, certainly. The indicator needle, by showing the direction in :rich traction should be made, is of great utility, and less force has to employed in traction than with the classic forceps. The same is not tie at the superior strait, for the last model lacking the perineal curve, ere is the same difficulty with Tarnier's instrument as with the classic carrying it sufficiently backwards, and the force to be used is identical both instances.
The objections to the instrument are, in our opinion, still numerous: A two-fold manipulation is requisite, the one for articulation of the s even as in the classic forceps, the other for the insertion of the m rods. In order that these rods may functionate properly, they must absolutely parallel—that is to say, the head must be seized Hy, and this, while easy enough in the cavity or at the inferior strait, difficult, if not impossible, at or above the superior strait. Further, ten the head is high up, the lock is at the vulva, and the traction rods, lug shorter than the handles, must, necessarily, be adapted within the Iva. This objection, however, is not insurmountable, and may readily rectified. Tarnier's figures, as Pajot points out, represent the forceps plied to the head already engaged, and not above the superior strait, ;Mt is what Tarnier aims at. It is evident that the difficulty of ;ion is far greater above than at or within the superior strait. 2. The ;trument is, above all, intended to puffin the mathematical axis of the lvis, and yet, as Pajot points out, it is not possible to limit this axis, for it differs in each pelvis, and, according to Dubois and " there are gentlemen who have endeavored to be lly exact in their researches, and who, to attain their end, have invoked it aid of geometry for the settlement of scientific questions, when this I is not only useless, but really superfluous." Tarnier has not
etended to make traction with his instrument in the exact mathematical lvic axis, for he says, " it will doubtless be said that the expert eur knows how to give to the forceps a direction which gives to the head movement in exact accord with the pelvic curvature. In order that is may be true, while making traction the handle should follow a line actly like that represented by the letters f, m, n, f . (Fig. 80.) Even ough they have as a guide only uncertain anatomical rules, since the ape of the female pelvis is ever variable, a skilled artist would have trouble fn exactly reproducing this line. How then can an accoucheur be expected to follow it, especially when, at the same time, be must make the traction ?" The above objection, stated by Tarnier himself, applies perfectly to his forceps. How, says Pajot, can Tarnier make traction in an axis which is unknown to him ? 2. With Tarnier's forceps, before making traction, the precaution must be taken to turn the compression screw in order to fix the head. As stronger traction is made, the head is compressed by the walls of the canal through which it is passing, and the head, therefore, tends to become smaller, of necessity; then the screw must from time to time be tightened.
3. The greatest objection we have to Tarnier's instrument is the follow ing: With the classic forceps, the acconcheur is at all times conscious of the progress made by the foetal head; with Tarnier's, however, he is not at all. When the head resists, greater traction is made. If it descends, all the better, if it does not we pull harder still; thus nothing indicates the limit. Traction, therefore, may readily be exaggerated, and serious damage be done.
4. Although Tarnier s forceps is just as firm in hold as the classic, it is nevertheless the compression screw alone which retains the handles in appo sition. The head may be seized incompletely with this instrument, even as with the classic, and consequently it is just as likely to slip. This has happened to us twice, and to Budin once. Now with the classic forceps held in the hand, we know at once when it is slipping, and this may be prevented. Not so with Tarnier's forceps. The hand pulls on the trans verse bar of the traction rods, and is no longer conscious of slipping of the instrument from the head, which may result in vaginal and vulvar lesions, not to speak of uterine, the greater the stronger the exerted trac tion.
5. When Tarsier's forceps is applied at or above the superior strait, since the perineal curve is absent, the disadvantages are as great as in the classic forceps.