The simplest case for applying the forceps is, where the head has already descended nearly to the os externum, and has begun to press upon the perineum: it is for this that the straight forceps is chiefly intended; and as this is the instrument which is generally used, we shall describe its application first.
_Mode of applying the forceps._ Having ascertained that the rectum and bladder are empty, examined the position of the head, and warmed and greased the blades, we proceed to introduce the upper or lower blade first, according as its lock is directed forwards: this precaution is for the purpose of preventing the locks being turned away from each other when brought together after the introduction of the second blade. The trochanter major will guide us as to the precise position of the patient's pelvis, and is especially useful in pointing out the direction of the left oblique diameter, in which the forceps (on account of the first position of the head being in the right oblique diameter) should be most frequently applied: in this case, we pass the upper blade, as it were, beneath the trochanter, and the lower one in the opposite direction.[86]
Let us suppose that the head is in the first position, with its sagittal suture parallel with the right oblique diameter of the pelvis, and that in accordance with the above rule, the upper blade is to be introduced first. Having passed one or two fingers up to the head, we guide the blade along them, depressing the handle so as to make the extremity of the blade lie closely upon the head, neither allowing the point alone to impinge upon the head, nor _vice versâ_, to protrude against the vagina. The extremity of the blade, therefore, must be our guide for the direction in which we hold the handle: we must carefully insinuate this by a gentle vibratory motion between the head and passage which surrounds it: the convexity of the head will show the course which it has to take, nor is there any need of passing the finger farther; for when once the extremity of the blade is fairly engaged between the head and passage, it will almost guide itself, and needs little more than to be pushed on gently, the handle gradually rising according to the curve of the blade. The shank or handle should, therefore, be held lightly like a pen, by which means the operator will possess much more feeling with his instrument, than if he grasped it with his whole hand. As the blade advances, he should keep his eye on the general form of the pelvis, the curve of the loins, the situation of the trochanter and symphysis pubis, and thus gain a more accurate idea of the course which the instrument must take. This will, in great measure, depend upon the situation of the head: if it be quite down upon the perineum, the blade should be pointed towards the promontory of the sacrum, and the handle turned downwards and forwards; if it be still in the cavity of the pelvis, and only beginning to engage in the outlet, the blade must be directed upwards towards the centre of the brim, and the handle turned directly downwards. Having passed the blade to its full extent, we must press the handle backwards against the perineum, to allow sufficient room for the introduction of the second blade, and give it to an assistant or the nurse, with the caution to hold it steadily and firmly, especially during the pains, when it is apt to slip into the hollow of the sacrum if held carelessly.