We have already stated that an intimate acquaintance with the mechanism of parturition is of the greatest importance in applying the forceps. Knowing that the head always presents in one of the two oblique diameters of the pelvis, and that the blades are applied on each side of the head, it follows that the forceps must always be applied in the contrary oblique diameter of the pelvis to that in which the head is. Before speaking of the operation itself, we must first consider what position of the patient will be the most convenient. In this country no alteration is made in her position, beyond bringing her close to the side of the bed, with the nates projecting as much as possible over the edge, for the greater convenience of the operator; unless this be attended to, it will be difficult to depress the handle of the upper blade sufficiently when introducing it. Upon the continent, and also in America, where the long forceps is more generally used, the patient is usually delivered on her back; she is placed in a half-sitting posture upon the edge of the bed, her back supported by pillows, &c., her feet resting on two chairs, between which the operator stands or sits, and applies the forceps in this position. This, in many respects, is the most convenient posture for him, but the very preparation which it requires cannot but be alarming to the patient, who is obliged to be a witness of all his manipulations; whereas, when she lies upon her left side, she is aware of little or no preparation being made, and if any slight exposure happens to be necessary, viz. at the moment of locking, it can be done without her knowledge.[85] 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]