The only part to which the forceps are intended to be applied is the head, to the dimensions and form of which they are specially adapted. Some practitioners have used them on the breech, but the practice is not generally sanctioned, because they seldom retain their hold on this part and are nearly sure to seriously injure the child when so applied. With properly constructed forceps, rightly applied to the head, there is but little danger either to the mother or the child; but in the hands of an unskillful or careless person the consequences of their use may be deplorable to both. It is scarcely necessary to remark that the forceps are neither _cutting_ nor _crushing_ instruments, but are simply intended to _lay hold_, like the hand itself, and enable us to draw down the head, or change its position. Most usually they are made long and curved, as shown in the above plate, but sometimes they are made much shorter and straight. They may be used upon the head when it is either at the upper or the lower straits, or while it is in the passage; but on no account should they be applied till the parts are fully dilated, and everything indicates that the child _can_ pass. Thus they should never be used when the head is too large, or the pelvis too small, nor when there are tumors in the way. In short no attempt should be made with them to _force_ the fœtus through a passage which will not admit it by reasonable efforts. M. Dubois says they should never be used when the pelvic diameter is less than _three inches_, because with such dimensions the child is nearly certain to be crushed to death, and the mother can scarcely escape serious bruises and lacerations. In like manner, if they are thrust into the womb before the mouth of it is naturally dilated they are sure to tear and injure it. It is not necessary here to give directions for using the forceps in every variety of presentation and position, but simply to show the mode of applying them as they are most frequently required. The two blades are adjusted separately, one to each side of the head, and then locked together, so that the head is firmly inclosed between them, but not crushed. Dr. Denman gives perhaps the best and simplest directions on this point, and I therefore quote from his work.