The longitudinal presentations, however, constitute something over 99 per cent. of all cases and are regarded as normal, since the child occupying this relationship may be born spontaneously. In about 3 per cent. of the longitudinal presentation the breech is the presenting part and in about 97 per cent. it is the head. Of these, the vertex presentation is the one most commonly seen and is the one in which the child is most easily delivered. Face presentations are very rare, occurring in only a fraction of 1 per cent. of all cases. In addition to the child’s presentation, there is also its _position_, which is an entirely different matter, for in each longitudinal presentation the presenting part may occupy any one of six positions. By _position_ is meant the relation of some arbitrarily chosen point on the presenting part of the fetus, to the right or left side of the mother, and to the front (anterior), side (transverse) or back (posterior) segment of that side. Taking these up in turn, we find, that in transverse presentations the shoulder, _acromion_ process, is the point on the baby’s body which is chosen, to give the four possible positions their names. In breech presentations the sacrum is the arbitrarily chosen point. In face presentations it is the chin, or _mentum_, while in vertex presentations the occiput is the point chosen. Presentation, then, describes the relation of the long axis of the entire fetal body to the mother’s body, while position describes the relation between the baby’s shoulder, sacrum, face or occiput to the mother’s pelvis. If the child is so placed in the uterus that the head is the presenting part; the neck arched with chin on chest, and the occiput directed toward the mother’s left side, and more to the front than to the side, the presentation would be longitudinal, of the vertex variety, and the position would be a left-occipito-anterior. The arbitrarily chosen point on the child’s body (the occiput) would be directed toward the left, anterior segment of the mother’s pelvis. This is the situation most commonly seen and the description of this presentation and position are abbreviated, by taking the first letter of each word, into L. O. A. [Illustration: FIG. 54.—Diagram showing the six possible positions in a vertex presentation. ] If the occiput were turned directly toward the mother’s left side, neither to the front nor the back, we should have a left-occipito-transverse, L. O. T., and if it were directed toward the left posterior segment of the pelvis the position would be left-occipito-posterior, or L. O. P. As there are three corresponding positions on the right side, anterior, transverse and posterior, there are six possible positions for the child to occupy in the vertex, or occipital presentations, as follows: