MECHANISM OF DELIVERY IN PRESENTATIONS OF THE FACE. Presentations of the face appear to result from the head being bent backwards, instead of forwards upon the chest. They are easily recognized, because the face has so many peculiar parts, as the nose and mouth, for instance, which are altogether unlike what can be felt in any other presentation. In a very early stage the forehead may be taken for the vortex, unless care be used, because it _feels_ round and soft like it, but the mistake cannot last long. The positions in this presentation, as formerly explained, are determined by the chin, and in practice only two are noticed--the _right posterior mento iliac_, and the _left anterior mento iliac_. In the first the chin is on the right side, near the sacrum, and in the second it is on the left side, near the pubes. These answer, it will be seen, to the two principal positions of the head itself. It is generally considered that, though the chin, like the head, may assume other positions, yet it does so in but very few cases, and these presenting no peculiarities which require special notice. DELIVERY IN THE RIGHT POSTERIOR MENTO ILIAC POSITION OF THE FACE. The head descends with the forehead and chin nearly on a level, and the nose occupying the middle of the passage. When fairly in the cavity it rotates, the chin being brought under the pubes, while the back of the head passes into the curve of the sacrum. This is nearly always the process; no matter where the chin may be when the labor commences, it seldom fails to move under the pubes before it concludes. Occasionally it may rotate the other way, and pass into the hollow of the sacrum, while the occiput comes in front, but this is very rare. The chin is born first, and then follows, below, the forehead, top of the head, and finally the occiput--the face turning upwards towards the mother's abdomen, as each part is successively delivered. When the head is fully born, the body rotates inside the same as in the head presentation, and the delivery concludes in precisely the same way. [Illustration: PLATE XXXIV. Fig. 1.--The chin just passed, in presentation of the face. Fig. 2.--The head full born in presentation of the face.--_p._ The Pubic bone.--_c._ The Coccygis.] DELIVERY IN OTHER POSITIONS OF THE FACE. The delivery is precisely the same in all the other positions of the face, excepting that in some of them the chin has further to rotate before it can pass under the pubes. In all cases however, it may be safely calculated that it will do so, there having been so few instances known in which it has rotated the other way, into the hollow of the sacrum, which is fortunate, for there is always more or less difficulty and danger when it does so. Sometimes the rotation does not take place at all, but the face descends diagonally, as the head occasionally does.