Not less incorrect is the theory (for we can call it nothing else) of the head presenting with the vertex, and turning with its long diameter, from the oblique, into the antero-posterior or conjugate diameter, and the face into the hollow of the sacrum, for it is disproved by all the above-mentioned facts, which careful examination during labour puts us in possession of. When the head is born, the face looks backwards and to the right, viz. to the back part of the mother's right thigh, for the shoulders are by this time passing through the pelvis in its left oblique diameter, the right shoulder being forwards and to the right, and lowest in the pelvis: it is also that which is first expelled. Such is the manner in which the head presents in the first or most common position: a slight modification of it is occasionally observed during the early stages of labour, without influencing the favourable character of its progress: the head at first is in the left oblique diameter of the pelvis, the occiput towards the left sacro-iliac synchondrosis, the anterior fontanelle towards the right acetabulum; but as the labour advances, the head turns, so that the occiput corresponds to the left acetabulum, the anterior fontanelle being turned towards the right sacro-iliac synchondrosis, the sagittal suture running parallel with the right oblique diameter of the pelvis. This peculiar commencement of the labour is probably not detected so frequently as it really occurs, owing to its changing into the common position at so early a period. _Second position of the cranium._ The other or second position of the cranium is, where the _left_ side of the head presents. It is, in fact, merely the reverse of the one just described: the sagittal suture crosses the os uteri at the beginning of labour, as in the former case, only now the posterior fontanelle is turned to the right instead of to the left; it is the _left_ parietal protuberance which is deepest in the pelvis, and which the finger first touches upon. As the labour advances, and the head approaches the pelvic outlet, it is the posterior and superior quarter of the _left_ parietal bone which first enters the vagina and protrudes through the os externum, and upon which the swelling of the scalp or _caput succedaneum_ is situated.