The chief peculiarity is, that the change, which we noticed in the first position as an occasional occurrence at the beginning of labour, is in this case the regular commencement of it. In the second cranial position, the head at the beginning of labour, with very few exceptions, is always with its long diameter parallel with the right oblique diameter of the pelvis, the posterior fontanelle turned towards the right sacro-iliac synchondrosis, the anterior one towards the left foramen ovale. During the early periods of labour, when the head is passing through the brim, both fontanelles may be reached; and, generally speaking, the posterior one with greater ease, from its being usually somewhat the lower; but as labour advances, and the head has fairly engaged in the pelvic cavity, they may both be reached with equal ease, the anterior fontanelle still corresponding to the left foramen ovale, or rather to the descending ramus of the left pubic bone. "As soon as the head experiences the resistance which the inferior part of the pelvic cavity opposes to it, or, in other words, the oblique surface which is formed by the lower end of the sacrum, the os coccygis, the ischiadic ligaments, &c. by which it is compelled to move from its position backwards in a direction forward, it turns by degrees with its greater diameter into the left oblique diameter of the pelvic cavity, viz. the posterior fontanelle is directed to the right foramen ovale, and as the head approaches nearer and nearer to the inferior aperture, it is the posterior and superior quarter of the left parietal bone which is felt in the cavity of the pelvis opposite to the pubic arch, so that when the point of the finger is introduced under and almost perpendicular to the symphysis pubis, it touches nearly the middle of the posterior and superior quarter of the left parietal bone: and this is precisely the part, as the head advances farther, which first distends the labia, with which the head first enters the external passages, and the spot upon which the swelling of the integuments forms itself." (Naegelé, _Mechanism of Parturition_, transl.)