This may arise from there being either too much or too little resistance to the passage of the child; where, in the one case, labour is rendered difficult or impossible to be completed by the natural powers; in the other, it is unnaturally rapid. The latter condition belongs to the second great division of dystocia, where the faulty character of the labour does not depend upon its progress being deranged, but upon other circumstances: we shall, therefore, delay speaking of precipitate or too rapid labour from unusually large pelvis, until then, and devote the present chapter to the consideration of those cases where the labour is more or less obstructed by the faulty condition of the mother's pelvis. The pelvis may obstruct the passage of the child in a variety of ways. 1. It may be merely a diminutive or dwarfish pelvis, viz. well formed but smaller than usual in every direction--the pelvis simpliciter justo minor of Continental authors. 2. It may be distorted and deformed. 3. It may be of the natural form and size, but the passage through it more or less obstructed by exostosis. _Equally contracted pelvis._ The first species of faulty pelvis (_pelvis simpliciter justo minor_,) is not of common occurrence, and has received but little notice in this country. It has been said to resemble the pelvis of a girl in its general appearance; but this only holds good in point of size; for, in the relative proportions of its diameter, it presents all the characters of a well formed adult pelvis. From this circumstance, it can scarcely be said to be an arrest of development, the necessary changes in the form of the pelvis having taken place at the time of puberty, as completely as if it had been of the ordinary size. A pelvis of this sort may be not more than a quarter of an inch too small in every direction, or it may be as much as a whole inch: we do not know of any case where the diminution has exceeded this last degree.