Amongst the former are included specimens in which the pelvis is unnaturally large or wide in all its diameters, as well as those in which it is unnaturally small or narrow in the same respect. As pelves, which are unusually large or small in any one diameter, are generally in an opposite condition in some other dimensions, they will be treated of under the head of deformities. And small pelves, more especially, not only bear traces of their growth having been arrested in consequence of rickets, but they are, at the same time, also misshapen. We shall meet with various instances of such pelves amongst the following deformities. The essential characters of a rickety pelvis are, that it is small, i. e. low and contracted, especially in the conjugate and oblique diameters of the inlet; its capacity is small, its inclination considerable, and the arch of the pubes is widened. When this fundamental anomaly is extremely developed, or unequally on the two sides, it will be specially noticed as of rickety origin when it occurs in the following description.

As the importance of the subject of deformity of the pelvis arises chiefly from its connection with the mechanism of parturition, the principal interest is centred in the upper aperture or inlet. The great number of facts relating to the subject can best be arranged according to Osiander's division of deformed pelves; but, as that division does not include every deformity, it must be somewhat enlarged, by the addition of several subinordinate varieties, and by the interpolation here and there of an intermediate form.

Osiander enumerates six forms.

1. That in which the pelvis is elliptical in its transverse diameter; the ilia are widely separated from one another, and, as on the one hand, the promontory of the sacrum encroaches a little forward, and, on the other, the pubic bones are flattened, the conjugate diameter is less than natural, and the transverse measurement increased.

2. The kidney-shaped pelvis, in which the great projection of the upper part of the sacrum produces a deformity of that figure at the inlet.

There is a form of pelvis intermediate between these two, in which the base of the sacrum runs straight across the back of the inlet, and the linea arcuata bends forward from it at an angle.

3. That pelvis, the upper aperture of which may be compared to a figure of go. The extreme projection of the promontory on the one side, and the sinking backward of the symphysis and horizontal rami of the pubes on the other, produce a deformity in which the upper aperture appears divided into two lateral spaces, which are united by an intervening isthmus.

These deformities of the pelvis, with scarcely an exception, are always occasioned by rickets.

4. The pelvis, which is oval or elliptical in its conjugate diameter, the anteroposterior measurement exceeding the transverse. I have met with a deformity of this kind combined with angular projection of the spine.