This class includes by far the greatest number of misshapen pelves. Its characters are as follow: the ileo-pectineal eminence approximates unnaturally to the promontory on one side; that half of the pelvis has a diminished oblique diameter, it stands on a higher level, and inclines less than the other. The causes which lead to such a change of form are lateral curvature and torsion of the sacrum, and straightening and encroachment inward of so much of the linea arcuata as lies between the acetabulum and symphysis. It is a class which includes those frequent deviations from the natural form of the pelvis that arise from lateral curvature, and yet more frequent primary deformities induced by rickets, as well as those which result from dislocation of one hip, whether in consequence of violence or from previous disease of the joint. Of the last, which is the most common cause, I shall speak further presently.

The pelvis is sometimes oblique at the time of birth, but much more frequently it becomes so afterwards. There is much interest attaching to those congenital obliquities of the pelvis, which originate in faulty formation, as contradistinguished from those which are produced by disease in the foetus. One of these, in particular, has been described by Nägele, under the name of the obliquely contracted, or obliquely oval, pelvis.

The deformity so named, is founded in congenital anchylosis of one sacro-iliac synchondrosis, and in arrested growth of the lateral mass of the sacrum, and of the ilium on the same side.

The principal other characters of the obliquely contracted pelvis arise out of these two; and in two specimens in the pathological collection at Vienna (in both which the anomaly is on the right side), they are seen to correspond in all particulars with Nägele's lucid description: they are as follow:

The sacrum appears displaced towards the anchylosed side, and its anterior surface is turned more or less in the same direction; the symphysis pubis is driven towards the other side, and therefore lies obliquely, not directly, opposed to the promontory.

The lateral wall of the pelvis on the side adjoining the anchylosed part is flatter and straighter than natural.

On the other side, the line which separates the greater from the true pelvis, is less curved than usual in its posterior half, but more so anteriorly; this anomaly, together with its remote consequences, is often found also in obliquities that come on after birth.

Hence it follows, that the pelvis is obliquely contracted from the sound sacro-iliac joint to the opposite acetabulum, whilst the measurement between the anchylosed synchondrosis and the acetabulum, on the healthy side, is not only not diminished, but is greater than usual:

That there is less distance on the side of the anchylosis than on the sound side, between the promontory and the vicinity of the acetabulum, and between the point of the coccyx and the ischial spine:

That the posterior superior spine of the ilium is further removed from the lower border of the symphysis pubis on the anchylosed than on the articulated side:

That the walls of the pelvic cavity converge somewhat at their lowest part in an oblique direction, and that the arch of the pubes is more or less narrowed:

And that the aspect of the acetabulum on the flattened side of the pelvis inclines rather forwards, while on the other side it looks almost directly outwards.

In the specimens preserved in the Vienna Museum, the lumbar part of the vertebral column is distinctly curved towards the abnormal side of the pelvis.

There is another form of unsymmetrical pelvis, which is allied to the preceding, but subordinate to it in degree, and generally indeed is only just discernible. The deformity is found in persons in whom the last lumbar has on one side been converted into a sacral vertebra. The inequality in the pelvis consists in its greater capacity on the side of the anomaly in lumbar vertebra, the linea innominata of that side describing a larger and shallower curve, and being more inclined than its fellow. The opposite half of the pelvis is in the contrary state; and with that state is combined a slight curvature and rotation of the vertebrae towards the less capacious side, - an anomaly which is remarkable for the analogy it bears to the condition of the pelvis in lateral curvature, and which is constantly found in the lumbar region of the spine whenever its last vertebra is thus converted into a sacral. In cases in which this peculiarity in the last lumbar vertebra exists on both sides, the projection of the promontory is very slight, the conjugate diameter is great, and the inclination of the pelvis considerable.

Almost all the obliquities of the pelvis which come on after birth are of rickety origin. We have seen that when the sacrum, and consequently the pelvis, incline too much backward, and the latter is at the same time narrowed symmetrically, a compensatory curvature forward, a genuine lordosis, takes place in the lumbar region. In the same manner, when one side of the pelvis is contracted in consequence of a deviation of the sacrum from its mesial direction, the anterior curvature in the loins inclines somewhat laterally towards the contracted side. Thus the obliquities of the pelvis, in cases of rickets, are at once the starting-point and the occasion for lateral, or more commonly antero-lateral, curvatures in the loins; and these are succeeded by supplemental deviations of the dorsal part of the column towards the opposite side and backwards. Such is the state of the spine when the deviation is a compound one; and the conclusion to which an analysis of it leads is the same, so far as regards the deformity of the pelvis, as that which was elicited by an examination of the condition of the pelvis in primary lateral curvature: in both cases, the abnormal half of the pelvis is on the side opposite to the dorsal curve of the spine.