653 
of Edinburgh) Session 1871 -72. 
ous pelvis. For, if we suppose with Schatz that the whole power 
of labour acts in an oblique line nearly corresponding to that of 
the axis of the uterus, or inclined still more posteriorly, then there 
will always be a tendency of the anterior half of the head, or of 
that which is nearer the concavity of the curvature of the passage, 
to descend first, and so produce the Naegele obliquity, if there be 
uniform resistance to the advance of all parts of the head. But, as 
the occurrence of Nsegele’s obliquity is now very generally denied, 
any mechanism which accounts for it derives little or no support 
of its own accuracy from the circumstance of its doing so. 
Still another difficulty in the way of admitting the presence of 
the curve of the natural promontory as the natural or ordinary con- 
dition is worthy of consideration. It is justly held that in natural 
labour the advance of the head through the brim of the pelvis is 
impeded only by friction and imperfect dilatation or dilatability of 
the soft parts ; but, if this curve of the natural promontory exists, 
a new and considerable difficulty is introduced, namely, the differ- 
ence between driving a body through a curved and a straight 
passage — a new difficulty which it appears to me unreasonable to 
admit. And this is not all ; for this addition of difficulty is not 
overcome and passed when the child’s head has traversed the curve, 
but lasts during most of the process of the birth of the child. If 
this curve exists, the axis of the genital passage, regarded in the 
antero-posterior vertical plane, has the shape of a Roman S ; its first 
or upper curve, the curve of the natural promontory, having its 
concavity looking backwards; its second and universally recognised 
curve having its concavity looking forwards. I believe we are 
nearer the truth when adopting the view at present generally en- 
tertained, that, in the antero-posterior vertical plane, the genital 
passage has ordinarily only one curve, having the concavity of its 
axis looking forwards. 
Direct therapeutical bearings of this matter are evident and 
important both in natural and morbid parturition. Certain atti- 
tudes of the body, by increasing or diminishing the flexion of the 
iliac beams upon the sacrum, a movement which I have elsewhere 
described as nutation of the sacrum,* may alter not only the dimen- 
sions of certain parts, but also the relations of the axis of the 
* Researches in Obstetrics, p. 148. 
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