649 
of Edinburgh, Session 1871 - 72 . 
well known ; but they can be carried on to a great degree of ad- 
vancement, even while the amount of power exerted by the machine 
is unknown, or at least unsettled. 
Some of these inquiries as to the action of the force of labour 
upon the foetus and passage are very easily solved, and have been 
long in this condition. But the most, and by far the most, import- 
ant are questions only recently raised ; and of which it may be 
said that few are familiar to the profession even as questions, and 
still fewer can be regarded as settled. These inquiries form the 
natural sequel- to the most recent developments of our knowledge 
of natural parturition. These have been chiefly engaged in de- 
scribing how the foetus and the passages actually behave during 
the process, while the new inquiries are destined to explain why 
they so behave. These new inquiries will introduce us far more 
deeply into the subject of the mechanism of labour than those 
which have preceded them. They are specially difficult because 
of the varying conditions of the force of labour and of the corre- 
lated parts, the foetus and the passage. The former has the relations 
of its parts extensively changed while the process of labour pro- 
ceeds, and the latter is only produced at the time by what is called 
the development of parts, as the foetus advances. 
The subject to which I wish at present to direct attention is the 
curves of the genital passage, and their influence on the pheno- 
mena of parturition. 
I. The first curve to which I direct attention is said to be at the 
brim of the pelvis, and to have its convexity directed downwards 
and forwards. I do not admit that the curve exists, but it is of 
the utmost importance to decide the point, because, without doing 
so, we cannot possibly determine the primary direction of the driv- 
ing force of labour. Hitherto and now, the axis of the gravid 
uterus has been and is generally regarded as coincident with the 
axis of the brim of the pelvis, and to indicate the direction of the 
resultant of the forces of parturition. But an elaborate attempt has 
been recently made by Schatz and Schultze, especially by the former 
of these authors, to demonstrate that the axis of the uterus at rest 
and in action is inclined to the axis of the brim of the pelvis, at a 
small angle opening forwards and upwards, and of about ten 
degrees. I have just said that the axis of the uterus has been 
generally considered to indicate the primary direction of the driv- 
