657 
of Edinburgh, Session 1871 - 72 . 
long axis of the uterus multiplied into the positive or negative 
difference of resistance by the walls of the pelvis, is greater on 
the posterior side of the foetus than the product of the same factors 
on the breast side. In the opposite circumstances face presenta- 
tion is produced.”* To all this ingenious theorising there can be 
no objection if the conditions are assumed. But the two chief 
premises are merely assumed ; they are not shown to occur ; they 
are not shown to be more likely to occur in face presentation cases 
than in others. Under these circumstances, I submit that there 
can be no hesitation in preferring the formerly described theory of 
face cases, where the corresponding assumptions or premises are not 
mere assumptions, but well-known facts ; I refer to the occasional 
lateral deviation of the uterus, the occasional dolichocephalous 
condition of the head, and the greater liability of cases of the 
second or right occipital position to be transformed into face cases 
than of the first or left occipital position. 
III. The last curve of the developed genital passage which falls 
to be considered is the most extensive and the best known. It is 
the great curve in the antero-posterior vertical plane, which begins 
about the middle of the third bone of the sacrum and extends 
through the outlet of the ligamentous pelvis to the outlet from the 
soft parts. Its length may be greatly diminished by rupture of 
the perineum, and still more if the sphincter ani is torn through. 
It forms a curve, whose amount of bending varies from about 60 to 
about 150 degrees. 
In connection with this curve fall to be studied the synclitic and 
allied movements of the foetal head during its progress, to which 
Kueneke has recently directed attention, and which have been so 
carefully discussed at home and abroad, f that it is unnecessary to 
re-enter upon them here. 
In connection with this curve have also to be studied the develop- 
ment of the lower part of the genital passage, the greater 
development posteriorly where the force is particularly or more 
strongly applied, than anteriorly where there is little more than 
* Der Geburt’s Mechanismus der Kopfendlagen, S. 72. 
t See Edinburgh Medical Journal, June 1870, and the American Journal 
of the Medical Sciences, October 1870, &c. 
