COURSE OF NORMAL BIRTH 69 



the foetus may meet with obstacles, viz. : the cervix uteri and 

 where the vagina runs into the vestibule. The former does 

 not interfere, provided it is fully dilated. In primiparse it 

 often happens that the cervix uteri is not sufficiently opened, 

 and the foetus is detained slightly at that spot. We proved 

 previously that this is partly caused by the early rupturing of 

 the allantoic bladder within the cervix uteri. 



The vagina is slightly contracted where it runs into the 

 vestibule. Here also the moving foetus meets occasionally 

 with difficulties and detention. At this spot the passage of the 

 calf is extremely painful, on account of its great supply with 

 sensory nerves. Birth is often retarded at this place, especially 

 in primiparae. 



F(ETAL DIMENSIONS WHICH MUST CORRESPOND WITH PELVIC 

 DIMENSIONS TO PERMIT NORMAL BIRTH. 



The following dimensions of the foetus demand considera- 

 tion : 



1. The transverse diameter of the head, or the bitemporal 

 line, which is quite pronounced in the calf, must be smaller 

 than the greatest width of the pelvic inlet or passage. 



2. The vertical diameter of the head, as well as the diameter 

 of the carpus, must not be greater than the height of the pelvic 

 inlet. The vertical diameter of the pelvic passage and outlet 

 do not offer difficulties. The vertical diameter of the pelvic 

 canal is greater than the one of the inlet, on account of the 

 convexity of the os sacrum and concavity of the pelvic floor, 

 while the outlet is expansible in an upward direction by tha 

 mobility of the coccygeal vertebrae. 



3. The vertical diameter of the thorax (sterno-dorsal 

 diameter) is always greater in the matured calf than the height 

 of the inlet, while the bicostal diameter plus both shoulders is 

 smaller than the greatest pelvic width. Nevertheless, normal 

 birth may occur, as the ribs, by accommodating themselves to 

 the pelvic inlet, are pushed back. In this manner the vertical 

 thoracic diameter is lessened materially, without increasing the 

 bicostal diameter. As a result of the backward movement o£ 



