PRESENTATION OF THE PELVIS. . 323 



left side, ?oon lakes place, and the bis-acromial again crosses the 

 occipito-bregmatic diameter at right angles. 



780. When fairly in the excavation, the head revolves on its 

 occipito-mental diameter, so as to carry the face directly backwards, 

 and the nape of the neck and occiput directly in front; the two ex- 

 tremes of the occipito-bregmatic diameter slide from right to left, 

 and from before backwards, on the right posterior inclined plane, 

 and from left to right and from behind forwards, on the left anterior 

 inclined plane, as in the first vertex position, so as to become parallel 

 to the coccy-pubal diameter. The womb can now no longer act 

 immediately upon the head, which is entirely or partly in the vagina 

 but the disposition to straining, produced by the pressure now ex- 

 perienced by the rectum and bladder, soon compels the woman to 

 gather up all her powers and redouble her courage, and the contrac- 

 tions of the abdominal muscles soon come to the assistance of the 

 powerless womb for whose forces they are now the substitutes. 

 From this moment the occiput receives the whole weight of the ex- 

 pulsive power: in order that it may become parallel to the axis of 

 the perineal strait, the occipito-mental diameter gradually executes 

 a see-saw motion, which brings the anterior fontanel near to the 

 anterior surface of the hollow of the sacrum, and causes the chin to 

 thrust the breast towards the symphysis of the pubis. Finally, the 

 nape of the neck, bearing upon the summit of the arch, as upon a 

 fixed axis, permits the head to describe an arc of a circle, the radii 

 of which seem to have the lower edge of the articulation for their 

 centre, and to be composed of the occipito-mental, occipito-frontal 

 occipito-bregmatic, and vertical diameters; so that we see the chin, 

 the forehead, and the anterior fontanel appear in regular succession 

 at the vulva, after which the occiput escapes from above downwards, 

 and emerges thus from the pelvis to put an end to the labor. 



B. Second Variety. 

 Loins forward and to the right. 



2d position of Baudelocque, Gardien, Capuron, Maygrier, Desormeaux and 

 Dugd?; 8() limes in 234 feet presentations, Madame Boivin; 175 in 37, 899 la- 

 bors, Madumc Lachapelle. 



781. In the right calcaneo-acetabular position, the soles of the 

 feet, the fore parts of the legs, and the whole anterior surface of the 

 foetus look towards the left and back part of the mother; the right 

 side is towards the front and left of the mother. 



The feet and legs as in the preceding position, are not mechani- 

 cally stretched out, are not really pushed into the orifice, until after 



