294 NATURAL EUTOCIA. 



725. In this position the head of the child does not pass through 

 the pelvis without undergoing four particular motions. 1st, flexion; 

 2d, rotation; 3d, extension; 4th, restitution. 



Flexion. Immediately after the rupture of the membranes, the 

 uterine contractions must necessarily press the several parts of the 

 foetus upon each other; being pressed from above downwards, the 

 spine causes the head to bend forwards so that the occiput sinks 

 towards the centre of the pelvis, and the chin is squeezed more or 

 less firmly against the breast. This flexion movement does not 

 seem to have been well understood, even by the most esteemed 

 authors. They teach us that antecedently to the very first contrac- 

 tions of the womb, the head should be, disposed in such a manner, 

 that its occipito-frontal and bi-parietal diameters should be parallel 

 to the oblique diameters of the strait; whose axis would then be re- 

 presented by the vertical diameter of the fcetus. According to them, 

 the object of the flexion motion would be to alter all these relations; 

 that is to say, to compel the occipito-mental and occipito-bregmatic 

 diameters to assume the places of the vertical and occipito-frontal 

 diameters, which would be much more favorable. In order that the 

 above might be correct, it would be necessary for the chin, during 

 pregnancy, to be kept habitually remote from the breast, which it 

 would not approach until the period of labor, otherwise the occipito- 

 frontal diameter cannot be parallel to one of the diameters of the 

 pelvis; but, it is well known that the fostus, in the natural state, is 

 always doubled up, and that its chin is pressed upon the sternum. 

 The flexion motion therefore really takes place long before the 

 commencement of labor, and instead of being wholly eflfected, is 

 only a little increased during labor. 



726. In this way the occiput by being depressed, soon corresponds 

 to the centre of the superior strait; the occipito-bregmatic diameter 

 is then parallel to the oblique diameter, which extends from left to 

 right and from front to rear; the bi-parietal diameter represents the 

 other oblique diameter; the occipito-mental diameter is parallel to 

 the axis of the pelvic circle, and the occipito-bregmatic circumference 

 corresponds to the plane of the strait. 



727. Rotation. In this state the head is disposed in the best pos- 

 sible manner to pass without difficulty through the upper strait; by 

 successive pains it is forced to descend a little; it reaches the excava- 

 tion, and being soon stopped by the floor of that cavity, it executes 

 the rotation or pivot motion; that is to say, it turns upon its great 

 axis, the occiput sliding upon the left anterior inclined plane, from 

 behind forwards and from left to right, so as to place itself behind 

 the symphysis or under the arch of the pubis, while the forehead 



