258 CAUSES OF LABOR. 



654. By carefully noticing the proceedings of nature, it will be 

 perceived that the idea of Haller expresses very well the mode in 

 which the diaphragm and abdominal muscles operate; but it is in- 

 correct, inasmuch as it attributes to tlie uterus only a secondary 

 part, whereas it is a matter of demonstration that its contractions 

 constitute the chief cause of delivery. Upon this hypothesis, the 

 expulsion of the ovum is almost wholly submitted to the volition of the 

 woman, but no one is ignorant of the fact that parturition is almost 

 entirely involuntary. Further, it was not so much Haller himself, 

 as his commentators, who desired to limit in this way the importance 

 of the uterine contractions; for that great man says positively, that 

 the efforts of the woman are not always indispensable to the termi- 

 nation of the labor. 



655. On the contrary, far from acting with so much power on the 

 womb, the diaphragm, as has been remarked by M. Bourdon, only 

 serves as a firm point cVappid for the abdominal muscles. When- 

 ever an effort is made, the chest dilates, the lungs fill with air, after 

 which the glottis closes; the diaphragm gives to the base of the tho- 

 rax, which is moreover supported within by the distended lungs, a 

 degree of immovableness and solidity, which affords to the muscular 

 powers a fixed point that they could not otherwise have obtained; 

 whence it follows, that it is not by pressing the viscera from above 

 downwards, as is generally supposed, that the diaphragm assists the 

 uterus, but rather by giving to the chest the power of resisting the 

 contractions of the abdominal muscles, which contractions are thus 

 rendered effective upon the body to be expelled. 



656. Tn most women the uterus is the first and only part to con- 

 tract until the foetus has reached the excavation of the pelvis. From 

 this moment a sense of weight, of straining, or of tenesmus, irre- 

 sistil^ly invites the concurrence of the contractions of the abdominal 

 muscles. Whilst the sole object of the womb is to dilate its neck, it 

 needs no aid; but when the orifice is sufficiently large, the foetus 

 must next be forced through a firm and very narrow canal, greater 

 powers become indispensable, and the uterus, redoubling its efforts, 

 rarely fails to solicit the action of all the muscles of the body. The 

 head and limbs being first fixed, the chest dilated, the diaphragm 

 depressed, the lungs filled with air, and the glottis closed, permits 

 the abdominal parietes, firmly attached to the pelvis and base of the 

 thorax, to contract from before backwards, as well as laterally; the 

 viscera, being unable to raise the phrenic septum which separates 

 them from the lungs, transmit directly to the fundus of the womb the 

 lively impression they have received; the latter organ, also sustained 



