Normal Parturition 523 



power upon the fetus essential to its ready expulsion. The 

 uterus maintains a more or less spherical shape while the fetal 

 fluids are retained, and consequently presses alike upon all por- 

 tions of the fetus, and tends to press it backward through the 

 vagina and vulva. 



When dystokia occurs and the fetal fluids all escape, the ob- 

 stetrist is made to realize the disadvantage of the absence of 

 these and the close investment of the fetus by the uterine walls. 

 This condition prevents him from readily changing the position 

 of the fetus or from carrying out other manipulations. After the 

 position of the fetus has been adjusted, the obstetrist still needs 

 the fetal fluids. The uterine and abdominal contractions tend to 

 force out some of these liquids with each labor pain, and conse- 

 quently keep the passage constantly moist and somewhat 

 unctuous throughout the entire duration of normal parturition. 



The dilation of the passages is favored by the part of the fetus 

 which normally presents. In the larger herbivora, the vast 

 majority of fetuses present with the two anterior feet, followed 

 shortly by the nose resting upon them at about the middle of the 

 metacarpus. The three extremities constitute an elongated 

 cone, which acts as a wedge in gradually dilating the passages. 

 If the fetus presents posteriorly, the conditions are essentially 

 the same, in reference to the mechanical plan, and the two hind 

 feet present together. As the legs and thighs are advanced they 

 serve again as a long wedge or cone to graduallj^ dilate the pas- 

 sages for the expulsion of the fetus. In carnivorous animals, 

 where the head is proportionately very large and the anterior 

 limbs are comparatively small and flexible, the head usually ad- 

 vances alone and the fetus is expelled with the anterior limbs 

 lying along the side or floor of the fetal chest. 



When the young of large herbivora present anteriorly there is 

 usually no very serious impediment to their progress until the 

 head of the fetus reaches the vulva, when, especially in primipara, 

 there is a delay in the progress of the fetus because time is re- 

 quired to bring about the dilation of the vulva to such a degree 

 that the fetus can pass through without serious injury to the 

 part. When the head emerges from the vulva, the other parts 

 of the fetus usually pass with less difiiculty, though there may 

 be marked resistance when the chest enters the passages and 



