II. DYSTOKIA OF THE POSTERIOR PRESENTATION. 



I. DOKSO-ILIAL AND DORSO-Pl'BIC POSITIONS. 



When considering the normal course of birth we had occasion 

 to observe that a fetus presenting posteriorly, especially in the 

 larger domestic animals, may pass quite readily through the 

 pelvic canal, so long as it is in the dorso-sacral position ; but, 

 whenever it deviates to any great extent from this, its passage 

 becomes more or less difficult or impossible, depending largely 

 upon the size of the fetus as related to the dimensions of the 

 channel through which it must pass. 



The dorso-pubic position is the most unfavorable, because, 

 owing to the curvature of the body of the fetus, the hind feet 

 project upward against the roof of the vagina, so that they may 

 readily become engaged in the vaginal walls and cause more or 

 less obstruction to the progress of the fetus, and at the same 

 time greatly imperil the integrity of the soft parts of the mother. 

 When the fetus is lying upon its back, its buttocks drop down 

 in front of the pubic brim in such a position that it is exceed- 

 ingly difficult for the contraction of the uterus and abdominal 

 walls to lift it up over the pubis and cause it to enter the pelvic 

 canal. 



The indications in these positions are to bring about an ad- 

 justment by rotating the fetus upon its long axis, as described 

 on page 632. 



Some obstetrists hold that the fetus ma)-- pass through the 

 canal somewhat easily when in the dorso-ilial or dorso-pubic po- 

 sition, and that, in either of these positions, it may often be 

 forcibly extracted without serious peril to the mother, but ac- 

 cording to general experience such positions offer more or less 

 serious obstacles to delivery, especially in the calf and the foal. 



If the fetus is very large, the amount of traction necessary to 

 bring it away passes the limit of safety ; if the amount of force 

 required is not great it is usually very easy to bring about rota- 

 tion and delivery by the more natural method. Thus, forced 

 extraction has a very limited application in this form of dystokia. 



Embryotomy might be demanded in very rare cases, where, 

 owing to firm impaction in the pelvic canal, rotation becomes 

 impossible and forced extraction unsafe. 

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