The principles and practice of obstetrics . ispatient, provided he have experience and tact sufficient to recog-nise the evolutions of the foetal head in its progress through thepelvic canal. Again : if we deny the action of the inclined planes,how is rotation to he explained in certain cases in which, fromnumerous antecedent deliveries, or other circumstances, such, forexample, as previous laceration of the perineum, there is such anamount of relaxation in the parts, as to render any attempt at resist-ance utterly negative? Extension.—When the head has been rotated, the relation of itsdiamete
The principles and practice of obstetrics . ispatient, provided he have experience and tact sufficient to recog-nise the evolutions of the foetal head in its progress through thepelvic canal. Again : if we deny the action of the inclined planes,how is rotation to he explained in certain cases in which, fromnumerous antecedent deliveries, or other circumstances, such, forexample, as previous laceration of the perineum, there is such anamount of relaxation in the parts, as to render any attempt at resist-ance utterly negative? Extension.—When the head has been rotated, the relation of itsdiameters to those of the lower strait is as follows: the bi-parietalor transverse diameter of the head, measuring three inches anda half, corresponds with the transverse or bis-ischiatic of the strait,which is four inches; while the occipitofrontal diameter of thehead, four inches and a quarter, rests in the direct or cocci-pubicdiameter of the strait, which, under ordinary circumstances, is four 4 50 THE PRINCIPLES AND PRACTICE OF inches, but, at the time of labor, owing to the regression of the coccyx, increases fromiour and :i half to fiveinches. It is not difficultto understand how thehead is made to its peculiar positionat the lower strait, afterrotation is effected, theposterior surface of thechilds neck is thrownclosely against the sym-physis pubis, which be-comes a point of resist-ance, so that the force ofuterine effort, which untilthis time had fallen onthe occiput, is now con-centrated on the chin; theresult of this change inFl0 26 the direction of the im- pelling power of the organis necessarily to cause the chin gradually to leave the sternum () until the movement of extension is completed. In confirmation of the fact that extension does really take place,watch carefully the first case of labor you may attend, with anoccipitoanterior position of the vertex, and you will find the fol-lowing to be the progress of the head as it emerges from
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Keywords: ., bookcentury1800, bookdecade1860, bookpubli, booksubjectobstetrics
