A manual of obstetrics . e exact cause of the spinalextension is not known. (2) Now follows intanial anteriorrotation of the occiput from left to right, the brow at thesame time rotating posteriorly into the hollow of the sacrumfrom right to left. There has been, and still is, considerablecontroversy as to why the occiput rotates anteriorly in ver-tex presentations. The old view, that of Baudelocque andhis followers, was, that it was due to the presence of theischial spines, which converted the pelvic cavity into twoinclined planes, an anterior and 2i posterior, and according asto whether the
A manual of obstetrics . e exact cause of the spinalextension is not known. (2) Now follows intanial anteriorrotation of the occiput from left to right, the brow at thesame time rotating posteriorly into the hollow of the sacrumfrom right to left. There has been, and still is, considerablecontroversy as to why the occiput rotates anteriorly in ver-tex presentations. The old view, that of Baudelocque andhis followers, was, that it was due to the presence of theischial spines, which converted the pelvic cavity into twoinclined planes, an anterior and 2i posterior, and according asto whether the head entered the one or the other of theseplanes was its anterior or posterior rotation view, however, failed to account for the anterior rota-tion of posterior positions of the occiput. Tarnier claimedthat it was the outcome of the inclination of the pelvis, butthe researches of Paul Dubois, and later of J. Clifton Edgarof New York, have proved conclusively that anterior rota- I40 A MANUAL OF tion is accomplished mainly through the agency of thetissues of the pelvic floor. This great function of the peri-neum has been formulated into the following law: What-s ever portion of the fetal presentation first strikesthe pelvic floor, whetherit encounters this struc-ture behind or in frontof the median transverseline, will be directedforward under the sym-physis pubis. The peri-neum is so attached tothe bony structures ofthe pelvis that it forms a Fig. 59.—Diagram showing direction and amount plaUC directed obliouelyof rotation of occiput in L. O. A. position: S, sym- r 1 1 j physis pubis; 5, sacrum; £, left iliopectineal em- irom abOVC dOWnward ^- and from behind for- ward, witR the lowest point terminating directly under thesymphysis pubis at the vulvar orifice. As a result, theadvancing head, following the direction of least resistance,rotates toward the anterior median line. In cases of relaxedor torn perineum this dominating influence is lost, and
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectobstetrics, bookyear1
