A system of obstetrics . Foetal Ellipse (vertex presentation, first position—from Hodge). At the superior strait, and before the bag of waters ruptures, thehead (in a first position of vertex presentation) offers only partiallyflexed, presenting really the occipito-frontal circumference, with its 570 MECHANISM AND TREATMENT OF LABOR. longer diameter, instead of the eervico-bregmatic circumference. When,however, the bag of waters ruptures and a portion of the liquor amniiescapes, the walls of the uterus come in direct contact with the bodyof the child and force it down into the pelvic cavity. T
A system of obstetrics . Foetal Ellipse (vertex presentation, first position—from Hodge). At the superior strait, and before the bag of waters ruptures, thehead (in a first position of vertex presentation) offers only partiallyflexed, presenting really the occipito-frontal circumference, with its 570 MECHANISM AND TREATMENT OF LABOR. longer diameter, instead of the eervico-bregmatic circumference. When,however, the bag of waters ruptures and a portion of the liquor amniiescapes, the walls of the uterus come in direct contact with the bodyof the child and force it down into the pelvic cavity. The head, meet-ing with resistance, becomes perfectly flexed. This flexion of the headunder these circumstances is readily understood when we bear in mindthe position of the foramen magnum at the base of the skull—that itis behind the centre; hence that portion of the head anterior to the. First Position of Vertex at Superior Strait. spinal articulation represents the long arm of the lever, and when anequal force of resistance is applied to the anterior and posterior por-tions of the head, flexion must result; and this flexion becomes per-fected as the resistance increases, until a complete vertex presentationis secured, and the eervico-bregmatic circumference fairly offers to thediameters of the superior strait or cavity of the pelvis. Hence thefirst effect of uterine contractions after dilatation of the os is to com-plete the flexion of the head, and thus the first effect of uterine con-traction is to perfect the foetal ellipse. We may call the flexion, thus secured, adaptation, since it causes thefoetal ellipse to offer its most favorable diameters to those of the we come to study the mechanism in other presentations we shallsee an attempt to secure similar results in every instance. In otherwords, Natures first effort seems to be to attempt to bring the
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectobstetrics, bookyear1
