A system of obstetrics . tions I shall not refer to any part as theright or left part, as these designations are always confusing, but asthe anterior or posterior part; thus, the anterior or pubic shoulder, theposterior or sacral hip, etc., etc. Before entering on the description of the changes occurring in themechanism of the first position of the vertex, it may not be out of placeto remark that when the student understands thoroughly the mechan-ism of labor in vertex presentations he can readily comprehend, with-out the slightest difficulty, the mechanism of labor in all presentationsand pos
A system of obstetrics . tions I shall not refer to any part as theright or left part, as these designations are always confusing, but asthe anterior or posterior part; thus, the anterior or pubic shoulder, theposterior or sacral hip, etc., etc. Before entering on the description of the changes occurring in themechanism of the first position of the vertex, it may not be out of placeto remark that when the student understands thoroughly the mechan-ism of labor in vertex presentations he can readily comprehend, with-out the slightest difficulty, the mechanism of labor in all presentationsand positions. Perhaps I can give a clearer idea of my meaning bycomparing the mechanism of labor in vertex presentations to a tune, ofwhich tune the mechanism of labor in all other presentations is thesame, with variations. If the student shall get the harmonies of thissimple (and beautiful ?) tune fixed in his memory, he will have littledifficulty in adapting the self-evident variations to any presentation offering. Fig. 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
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectobstetrics, bookyear1
