A textbook of obstetrics . ertex presentation. ished expulsive power, increased resistance or decrease in re-sistance, as occurs in cases of very large pelves, relaxed pelvicfloors, small and yielding heads. Anomalies of Flexion.—If flexion is imperfect, the anteriorvault of the cranium (as in those rare cases of presentation ofthe large fontanel), the brow, or the chin first strikes the pelvicfloor, and is, therefore, directed forward, and the occiput is thusdirected backward. Insuperable Obstacles to Forward Rotation.—In some cases itflexion is only fairly good, and the occiput dors first st
A textbook of obstetrics . ertex presentation. ished expulsive power, increased resistance or decrease in re-sistance, as occurs in cases of very large pelves, relaxed pelvicfloors, small and yielding heads. Anomalies of Flexion.—If flexion is imperfect, the anteriorvault of the cranium (as in those rare cases of presentation ofthe large fontanel), the brow, or the chin first strikes the pelvicfloor, and is, therefore, directed forward, and the occiput is thusdirected backward. Insuperable Obstacles to Forward Rotation.—In some cases itflexion is only fairly good, and the occiput dors first strike the pel-vic floor, the occiput rotates backward, because the large diam-eter of the head (fronto-occipital, 1 1 34 em.—453 in.) is engaged,and rotation from one oblique diameter of the pelvis to the other i68 THE MECHANISM OF LABOR. oblique is impossible, on account of the very tight fit (A thehead in the pelvis. The occiput is also directed backward for the same reason, if the fetal head is oversized. The wedge. V WT*^J& M^ 1 ? \1 k \ \ k, ujijfm WL I W i3& I ifl Fig. 219. — Posterior position of a vertex presentation : backward rotation f the ccii>ut. of a prolapsed extremity may prevent forward rotation. Insome deformities of the pelvis, particularly in kyphotic, generally ABNORMALITIES IN MECHANISM. 369 contracted, and Naegeles pelves, the occiput rotates there is an abnormal projection of the lumbar and sacralvertebrae, interfering with rotation of the shoulder, the headmay not be able to rotate anteriorly. Rarely there may berotation of the head without a corresponding movement ofthe body, and the result is an exaggerated torsion of theneck. I have seen a child fatally injured in this most of the reported cases, however, the infant has escapedunharmed. The Mechanism of Labor when the Occiput Rotates into the Hollowof the Sacrum.— The occiput is propelled forward over the peri-neum by increased flexion until the face is finally born
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Keywords: ., bookcentury1800, bookdecade1890, bookidtex, booksubjectobstetrics
