A treatise on the science and practice of midwifery . Passage of the Shoulders and Partial Rotation of the Thorax. the child is now expelled, and as the head has entered the vagina, theuterus, having a comparatively small mass to contract upon, must obvi-ously act at a mechanical disadvantage. Still, the pressure of the headon the vagina is a powerful inciter, the accessory muscles of parturitionare brought into strong action, and there may be sufficient force to ensureexpulsion of the head without artificial aid. On account of the greatresistance to the descent of the occiput from its articul
A treatise on the science and practice of midwifery . Passage of the Shoulders and Partial Rotation of the Thorax. the child is now expelled, and as the head has entered the vagina, theuterus, having a comparatively small mass to contract upon, must obvi-ously act at a mechanical disadvantage. Still, the pressure of the headon the vagina is a powerful inciter, the accessory muscles of parturitionare brought into strong action, and there may be sufficient force to ensureexpulsion of the head without artificial aid. On account of the greatresistance to the descent of the occiput from its articulation with thespinal column, the pains have the effect of forcing down the anteriorportion of the head, and this ensures the complete flexion of the chinupon the sternum (Fig. 111). This is a great advantage from a mechan-ical point of view, as it causes the short occipito-mental diameter of the Fig. Descent of the Head. head to enter the pelvis in the axis of the uterus and the brim. If thehead should be in a state of partial extension, as sometimes happenswhen the pelvis is unusually roomy, the occipitofrontal diameter is PELVIC PRESENTATIONS. 305 placed in a similar relation to the brim—a position certainly less favor-able to the easy birth of the head. As the head descends it experiencesa movement of rotation, the occiput passing forward and to the right,behind the pubic arch, the face turning backward into the hollow of thesacrum. The body of the child will be observed to follow this move-ment, so that its back is turned toward the mothers abdomen, its ante-rior surface to the perineum. The nape of the neck now becomes firmlyfixed under the arch of the pubes; the pains act chiefly on the anteriorportion of the head, and cause it to sweep over the perineum, thechin being: first born, then the mouth and forehead, and lastly theocciput. Sacro-posterior Positions.—It is needl
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectobstetrics, bookyear1
