A treatise on the science and practice of midwifery . Passage of the Shoulders and Partial Rotation of the Thorax. of the child is now expelled, and as the head has entered the vagina,the uterus, having a comparatively small mass to contract upon,must obviously act at a mechanical disadvantage. Still the pressureof the head on the vagina is a powerful inciter, the accessory muscles 292 LABOR. of parturition are brought into strong action, and there is usuallyquite sufficient force to insure expulsion of the head without artificialaid. On account of the great resistance to the descent of the oc
A treatise on the science and practice of midwifery . Passage of the Shoulders and Partial Rotation of the Thorax. of the child is now expelled, and as the head has entered the vagina,the uterus, having a comparatively small mass to contract upon,must obviously act at a mechanical disadvantage. Still the pressureof the head on the vagina is a powerful inciter, the accessory muscles 292 LABOR. of parturition are brought into strong action, and there is usuallyquite sufficient force to insure expulsion of the head without artificialaid. On account of the great resistance to the descent of the occiputfrom its articulation with the spinal column, the pains have the Fig. Desceut of the Head. effect of forcing down the anterior portion of the head, and thisinsures the complete flexion of the chin upon the sternum. This isa great advantage from a mechanical point of view, as it causes theshort occipito mental diameter of the head to enter the pelvis in theaxis of the uterus and the brim. If the head should be in a stateof partial extension—as sometimes happens when the pelvis is un-usually roomy—the occipital frontal diameter is placed in a similarrelation to the brim, a position certainly less favorable to the easybirth of the head. As the head descends it experiences a movementof rotation, the occiput passing forwards and to the right, behind thepubic arch, the face turning backwards into the hollow of the body of the child will be observed to follow this movement, sothat its back is turned towards the mothers abdomen, its anteriorsurface to the perineum. The nape of the neck now becomes firmlyfixed under the arch of the pubis, the pain
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Keywords: ., bookcentury1800, bookdecade1870, bookidtre, booksubjectobstetrics
