A textbook of obstetrics . hen follows the delivery of the head by flexion and propul-sion, the mouth, nose, eyes, and forehead sweeping over the peri-neum and appearing successively at the posterior commissure. Restitution and external rotation follow the escape of thehead from the same causes that impose these movements uponthe head in a vertex presentation. The delivery ot the bodytakes place as in a vertex presentation. Abnormalities in Mechanism.—The most common and mostimportant anomaly of mechanism is a delay in the forwardrotation of the chin under the symphysis. This delay isdm- to th
A textbook of obstetrics . hen follows the delivery of the head by flexion and propul-sion, the mouth, nose, eyes, and forehead sweeping over the peri-neum and appearing successively at the posterior commissure. Restitution and external rotation follow the escape of thehead from the same causes that impose these movements uponthe head in a vertex presentation. The delivery ot the bodytakes place as in a vertex presentation. Abnormalities in Mechanism.—The most common and mostimportant anomaly of mechanism is a delay in the forwardrotation of the chin under the symphysis. This delay isdm- to the difference between the lateral depth of the pelvis( cm., or )*/& in.) and the length of the fetal neck ( cm., or1 J . in.), as a consequence of which tin- chin may not encounterthe necessary resistance t turn it forward, and without this for-ward movement it impossible tor the head to escape throughthe vulvar orifice. Should the chin bo directed posteriori)-, where t£NORMALITIES IN MECHANISM. 373. Fig. 222.—Face presentation, chin directed laterally.
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Keywords: ., bookcentury1800, bookdecade1890, bookidtex, booksubjectobstetrics
