A manual of practical obstetrics . onsequence ofshoulders rotating upon inclined planes—left shoulder to RIGHT OCCIPITO-POSTERIOR POSITION 191 pubes, right to coccyx, the latter one generally escapes of the body. Thus we have described the two anterior positions of theocciput: L. 0. A. and R. O. A. Next come the two posteriorones. Mechanism of R. O. P. Position (Occiput to RightSacro-iliac Synchondrosis) ; 1. Flexion, and 2. Descent, as in anterior positions of theocciput. 3. Rotation.—In the large majority of cases (96 per cent.),the occiput rotates all the way round to the sym
A manual of practical obstetrics . onsequence ofshoulders rotating upon inclined planes—left shoulder to RIGHT OCCIPITO-POSTERIOR POSITION 191 pubes, right to coccyx, the latter one generally escapes of the body. Thus we have described the two anterior positions of theocciput: L. 0. A. and R. O. A. Next come the two posteriorones. Mechanism of R. O. P. Position (Occiput to RightSacro-iliac Synchondrosis) ; 1. Flexion, and 2. Descent, as in anterior positions of theocciput. 3. Rotation.—In the large majority of cases (96 per cent.),the occiput rotates all the way round to the symphysis doing so, it passes the right acetabulum, but it no soonerreaches this point than it becomes practically, and in reality,a right anterior position, and the rest of the mechanism isprecisely the same as already described for the R. O. A. posi-tion. In the small minority of cases (four per cent.), the occiput,instead of rotating forward, rotates backward to the sacrum,and the forehead comes to the pubes. Fig. Extension after posterior rotation. Then follows, 4. Extension, which takes place, not upwardtoward the mons veneris, but the occiput escapes over theperineum, and is depressed outside of it downward and back-ward toward the anus, while forehead, nose, mouth, and chinsuccessively emerge under the pubic arch. (See Fig. 56.) 192 LABOR IN HEAD PRESENTATIONS. 5. Restitution.—By internal rotation of the shoulders, asalready explained, one goes to pubes, the other to sacrum, andthe occiput rolls round to the right thigh (the thigh corre-sponding to the sacro-iliac synchondrosis at which it originallypresented). Mechanism of L. O. P. Position (Occiput to LeftSacro-iliac Synchondrosis) : 1. Flexion. 2. Descent. 3. Rotation, in the majority of casesall the way round to the symphysis pubis (when, on reachingleft acetabulum, it, of course, becomes converted into an A. position); in the minority of cases, backward rotationof occiput to sacrum. 4. Extensio
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