:Interior Vertex Presentation.—This presentation produces the least dis tortion. The head is more rounded. The transverse flattening and diag onal displacement of Dohrn occur.
Budin, measuring the diameters immediately after labor, and then forty eight hours after labor, i.e., when the head has resumed its original form, deduces from his measurements that: 1. The diameter 0. M. is always increased, sometimes even to 2.48 inches.
2. The diameter sub-O. M., the maximum diameter, is always lessened .28 inches.
3. The diameter 0.F. is almost always elongated.
4. The diameter 8.0.B. is always most lengthened, inch.
5. The diameter B. P. increases, but less than any other.
6. The diameter B. T. increases more than B. P.
These measurements are those made forty-eight hours after labor.
Budin concludes, from them, that: " In normal vertex labors, the di ameters O. M. and O.F. diminish instead of increasing, as is generally supposed. The antero-posterior diameter, which increases, is a sub-occi pito-mental or maximum diameter, hitherto always confounded with the diameter 0.M. The diameter S.O.B. is sometimes considerably lessened." The diameter B.T. also diminishes during expulsion. The diameter B.T., instead of being most diminished, is least so. This passive mechan ism, affecting the head of the foetus, is explained: A. By the existence of the fontanelles. B. By the situation of the different sutures. C. By the arrangement and structure of the bones of the cranial vault, particularly: 1. By the existence of a fibro-cartilaginous hinge which, at birth, unites the basilar process to the occipital bone; 2. By the suppleness, and sometimes by the incomplete ossification of the internal or sagittal borders of the parietal bones.
Perlis, summarizing these experiments, concludes that: " 1. During labor the cranium undergoes a compensatory change of shape and an ab solute diminution in volume; 2. The modification in form is more marked than the absolute diminution; 3. The vertical diameter is much the most compressed. 4. The smaller transverse diameter is more shortened than the greater; 5. The right diameter is shortened not lengthened; 6. The larger diagonal diameter is reduced; 7. In mensurations, one must always measure the maximum diameter, which always increases; 8. The diame ters elongated in labor return more quickly to their normal size than those which are shortened; 9. The diminished diameters elongate post partum up to the fourth day; 10. The head is more distorted in primipara3 than in multipara; 11. The soft parts chiefly contribute to the distor tion; 12. The longer the labor, after rupture of the membranes, the greater the distortion; 13. Births of boys are more difficult than those of girls." Tarnier and Chantreuil admit the existence of absolute and of com pensatory distortions, the latter predominating.
1. Position O.A.—The head is cylindrical. It is elongated from be hind backward, but diagonally from the chin to the occiput, and flattened transversely and vertically. There is also present the asymmetry of the
two halves of the cranium, due to the depression and flattening of the posterior parietal, described by Dohrn, Barnes and Duncan, the parietal eminences being at different levels.
2. Position 0. P rotation occurs, the only difference between this and the anterior position, is the exaggeration of the depression at the level of the fronto-parietal suture, in anterior positions. If rotation does not take place, or if the occiput remains in the rear, the head is, as it were, drawn vertically from below upward. The crown is conical, constituting the " sugar-loaf head " of Kuneke. The forehead and the parietal bones are on the same plane, as well as the back, the neck and the occiput.
Labat, in 1881, commences by announcing this fact, that, " When one examines the head of a child at term, immediately after its birth, no mat ter what the position, if the labor was spontaneous and the pelvis nor mal, one is struck by two facts: 1. The parietal eminences are not on the same level, whether antero-posteriorly or vertically; 2. One parietal region appears flattened." Subsequently, examining the heads of two children extracted by Porro's operation, by Lucas Championniere and Tarnier, and comparing them with Budin's case, he concludes from their symmetrical shape, that the parietal distortion is certainly the result of labor, i.e., of the pressure experienced by the head in the pelvis. But this symmetry is not properly absolute, and without adopting Stadfeldt's and Schroeder's views on cranial scoliosis, which results from spinal rota tion of the embryo in the ovum, he believes, as do we, that many festal heads are originally asymmetrical, but not regularly so, either in seat or in degree. The following table (see below), borrowed from him, shows the result of his examination of twenty-one children. (The abbreviation N.P., designates the distance separating the root of the nose from the parietal eminences. ) From the table we may conclude that there exists, in both right and left-handed positions, a distortion characterized by general flattening of that parietal region, which, during labor, is in contact with the anterior pelvic wall, and a depression of the parietal eminence on the same side. In a single case, the distortion occurred on the side of the head which was in relation with the posterior pelvic wall. Labat agrees on this point, with Kuneke, and is opposed to Dohrn. Like Duncan, Labat holds that in normal labor, the head is not subjected to any pressure at the level of the promontory. " Very often the head has penetrated, in primipara3, deeply into the pelvis, during the last three months, and during the last fifteen days in multiparm." This asymmetry is only produced at the outlet and at the perineum, as Budin, Depaul, Matthews Duncan and we believe. We hold, with Labat, that this distortion is more marked in proportion, as the labor is long and difficult.