Vertex Presentations, with Extension of the Head.
Although formerly considered so dangerous as always to require active interference, face presentations were regarded by Mme. Lachapelle not only as harmless, but almost more favorable than presentations of the vertex. This is far from being the case, and, without going as far as did the older authors, it can safely be said that the presentation is a trouble some one for both mother and child. It is the rarest of all the presenta tions: thus in 15,652 births, Mme. Lachapelle only found it 72 times, and in 81,711 births, Pinard only found it 330 times.
In 7835 births at Vienna Ntege16 found it 44 times.
gi 8514 " " Prague and 58 " " 7104 " " Gottingen Grenser " 39 " " 16232 births Depaul found it only 93 times.
" 8212 births at Munich, Hecker found 49 face and 7 fore head presentations.
It was formerly supposed that all face presentations were secondary, that they were only transformations of vertex presentations that occurred during delivery.
Mme. Lachapelle was the first to prove that there was such a tiling as a primitive face presentation, existing as such before labor began at all. Her observations have been confirmed by those of NaegeY, of Depaul, and of Spiegelberg. Nevertheless, secondary presentations of this kind are much the more frequent.
Many different causes have been invoked to explain face presentations. We must refer the curious reader to the works of Hecker and Buhl, of Freund, of Ahlfeld, and of Winckel. The latter has enumerated not less than thirty-three different ones.
It was long believed that uterine obliquity was the cause of face presen tations. First proposed by Deventer, this explanation was accepted by Baudelocque, Michaelis, Mme. Lachapelle, Winckel, and Matthews Dun can.
The latter says that, in ordinary labor, where the vertex presents, whether the occiput be directed to the right or to the left, the change to a face presentation is prevented by the greater length of the arm of the anterior lever of the head. Pressure from abOve, when the longitudinal axis of the uterus coincides with the axis of the superior strait, causes flexion of the head. But when the posterior arm of the lever is the
longest, extension of the head, and a forehead presentation results, the first step towards a face presentation. The part of the pelvis where this occurs has a rectilinear axis, except where there exists a slight inclination of the uterus to the right. This frequent right inclination of the uterus determines, at the level of the superior strait, a curve of the genital canal, the concavity of which is directed to the right side.
In the great majority of cases of right lateral inclination of the uterus, the occiput occupies the concavity of the genital curve at the level of the superior strait. If the head encounters much resistance, the occiput tends to descend first, from the relative shortness of the arm of the pos terior lever; and since it is placed nearer the concavity of the canal, it is nearer to the axis that represents• the resultant of forces, an axis which, from the right lateral 'deviation of the uterus, runs from above downward, and from right to left. The vertex presentation will then persist. In a certain number of cases, about twice in seven times, the occiput ap proaches the right side of the pelvic canal, the convex side, while the forehead touches the left and concave side of the canal. The resultant of the forces will tend, of itself, to make the forehead descend. This ten dency of the forehead to descend instead of the occiput will be, in most cases, successfully resisted by the soft parts, which oppose the descent of the anterior part of the head, the length of the arm of the anterior lever being much the greatest. But in a case where the lateral inclination of the uterus is exaggerated, this resistance is overcome, and the forehead descends. In cases where the head is dolicho-cephalons, the resistance of the arm of the anterior lever of the head will be diminished, and in some cases will be entirely annihilated. The forehead is then obliged to descend first, and extension will occur.