ANOMALIES IN THE MECHANISM OF FACE PRESENTATIONS.
Irregularities in the mechanism of face presentations are more liable to occur than in vertex cases, and are manifested in the different periods.
First Period. —The anomalies of this stage are better called deviations from or varieties of the regular face presentations. Thus, in the frontal variety, the brow remains, for a long time, in the centre of the pelvis; in the mental variety, the chin presents. Again, the face is inclined toward one or the other check, constituting the malar variety. All these varieties are corrected during labor, but sometimes the first period results in flexion, and not in extension. Then the forehead ascends, the occiput descends, and the face is transformed into a vertex case. This is, of course, a very favorable termination.
Second Pcriod. —Descent is governed, as already stated, by the length of the neck, the size of the foetus (which is generally large in face cases), the intensity of the pains and the inclination of the presentation, all of which occasion an infinite variety.
Third are most frequent in this stage, and are here of great importance, for rotation must occur in order that expulsion of the head may follow. If rotation does not take place, we may almost abso lutely say that spontaneous labor is impossible and intervention necessary. Intervention must often be heroic, involving the application of the for ceps and of the cephalotribe. Some authors have, however, cited cases in which labor terminated spontaneously, although rotation had not oc curred. Velpean, who admits a mento-sacral variety, says that the fore head advances to the symphysis, while the chin descends beneath the promontory. The head thus engages in front, as far as just beyond the bregma, and behind, so far that the front of the neck and the upper part of the thorax also enter the pelvis. The diameter 0.M. then revolves, from above downward and from behind forward. The chin, penetrating the pelvis, more deeply, and retained by the thorax, which can not ad vance, forces the sagittal suture to slip behind the pubes, and the brow to move to the upper part of the outlet. The frontal eminences get a pur chase upon the perineum, the posterior fontanelle descends, in its turn, appearing at the summit of the arch, and the head escapes as in the occipito-anterior position. With Cazeaux, from whom we borrow this quotation, we call attention to the fact, that the longest diameter which must pass through the pelvic diameter, A.P., is not the diameter 0.F., as Velpeau says, but 0.M., which is impossible. This invalidates Vel peau's explanation.
Guillemot admits two terminations: 1. The brow descends until the anterior fontanelle appears beneath the symphysis, when the chin can advance and reach the anterior perineal commissure. As Cazeaux says, it is necessary in order that this be possible, that the thorax and head en gage together, which is impossible unless the fcetus be very small. ( ride
Fig. 211). 2. The face presentation is changed to a vertex presentation. This change, since Guillemot supposes the face to be deep in the pelvis, requires the revolution of the diameter 0.M., which is impossible. Ca zeaux states that, in these cases, the chin, in the position 31.I.R.P., is pushed to the level of the great sacro-sciatic foramen, and there causes depression of the soft parts. This depression will augment the oblique diameter .23 to .31 inches,and will permit the diameter 0. M. to revolve and the head to be flexed, which will bring the occiput below the symphysis. The face is thus changed to a vertex case. This is Dubois's explanation, adopted by Tarnier and Chantreuil, except that these authors hold that the chin forms a hollow for itself below the sciatic ligament, on the peri neum, which permits of the transformation of the face to a vertex case. Chailly, who admits the mento-sacral position of Velpeau, assumes the descent of the chin to below the coccyx, the depression of the soft parts, the rotation of the diameter 0. M., and the transformation into a vertex presentation. The anomalies of the fourth, fifth and sixth periods are the same as in vertex cases.
prognosis of face presentations is, therefore, always grave, and if the early writers exaggerated matters in considering sponta neous labor in face cases impossible, Madame Lachapelle fell into the op posite error in saying: " After all, I affirm that, of two patients of equal power, of equally large passages and of similar genera', circumstances, the one whose child presents by the face will, at least, be delivered just as easily as the one whose child presents by the vertex." Dilatation is slower, the uterine force is less easily transmitted to the fcetus, labor is always much longer, intervention more often required, and the conditions less favorable for the mother. The dangers to the child are much greater. Aside from the cases where, the forceps being inadequate, embryotomy is demanded, the child often dies during labor. While, in vertex cases, the mortality, according to Schroeder, is only five per cent., it is thirteen per cent. in face cases. The frontal variety is the most dangerous. Accord ing to Massmann, Hecker and Stadfeldt there wore twenty-one deaths among forty-one children. Ahlfeld, however, thinks the prognosis of this variety the most favorable. On the one hand, compression of the neck, produced at the cervix, at the inlet, and particularly at the sym physis, causes cerebral hyperaemia and even cerebral hemorrhage. On the other hand, Tarnier and Chantreuil show that, in face presentations, the cord may be compressed, either because prolapsed (6.3 per cent. in face cases, and 1.8 per cent. in vertex cases, according to Hugenberger), or because, if loops exist, the Tunis may be compressed between the occi put and the neck.