A textbook of obstetrics . Fig. 223. — Face presentation, chin posterior. 374 THE MECHANISM OF LAHOR. the depth of the pelvis is even greater (5 inches), the delay isabsolute, and such cases can only be terminated by artificialassistance. If the condition is left to nature, there is an effortto force the upper portion of the thorax (9 cm.) into the pelviccavity, along with the posterior half of the childs skull(9^ cm.), for only thus can the chin descend sufficiently to beturned anterior!) under the pubic arch, but it is obviously impos-sible for the bulk of these two diameters to pass through
A textbook of obstetrics . Fig. 223. — Face presentation, chin posterior. 374 THE MECHANISM OF LAHOR. the depth of the pelvis is even greater (5 inches), the delay isabsolute, and such cases can only be terminated by artificialassistance. If the condition is left to nature, there is an effortto force the upper portion of the thorax (9 cm.) into the pelviccavity, along with the posterior half of the childs skull(9^ cm.), for only thus can the chin descend sufficiently to beturned anterior!) under the pubic arch, but it is obviously impos-sible for the bulk of these two diameters to pass through the the chin is posterior, it may rotate to a transverse position, andthen all progress may cease, because the occiput catches on ashoulder and so further extension of the head is prevented (, 226, 227).. Fig. 224.—Face presentation, chin posterior ; enormous elongation of neck. Prognosis.—The fetal mortality of face presentations is 13 to15 per cent. The maternal mortality rises from less than 1 percent, in all labors to 6 percent, or over, if one takes into accountcases of anterior and posterior positions and those which aremismanaged or neglected in general practice. Treatment.—If the chin is directed well forward of the trans-verse diameter of the pelvis, the labor may require no inter-ference. In posterior positions of the chin, however, thecase is always difficult, and demands active treatment. Beforelabor begins, <»r in its early stages, the face presentation may be ABNORMALITIES IN MECHANISM. 375
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