A manual of practical obstetrics . l presenta-tions, or they must be so changed artificially. Mechanism of Transverse Presentations.—There isno mechanism; at least for practical purposes, it may be con-sidered that natural delivery in cross presentations is mechani-cally impossible. Actually, however (so wonderful are Natures resources),there are two processes by which, in exceptional cases, deliverymay occur spontaneously, but they are neither sufficientlysafe nor frequent to be relied upon or waited for in are spontaneous version and spontaneous evolution. Spontaneous Version.
A manual of practical obstetrics . l presenta-tions, or they must be so changed artificially. Mechanism of Transverse Presentations.—There isno mechanism; at least for practical purposes, it may be con-sidered that natural delivery in cross presentations is mechani-cally impossible. Actually, however (so wonderful are Natures resources),there are two processes by which, in exceptional cases, deliverymay occur spontaneously, but they are neither sufficientlysafe nor frequent to be relied upon or waited for in are spontaneous version and spontaneous evolution. Spontaneous Version.—That end of the foetal ovoidnearest the pelvic brim (one end generally is so, for the childsbody lies obliquely across the pelvis, seldom exactly transverse),under the influence of uterine contraction, gets lower andlower, and the other end higher and higher, until, finally, the SPONTANEOUS VERSION. 227 lower end slips over the edge of the brim into the pelviccavity, and the presentation has then become longitudinal, Fig. Chiaras frozen section, representing arrested spontaneous evolution. either a head or breech. This process is most apt to occur inmuciparous women, with feeble uterine contraction, and 228 TRANSVERSE PRESENTATIONS. before rupture of the membranes ; it is sometimes calledspontaneous rectification, those who use this term reservingthe expression spontaneous version for cases in which thatpart of the child directed toward the fundus is turned down-ward to the pelvic brim. This latter proceeding occurs mostfrequently after rupture of the membranes in women withpowerful contractions of the uterus. In this the os uteri isspasmodically contracted, so that while no downward progressof that end of the foetal ovoid nearest the brim can take place(it, on the contrary, glides laterally and upward), that end ofthe child nearest the fundus is forced all the way down to thepelvic brim, and a head or breech presentation results. Fig. 91.
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