. The science and art of midwifery. t in any sense an active movement. It is always a movement ofaccommodation, the end of which is the successive substitution of ashorter diameter for a previous longer one, so soon as the latter hasencountered sufficient resistance to arrest its further progress. Themechanical advantages of flexion are obvious when we recall that theaverage length of the sub-occipito-bregmatic or maximum diameter ofthe flexed head (three and three fourths inches) is three quarters of aninch less than the occipitofrontal or maximum diameter of the headwhen midway between exten
. The science and art of midwifery. t in any sense an active movement. It is always a movement ofaccommodation, the end of which is the successive substitution of ashorter diameter for a previous longer one, so soon as the latter hasencountered sufficient resistance to arrest its further progress. Themechanical advantages of flexion are obvious when we recall that theaverage length of the sub-occipito-bregmatic or maximum diameter ofthe flexed head (three and three fourths inches) is three quarters of aninch less than the occipitofrontal or maximum diameter of the headwhen midway between extension and flexion. Again, the maximumcircumference of the flexed head (thirteen inches) is one and threefourths inches less than one measured about the extremities of theoccipitofrontal diameter. These measurements, which are represent-ative of the natural state, are, however, far from expressing the fullextent of the differences which exist after the plastic head has under-gone the molding processes incident to labor {vide p. 186).. Fig. 115.—Vertex presentation ; child surrounded by amniotic fluid. (Pinard.) A further advantage of flexion is thus described by Professor Pajot: The foetus, in its entirety, is to be regarded as a broken, vacillatingrod, possessed of mobility at the articulation of the head and trunk ; 180 LABOR. but a solid thus disposed presents conditions unfavorable to the trans-mission of a force acting principally upon one of its extremities ; itfollows, therefore, that previous to flexion the uterine action, pressingupon the pelvic extremity to promote the advance of the foetus, is lostin great measure in its passage from the trunk to the head, by reasonof the mobility of the latter; but the cephalic extremity, once fixedupon the thorax, is most advantageously disposed to participate in theimpulse communicated to the general mass of the foetus.* Now, al-though we have seen that, in its descent through the cervix, the headis for the most part propelled by
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Keywords: ., bookcentury1800, bookdecade1890, bookidsci, booksubjectobstetrics
