ANOMALIES AND ABNORMALITIES.
First Period.—As there aro oblique vertex and face presentations, so may there be oblique presentations of the pelvic extremity, which give rise to difficulties in the first period, which become greater in proportion as the presentation of the pelvic extremity is less complete. Descent, moulding and flexion of the fcetus will occur more readily in proportion as the component parts of the pelvic extremity are closer together from the onset of labor; and the uterus will exert its force on the fcetus better in proportion as the direction of the fcetus approaches the perpendicular to the plane of the superior strait, that is to say, the axis of the latter Second Period.—Descent of the fcetus always occurs in pelvic presenta tions; but, contrary to what might be supposed, this takes place more slowly when the pelvic extremity is incomplete. One might think, since the incomplete is smaller than the complete pelvic extremity, that it should pass more easily; but it is not so, because the dilatation of the cervix and other maternal parts is not so complete. Engagement, moreover, is diffi cult when the lower limbs are extended on the anterior surface of the fcetus. The most favorable presentation, from this point of view, is when the lower limbs are folded alongside the breech and present with it; this constitutes complete presentation of the pelvic extremity.
Third Period.—The rotation of the trunk may be incomplete, or fail to take place altogether; in fact, it is not indispensable to the disengage ment of the trunk. The volume, and the compressibility of the breech, allow it to clear the external genitals obliquely, nor is this occurrence rare, the rotation of the shoulders commencing only after the delivery of the breech. In proportion as the breech and trunk emerge, rotation is seen to take place externally, corresponding to the internal movement of the shoulders. (See Fig. 219.) The third and fourth periods are, as it were, conjoined. Here, how ever, an irregularity occurs with sufficient frequency during evolution which constitutes the real irregularity of the Fourth Period.—This is the extension of the arms alongside the head.
When the uterine contractions relax, or are insufficient, the arms are no longer closely applied to the thorax, and the resistance they encounter at the cervix, or the lateral pelvic walls, suffices to produce their exten sion, and thus causes serious difficulties. This accident is the more likely to occur from attempts at traction on the breech with a view to hasten the delivery, especially when such traction is made during the intervals between uterine contractions.
Fifth Period. —That of internal rotation of the head is the one in which the irregularities are of the greatest gravity, because they give rise to re tardation in the delivery of the head, and as the trunk is delivered, the life of the child may be greatly jeopardized. These irregularities may be divided into three classes : 1st. The rotation of the head may take place; but instead of remaining flexed, the head extends, and the chin is arrested behind, either at or below the level of the sacro-vertebral angle. 2d. Rotation does not occur, and instead of again coming to the front, the head remains behind; or else rotation, instead of failing to occur, takes place directly backward in the occipito-sacral direction, when again two conditions may be present—the head is flexed, or it is extended.
It is evident that each of these anomalies usually require the inter vention of the obstetrician, and the sixth step, the delivery of the head, becomes artificial. In some cases, however, the head emerges unaided, despite the difficulties it encounters. Let us examine these different cases, and we will confine ourselves here to those in which intervention is called for, leaving the description of the manipulations to the section on treatment of breech presentation.
1st. Rotation extended; chin arrested behind; in tervention.