CAUSES OF THE POSITIONS.
Vertex. —Spiegelberg has observed that the position of the head de pends upon the conformity of the uterus to the pelvis. The back of the child is placed at one side of the uterus, and the head has its long diam eter in the longest (transverse) diameter of the inferior segment of that organ. If this transverse diameter and that of the superior strait are parallel, the sagittal suture will descend transversely. If, on the other hand, the transverse diameter of the uterus is in the direction of an oblique pelvic diameter, the head will enter the superior strait in the di rection of the oblique diameter. For the fundus uteri is most frequently inclined to the right, and the entire organ has a movement of rotation on its longitudinal axis, which brings its left side nearer the anterior abdomi nal wall than the right side. Therefore, on this left side must descend the heaviest part of the fcetal anterior extremity, which is the posterior half of the head, and of the back. (Ntegele and Grenser). Hence the
greater frequency of OLA.
Tarnier and Chantreuil coincide in this opinion. They claim that, in consequence of uterine obliquity and the prominence of the sacro-verte bral angle, the fcetal ovoid accommodates itself better to the shape of the uterus when the back of the infant is turned to the left and in front, and the flexed head is plunged into the lesser pelvis. As to the right posterior position, accommodation is still easy upon condition that the head extends slowly when it engages deeply in the pelvis.
positions of the face correspond to right positions of the head, and are explainable in the same manner. It is the same for the breech.
As to trunk positions, they are only deviations from vertex or breech positions, and are distinguished only by a greater difficulty of accommo dation.