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FIG. 6.

it is arrested because a fully extended head cannot be further extended, therefore there is no more possibility of forcing the face around the angle into the vagina than there is of forcing a stiff straight stick through the elbow of a stove pipe. (See Fig. 7. )

In breech cases the same forces are at work in the same manner as in head cases. The breech is forced straight down to the floor of the pelvis, rotation occurs, the hips are gradually forced around the uterovaginal angle, the body is bent laterally, the shoulders rotate and pass the angle while the neck is bent, the head rotates turns the angle by flexion, and the child is born. When the after-coming occiput rotates posteriorly, the head may be delivered either by extension or flexion, as the case may be. In either case the uterine contractions cause the head to glide over the smooth surface of the sacrum, the head and sacrum resembling, for the time being, a ball-and-socket joint. Proof that the child passes through an angular instead of a circular canal is found in the fact that in breech cases, when the legs are extended over the abdomen, labor is greatly delayed for the reason that the legs cannot be bent

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laterally, consequently there is much greater difficulty in bending the body laterally sufficiently to allow it to pass the angle, the legs acting somewhat as a splint.

In King's "Manual of Obstetrics" is a cut showing an arrested spontaneous evolution, in a transverse presentation, which beautifully illustrates the utero-vaginal angle. In such a case it would, of course, be impossible to deliver the child. (See Fig. 8.)

I shall not speak of the management of labor, as that remains unchanged; but several questions have suggested themselves to my mind, to which I should like to direct your attention: First. In a forceps delivery, when the head is at the superior strait we should make traction in the line of the axis of the uterus until the pelvic floor is reached, this being done by grasping the shank of the forceps with the left hand at the vaginal orifice, while the right grasps the ends of the handles and lifts them up, thus making the right hand the power and the left hand the fulcrum, the child's head being the resistance, as described by Pajot.

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In this way no power is lost; while if we make traction in the direction of the curve of the sacrum, power is lost, as the child's head will, to a certain extent, impinge on the pubes. As soon as the head reaches the utero-vaginal angle, traction should be made in the direction of the vaginal axis.

Second. Is not the birth of the child through the anus (a most unfortunate and distressing accident that has sometimes happened) rather strong proof that there is an angle in the canal, and that the uterine contractions were so strong that the head had not sufficient time to pass the angle and was forced in a nearly straight line through the soft parts ?

Third, Is not the fact that, when the head has reached the floor of the pelvis, the pain increases in severity, the head advancing with a pain and receding upon its cessation-extending and flexing, gliding over the smooth sacrum-evidence against a curved-canal theory? For if the canal were circular there would be no arrest of progress, any more than there is in the rectum. The apparent curving of the vaginal canal is simply the distention of the perineum to adapt it to the contour of the child's head.

Fourth. When the head is about to emerge from the vaginal orifice, the lower part of the woman's abdomen is much more prominent than at any previous time, because the head and body are at right angles with each other, the head being extended or flexed as the case may be; and if the case be occipito-anterior, the child's face may be felt through the perineum.

The question might be raised that it is impossible for the head to be delivered by simple extension or flexion, as the neck is not long enough to reach from the utero-vaginal angle to the vaginal orifice. This can be answered by giving the length of this portion of the canal, which in the parturient woman measures from one to one and one-half inches.

Do the bones of the pelvis exert the influence on the mechanism of labor that they are credited with? This question may seem entirely uncalled for, but let us consider a moment. The pelvis is a bony ring supporting the trunk, and in turn supported by the legs. It is shaped to give strength and elasticity to the entire body, and to accommodate, in the female, the uterus and its appendages, the rectum, and the bladder. That it exerts but slight influence on the mechanism of labor is shown by the thickening of the interarticular fibro-cartilage and the movability of the pelvic articulations, so that when the child descends the bones may be seperated a little, or, in other words, that they may, to a certain extent, be pushed out of the way. The hollow of the sacrum does not cause the head to advance toward the vaginal outlet, for the reason that the shape of the head corresponds to the shape of the anterior surface of the sacrum, and when the head reaches the floor of the pelvis it fits into the sacrum, exactly as the head of the femur fits into the acetabulum, and the sacrum, like the acetabulum, furnishes a smooth socket in which the head moves, governed by the uterus above and the utero-vaginal angle below.

To sum up in a few words my theory of the mechanism of the labor; The head starts in the oblique diameter of the pelvis, descends in a straight line through the uterine axis to the floor of the pelvis, where it comes in contact with the levator ani muscle trough and rotates into the antero-posterior diamater. When it reaches the bottom of the trough

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it stops, as it can go no further in that direction. Then extension begins the occiput is forced around the utero-vaginal angle until the head is fully extended, by which time the occiput emerges under the pubes, and immediately afterwards the head is delivered. Meanwhile the shoulders come down, rotate, are forced around the angle, the body is bent laterally, and the shoulders are delivered; and in the same manner the hips are delivered.

After delivery of the placenta the parts resume their former relations, and with the exception of the enlarged uterus, appear as they did before pregnancy. (See Fig. 9.)

In the preparation of this paper I consult the works of King, Lusk, Playfair, Parvin, Skene, Dickinson, Thorburn, and Gray, and wish at this time to make acknowledgment of the fact.

I am indebted to William Woods & Co., Medical Publishers, New York, for the cuts illustrating the article.

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