The principles and practice of obstetrics / by Hugh L. Hodge.

  • Hodge, Hugh L. (Hugh Lenox), 1796-1873.
Date:
1864
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Licence: Public Domain Mark

Credit: The principles and practice of obstetrics / by Hugh L. Hodge. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    three quarters of an inch in front of the Bacro-iliac symphyi ling downward to the extremity of the spine of the ischium, bo as to divide also the infe- rior ith: ligament about one inch and a half from the tubers of the ischia. Of these four sections of the pelvis the two anterior sections are larger than the posterior. (Plate II., Figs. 10 and 11.) The an- terior lateral inclined plane, therefore, extends from the symphysis pubis to the extremity of the spine and to the posterior margin of the plane of the ischium. It embraces, therefore, the whole of the pubis and ischium, including the obturator foramen, and also the descending portion of the ilium below the linea ilia, and a large portion of the inferior sacro-sciatic foramen. The inclination of this plane is double, being from above downward and inward, corresponding to the inclina- tions of the sides of the pelvis already mentioned; and also from behind forward from the transverse vertical section just mentioned toward the symphysis pubis and vulva. The inclination of this plane necessarily varies, at different portions of the pelvis, being slight above, and much greater below, as is represented on the trans- verse sections of the cast. (Plate III., Figs 19, 20, and 21.) The posterior inclined plane extends from the middle line of the sacrum and coccyx to the spine and the plane of the ischium. It is formed, therefore, by one half of the bones just mentioned, a small portion of the os ilium below the linea ilia, the whole of the great sacro-sciatic foramen, all of the superior and part of the inferior sacro-sciatic ligaments. The inclination of this plane is also double; it runs downward from the pro- montory of the sacrum to the coccyx, and also backward and inward from the spine of the ischium to the median line of the sacrum. Although the perpendicular depth of the inclined planes is great, yet, in reference to the rotation of the bead, their length must be estimated by lines drawn from the middle of the sacrum and coccyx to the trans- verse perpendicular section, as shown in the figures just referred to. The posterior plane, therefore, is short as compared to the anterior, and runs in an opposite direction. The anterior planes may be said to look upward, backward and inward, while the posterior planes look upward, forward and inward. The greater length of the anterior planes will explain the fact, already alluded to, that the occiput of the child not only in transverse, but in many cases of posterior oblique positions, will rotate anteriorly under the pubis. Let it moreover be observed that, as the posterior and lateral regions of the pelvis are prolonged by the soft tissues, these inclined planes extend to the middle line of the perineum, and thus continue and perfect the rotation of the head during parturition. Velpeau is among the few authors who describe the line of demarcation between the anterior and posterior planes as passing through the extremities of the spines, of the ischia. He speaks of these planes as forming four triangles,—two on either side,—their bases being above, and their points tending toward each other be- low. This, we have no doubt, is correct. (Plate II., Figs. 10 and 11.) In describing the mechanism of labor, it will be found that the head of the infant descends from the superior strait to the floor of the pelvis very nearly in a straight direction, corresponding to the axis of the superior strait. The top of the head, which was originally par- allel to the superior strait, does not materially alter its direction, until it comes into contact with the coccygeal region. It will be found also that the important pro- cess termed Extension does not commence until the descent, just mentioned, be nearly completed; indeed, that it cannot occur until the top of the head reaches the perineum, and the sub-occipital region passes under the arch of the pubis. To form, therefore, an accurate idea of the passage of the head through the pelvis, its canal should be studied in two aspects, first, as being cylindrical, and second, as being slightly curved ante- riorly. The cylindrical aspect appears in Figs. 5, 6 and 7, on Plate II. The form of the basin of the pelvis has been usually described as conoidal, because the bis- ischiatic diameter is shorter than the bis-iliac. It re- sembles more an irregular cylinder, slightly contracted above, enlarging toward the inferior portion, and very rapidly contracting toward the coccyx. The head of the infant, after leaving the superior pelvis, passes through a series of parallel planes, until it is arrested at the floor of the pelvis. In reference to practice, three or four of these planes should be carefully studied, namely, one at the superior strait, one at the level of the sub-pubic ligament, one at the level of the spines of the ischia, and also one around the coccyx. The First Parallel Plane (Plate II., Fig. 8) of this cylinder is that of the superior strait, which has been already described. The posterior transverse line in the figure designates the line of separation between the anterior and posterior inclined planes of the pelvis. The Second Parallel Plane is drawn on a level with the sub-pubic ligament, and extends backward to the middle of the second bone of the sacrum. We place the second parallel at this spot because the sacrum, although it runs backward to a slight degree at the superior part, nevertheless, remains almost parallel to the bodies of the pubes. The difference between the