Obliteration of the cervix does not always cause opening of the cervix; and, in primiparte, it may be obliterated, while the external os is closed until labor pains come on.
All agree that the cervix is obliterated from above downwards;—and Tarnier and Chantreuil were wrong in ascribing to me the opinion that in multiparx the reverse was the case. They allude to a statement of Stolz:--" In the first pregnancy the cervix disappears from within out; in subsequent pregnancies from without in." Our opinion is that it always begins at the internal os. But as in multipane the external os is often large, it might seem that obliteration began here: hence the error.
Tarnier and Chantreuil state that when, during labor, the cervix has to be cut, it is the external, and not the internal os that is incised; and Pajot states that when, after delivery, the cervix returns to normal, it is at the internal os that the changes first begin.
Stolz thus describes obliteration:—" The two ora of the cervix go to meet each other, the middle of the cervix increasing in width thereby. The internal os opens, and the cervix merges with the inferior segment of the uterus, and all that remains of the cervix is the external os.
" In multiparm the external os is deep, round, basin-shaped, somewhat open, and allows the introduction of the finger. And thus, in multiparte, the cervix disappears from without in." We do not share this opinion; but regard obliteration as always occur ring from above down.
Once this operation completed, the uterus consists of a single cavity closed by the os externum, which is often difficult to determine in primi pane. But in multiparas a groove can be felt.
Tarnier states that " the lower segment of the uterus is represented by the cervix, the thin walls of which are stretched in the form of a sebilla whose diameter is about 4 inches. Painless contractions of the uterus are the causes of this obliteration, which progresses from above down, while softening is from below up." Braune, Muller, Birnbaum, Lott and Bandl have lately studied cervical changes during pregnancy. Braune made autopsies in cases of death during the later months of pregnancy, and found the cervix 4.2 inches long anteriorly and 3.9 inches posteriorly. This increase was at the ex pense of the lower uterine segment. (See Fig. 79). Muller admits the conservation of the cervix until the end of pregnancy, even until the be ginning of labor. In most cases he says, when the head is engaged, and the cervix admits the finger, which can touch the membranes, we find, in primiparre, that the finger does not immediately reach the membranes and the head, but is separated by a space of to 11 inches.
At the apex of this space is the os internum, through which the mem branes may be felt. Here there is a muscular ring like a sphincter, and when the finger passes this it finds the walls of the uterus flaccid.
This wall, which is in immediate contact with the head, Muller says is formed by a kind of invagination of the uterine wall and by the anterior wall of the cervix. Hence the projecting muscular ring above described.
According to Muller, the descending head pushes before it into the pel vis the anterior wall of the uterus, and is thus in a pouch in front and underneath the os internum, which is formed by the lower segment of the uterus. The cervical canal is thus about .78 to 1.17 inches long. Bandl observes that this canal, having a length of .78 to .9 inches, and which he has always found to have thin walls when the head was low down, does not correspond to the size of the virgin cervix, which measures 1.36 inches. (Henle and Luschka). And since no one has proven oblitera tion of the cervix during pregnancy, but, rather, an increase from en largement of, and additions to, its primal elements (Muller—Lott), as well as softening of its mass, the above cannot be explained except by changes occurring during pregnancy.
Lott recognizes the isthmus of Muller, but says it is formed by the an terior portion of the lower segment of the uterus, the anterior wall of the cervical canal, by the region of the internal os, and even by the lower portion of the posterior wall of the uterus. • There is not a true invagination of all the anterior wall of the lower segment of the uterus and of the cervical canal, but only of their mucosa, and a portion of their stroma. Bandl accepts Lott's statements: Mul let's ring is only accidental, that is, a fold of the vaginal wall of the cervix between the cervix and the head. The internal os of Muller is only ficti tious, and the tissue of the cervix is absorbed by the lower segment of the uterus. Bandl, agreeing with Braune and Martin, describes the event as follows (see Fig. 80):—The cervix lengthens during the first six months of pregnancy: but in the last ten weeks it shortens, the lower segment of the uterus widening and thinning, and it helps to form a canal—the cer vico-uterine,—destined to replace the cervical canal; this, Branne's canal, is for lodging the foetal part after its engagement. The canal has three orifices. The lower, (the external ring,) is the os externum, about which all authors agree. The middle,—the internal os of former authors,—or the isthmus of Muller, is made by a kind of invagination of the vaginal wall of the cervix, the last trace of the os internum, which disappears at the end of pregnancy when it is absorbed by the lower segment of the uterus. At this point the cervical mucosa disappears, gliding over the muscular layer, forming folds so that the os internum approaches the os externum. Below the remains of this os internum the widened portion of the lower segment of the uterus forms a thin-walled cavity, the true canal of Braune, limited below by Miiller's isthmus, or os internum, and above, at its junc tion with the body of the uterus, nearly on a level with the peritoneal vesico-uterine cul-de-sac, by a thickening of the wall and a ring-like pro jection of that wall, Bandl's ring.