As for the third point, the distensibility of the perineum, it is of much importance. Care must be taken lest the compression of the hand against the perineum injure it more than excessive distension. The steady pressure of the hand makes the skin bloodless and fragile. Further the distensibility depends directly on the greater or the less elasticity. This diminishes with age. We notice that the perinea of old primiparie soon lose their elasticity, a loss which can only be taken account of at the time of labor. Statistics show in such women a somewhat relatively longer duration of labor, and a greater frequency of resort to the forceps, and the cause lies at the external genitals. Hecker has found that women who bear their first child after the age of thirty (other authorities place it at thirty-five) suffer laceration of the perineum in 14 per cent. of the cases, while the mean is only 3.66 per cent. The lack of distensibility of the vulva will of course be the greater when cicatrices from one or an other source exist in the labia. Condylomata, varices, and the like, hin der uniform distension, and render rupture a much more dangerous affair. Great cedema, on the other hand, interferes little or not at all with dilatation. Ruptures in general are very frequent, but exact data are not easy to give, since opinions vary in regard to the extent of a rent, which should be called a rupture. The great variations in the statistics prove this. Schroder found laceration in 344 per cent. primiparm, and in 9 per cent. multipane. Winckel noted 11.5 per cent., Olshausen 21 per cent, in case of primipar, and 4.7 per cent. for multipane, which Hildebrandt states as 7.2 per cent. and Hecker as 3.66 per cent.
Very infrequently other conditions favor laceration of the perineum, for example, a deep symphysis, a broad ligamentum arcuatum, deficient pelvic inclination. In each instance the head is pressed more backwards, and this prevents its proper engagement under the symphysis.
On the proper conduct of the labor depends greatly the integrity of the perineum. It is a matter of experience in clinics, that at the begin ning of the session lacerations of the perineum are much more frequent, because beginners conduct the labors, and that such lacerations rarely occur when the delivery is under the personal supervision of the clinical assistants.
Since lacerations of the perineum are of variable import, it is custom ary to divide them into degrees, which, however, are purely artificial. Lacerations to the first degree do not extend to the anus, but within a few centimetres of it (about half an inch). Those to the second degree ex tend to the sphincter ani, and those to the third degree through it. The more extensive lacerations extend a half an inch or so up the rectum it self. In order to make these degrees clearer, Liebmann states the lengths of the tears in centimetres, varying from 1 to 4 ctm. (from .39 to 1.5 inches). It is apparent, however, that the only proper comparison is be tween the original length and that of the tear. The measurements should be taken with the woman in the lateral position.
There are women in whom so many predisposing factors are present, that even the most watchful accoucheur cannot prevent laceration. Those lacerations which occur during spontaneous delivery, where there is ex cessive distension and diminished elasticity extend, generally to the sphinc ter ani. Lacerations to the third degree ordinarily occur during operative
interference. In case of operative manoeuvres, it is right to lay the great est possible stress on watching the perineum, since all resulting lacerations are the result of very extensive stretching.
Lacerations of the first degree affect only the anterior 'Art of the peri neum, including the fourchette and the external skin. The constrictor mini muscle is generally torn at the same time. This may remain in tact, however, if the rent is superficial and only the distended skin is torn. Even in case of a laceration extending to the anus, the skin may alone be torn, this constituting a superficial tear to the second degree. As a rule% however, the underlying tissue is also torn, and the rupture extends as high up into the vaginal wall as it does backward into the perineum. If in a recently delivered woman the labia are pulled apart, the torn surfaces present the appearance of two triangles, one side of which is the torn perineal skin, the second side the vaginal mucous mem brane, and the third side, the bottom of the rent, is common to both. This applies, of course, only to lacerations of the lesser degrees, which involve the skin, the fascia, and the anterior part of the perineal muscles. The complete ruptures or those to the third degree invade the skin, the superficial fascia, the constrictor cunni, the superficial and the deep trans versus perinei, the sphincter ani, and, to a greater or less degree, the recto vaginal septum. According to Hegar's measurements, the rent ordinarily does not extend beyond one half to three-quarters of an inch, exception ally one and a half inches up the rectal wall. The rent in the vagina is frequently greater. It extends not along the mid-line, since the columme rugarum are very resistant, but always to one or another side. It may extend both to the right and to the left, and surround the columme like the tines of a fork. As a rule each tear begins at the posterior commis sure. In case of forceps operations the tips of the instrument may start the laceration higher up, before it is seen at the posterior commissure. Externally also the rent may deviate from the mid-line and extend toward a tuberosity of the ischium, or spread out forked•fashion in front of the anus. The worst and fortunately the least frequent lacerations are the so-called central ruptures of the perineum. When the head extends un hindered, it passes over the centre of the perineum. Lessened inclina tion of the pelvis or deep-set pubic symphysis interferes with this normal method. In case the pressure on the perineum is great and the disten sion marked, the perineum may burst, and the external skin first. The rupture site extends forward and backward and the head appears at the cen tre of the tear. Ordinarily it then happens that the rent becomes com plete, but there are many reported instances where the child was born through the central rupture without tear of the commissure, such as the cases of Elsiisser, Grenser, Stadfelt, Harley, Leopold, Simpson, Birnbaum, Kroner, Liebmann and others. In one case Winckel saw central rupture follow rapid oedema, and in the puerperium gangrene set in.