The membranes when too thick or tough (Merriman's _Synopsis_, p. 217,) may retard the labour occasionally, especially during the second stage, when instead of bursting and allowing the uterus to contract more powerfully upon the child by the evacuation of the liquor amnii, they are pushed down into the vagina, forming a large conical sac, which may even protrude externally. We doubt much, however, if the non-rupture of the membranes at the proper time during labour is of itself sufficient to retard its progress, for it is frequently observed that the head will, nevertheless, advance rapidly and even be born covered by the protruded membranes. Where labour is rendered tedious by the unusual strength of the membranes, it is generally connected with considerable distention of the uterus from liquor amnii; in which case the bag of waters is so spherical that it will not descend readily into the vagina, even although the os uteri is fully dilated, and, therefore, prevents the advance of the head: to this we shall recur immediately. So long as there is no undue accumulation of liquor amnii, we may safely allow the membranes to descend to the os externum before we rupture them. In former times a variety of instruments were employed for this purpose, many of which were dangerous, and all unnecessary, the finger being in most cases sufficient. The most effectual way of doing this is to press the thumb and middle finger upon the membranes during a pain and thus increase their tension, whilst the point of the fore-finger is pushed against them: scratching them with the nail during a pain will be sufficient when they are higher up the vagina. _Premature rupture of the membranes._ More frequently the membranes rupture too soon, that is, before the os uteri is fully dilated: this may arise from their being too thin, a condition, however, which it is not very easy to prove: in most instances, it is observed where the uterus is but moderately distended, and where it has that oval or pyriform shape which we have already pointed out as being best adapted for acting efficiently upon the os uteri. This, perhaps, is one reason, why too early rupture of the membranes so frequently occurs in primiparæ; and this may be one cause, among many others, why first labours are generally so much more tedious and severe. The membranes may also be prematurely ruptured by violent exertions, coughing, sneezing, vomiting, &c. by straining immoderately and too soon, by rough and awkward examination, &c. Where this is the case, the patient should preserve the horizontal posture, and keep as quiet as she can until the os uteri has dilated sufficiently and allowed the head to advance.