The cervical mucous membrane, which is retained*, after labour exhibits here and there sometimes slight lacerations, extending occa sionally into, or through, the proper tissue of the part. In other respects, the internal aspect of the cervical canal resembles that of the same part in the last month of gestation, ex cept that the large and voluminous plicm (fig. 446.) have becoine folded out and flattened during the previous act of labour. Around the margin of the internal os uteri may be seen a thin ragged fringe marking the point from which the decidua, here usually much attenuated, had been torn away.
The entire uterine cavity is denuded ; it presents everywhere, except at the placental space, a rough, flocculent, and sometimes honeycomb-like surface, caused by the de tachment of a portion of the decidua and its discharge along with the fcetal membranes. Another portion remains covering the mus cular structure of the uterus, but is in parts so thin, that the latter appears to be left nearly bare.
The surface to which the placenta had been attached forms usually one-third of the entire inner superficies of the contracted uterus. This, which is termed the placental space, is easily distinguished by its uneven, rugged, and somewhat nodulated appearance; caused chiefly by the presence of' numerous large veins, whose truncated orifices obstructed by coagula here protrude slightly above the general level.
Upon section, the uterine walls exhibit everywhere the same laminated arrangement of the proper tissues, with numerous inter mediately lying tortuous arteries and flat tened veins and sinuses, already described as observable in the uterus during the latter pe riods of pregnancy ( fig. 449.).
These flattened thin-walled veins are usu ally empty, or contain a few unadherent coa gula. Those, however, which occupy the seat of attachment of the placenta, where they are much larger than in any other situation, are filled with dark or greyish-red clots adherent to their walls, and closing their mouths, which tertninate directly upon the uterine cavity.
The peritoneal coat of the recently emptied uterus is of a pale pinkish-white colour, and presents a smooth, shining, and in parts a slightly wrinkled surface. It is thicker and less diaphanous than the same membrane be fore labour.
The process of involution. — No rapid or material alteration in the size or composition of the organ occurs during the first few days after labour. In the course of the first week, however, commences.a series of important and interesting processes, continued during the greater portion of the two months imme diately following labour, and having for their object the restoration of the uterus to a con dition similar to, though not identical with, its state before impregnation. These changes consist in a gradual diminution in the weight and dimensions of the organ accompanied by a corresponding metamorphosis and ultimate reconstruction of its tissues. They together constitute the process commonly termed the involution of the uterus, which will now be examined.
Changes in dinzensions and weight.—Accord ing to repeated estimates made by Heschl, the weight of the uterus, immediately after labour, ranges from 1 lb. 6-7oz., ordinarily, to 2lbs. 5-7oz.; the latter being the weight after twin labour.
The dimensions depend upon the degree of contraction. Under ordinary circumstances, the entire length is 8-10 inches, and the thickness of the parietes 1 inch. These first changes in the dimensions of the organ, as compared with the state previous to labour, are effected solely by the contraction of the uterine fibre. They consist chiefly in a re arrangement of relative position in the com ponent tissues, by which, while the entire substance of the uterus remains undiminished, its length and breadth are greatly- reduced, and the thickness of the parietes correspondingly increased. In one respect, however, the en tire bulC and weight are less than they were before labour, because a much smaller quan tity of blood now circulates in the walls, but the solids remain unaltered.
At the end of the first week, the diminution of the organ is not very considerable. Its weight is merely reduced from 1lb. 6-7oz. to 1 lb. 3-4oz. At the end of the second week, the rate of diminution is found to have been much more rapid ; the organ now weighs only 10-11oz. At the end of the fifth week, 5-6oz.; and in the course of the second month, it is reduced to its ordinary weight of 1/ to 2/ oz.; but it never entirely regains the small size and dimensions characteristic of the virgin state.