The oblique direction of the uterus, up wards and forwards, is determined, firstly, by the corresponding obliquity of the pelvis, the plane of whose brim forms with the horizon an angle of 60°. But as the fundus gradually, after three months, emerges from the pelvic cavity, the oblique direction of the uterus is maintained by the symphysis pubis in front, and the sacral promontory behind. Between these, the superior portion of the uterus con tinues to ascend, supported next by the abdo minal walls anteriorly, and the spine poste riorly. The intestines, being bound down by the mesentery, cannot be displaced, and will therefore occupy a position midway between the spinal column and the posterior uterine wall. The pressure of the sacral promontory, and of the lumbar vertebrx, will still give to the uterus a forward tendency, which, on the other hand, will be prevented from becoming excessive by the elasticity of the front walls of the abdomen. If these have not been pre viously much distended, the fundus glides upwards, and ultimately fills the epigastric hollow ; but if the abdominal walls have been nmch relaxed, as by frequent child-bearing, or if the pelvis is much deformed, the fundus uteri is usually turned directly forwards, or even downwards.
At the end of pregnancy, the whole of the fore part of the abdomen is occupied by the uterus ; on either side lie the ascending and descending colon ; the transverse arch, to gether with the ornentum and stomach, fill the space between the fundus of the uterus and the diaphragm, while the rest of the abdomi nal viscera lie laterally and posteriorly to its hinder wall.
Thus it results, that in pregnancy, and espe cially in its last stages, no injurious pressure is exercised, either upon the great vessels, the aorta and vena cava, or upon the intestines, liver, or stomach, whilst the descent of the diaphragm, and, consequently, the act of respiration, is not materially impeded, and space is left for the bItdder and rectum to perform their appropriate acts.
The situation and direction of the pregnant cervix, are necessarily affected by the increase of the principal organ, as well as by its con tents. So long as the weight of the uterus causes it to descend lower into the pelvic cavity, as in the second and third months, the cervix is more readily reached, lying in the lower part of the hollow of the sacrum ; but when the greater part of the uterus lies, as it does at a more advanced period, above the pelvic brim, the cervix is felt with greater difficulty, being more withdrawn from the entrance of the vagina. If the lower segment of the uterus is more than usually spread out, as in transverse presentations, or in the case of twins, or of excessive distension by liquor amnii, then the cervix and os are drawn up so high as sometimes to be quite beyond the reach or an ordinary finger ; or, if the pelvis is very narrow, or the abdominal walls so lax as to cause the falling forward of the womb, the cervix will be equally beyond reach, and in these cases no part of the uterus can be said to be within the pelvic cavity. On the othcr hand, where the pelvis
is unusually roomy, and the vagina and liga ments are lax, the cervix may lie immediately upon the perineum, or even project beyond the orifice of the vulva. In most cases the cervix lies lowest in the pelvis at the earlier and latter periods of pregnancy, and highest about and after the time of quickening. Its projection into the vagina is not always in the direction of the median line, but is more often inclined to the left side, as that of the fundus is towards the right. This obliquity in the position of the uterus may be caused by an unequal length of the ligaments, or more com monly by the projection of the lumbar verte brx, which naturally gives to the body of the organ an inclination towards one or other side.
Alterations in the special coats and tissues, The Peritoneum is that coat which suffers the least alteration during pregnancy, yet the ehanges which it exhibits are not inconsider able. They consist chiefly in a simple mul tiplication of the component elements of the tissue, whereby it is enabled to keep pace with the enormous rate of growth of the uterus, so as still to invest all those portions which were covered by peritoneum in the un impregnated state. During this process of growth, the membrane does not become at tenuated, as would be the case if it suffered mere distension, but its thickness is rather increased, so that the addition of new matter must be in the aggregate very great.
Dr. NV. Hunter imagined that this invest ment of the gravid uterus was accomplished by an unfolding of the layers of the broad ligatnent, for he asserts that, " in proportion as the circumference of the uterus grows larger, the broad ligaments grow narrower, their posterior lamella covering the posterior surface, and their anterior lamella covering the anterior surface of the uterus itself." He arrived at this conclusion from observing the altered relative situation of the appendages, and their appearance of clinging to the sides of the uterus in advanced stages of pregnancy. But the latter circumstance is due to the arch ing of the fundus, already described, which gives to the appendages a downward direction ; while that the broad ligament does not dis appear, as Dr. Hunter asserts, may be shown by measuring the aim, or cutting them off, and comparing them with the salt- e parts in the unimpregnated state, when little or no difference in respect of dimensions will be found between them in the two conditions.