It has been supposed by many authors, especially Dr. Burns, that distension of the bladder is, in many instances, the immediate cause of retroversion, owing to the intimate connexion which exists between the lower part of the uterus and this organ, inasmuch, "that whenever the bladder rises by distension, the uterus must rise also." In the later editions of his work on the principles of midwifery, he has considerably modified this opinion, and from careful examination of the parts in situ, in the third month, is not disposed to consider the distension of the bladder as the cause, but the effect of retroversion. In every case which has come under our own observation, the bladder has not been distended until the retroversion had taken place, in consequence of which the os and cervix uteri had been tilted up behind the symphysis pubis, and having thus compressed its neck had caused the difficulty in passing water.[52] Whenever any force is applied to the fundus uteri at this period of pregnancy, either from external violence, or the action of the abdominal muscles pressing the intestines and bladder against it, it will be pushed against the rectum, in which case the rectum will be flattened at that part against which the fundus rests; and if any mass of fæculent matter be passing along the intestine, its course will be obstructed at this point, and the rectum quickly become distended with an accumulation of fæces above, by which means the fundus will not only be prevented from rising, but in all probability be forced still lower down. If the force which has originally pushed the fundus backwards be of sufficient degree and duration to carry it past the promontory of the sacrum, the increase of space which it will meet with in the hollow of the sacrum, and the straining efforts which are induced by the displacement itself, contribute powerfully to complete the mischief, and to bring the fundus so low into the pelvic cavity as at length to turn it nearly upside down. As soon as the fundus of the uterus is pressed with any degree of force against the posterior parietes of the pelvis, its os and cervix will be directed forwards and upwards against the symphysis pubis, and from the pressure which they exert against the neck of the bladder, the patient either experiences complete retention of urine, or, at any rate, considerable difficulty in passing it; hence, therefore, we find, that where retroversion has come on suddenly, the patient is generally sensible of the pain produced by the displacement, before she has experienced any difficulty in evacuating the bladder.