The fourth species of extra-uterine pregnancy, which M. Breschet has described as taking place in the substance of the uterus, is of very rare occurrence, four cases only having been recorded by him. (_Med. Chir. Trans._ vol. xiii.) M. Breschet has attempted a variety of explanations of this singular anomaly, but without success; and from the circumstance of the cyst having always been found situated in the fundus to one side, the Fallopian tube of which was closed at its uterine extremity, we think that there can be little doubt of its having been a modification of tubarian pregnancy, where the ovum had been obstructed at that portion of the Fallopian tube where it passes obliquely through the wall of the uterus: in one case the tube appears to have given way at this part, and the ovum to have insinuated itself between the uterus and peritoneum. In these cases the sac ruptured at about the same period as in tubarian pregnancy, except in one instance, where she went five months. A rather inexplicable case of extra-uterine pregnancy has been recorded by Mr. Hay, of Leeds (_Med. Obs. and Inquiries_, vol. iii.,) where a full grown foetus was found enclosed in a large sac, which filled the abdominal cavity, and which communicated inferiorly with the uterus. On tracing the umbilical cord, "we were led," says Mr. Hay, "to a large aperture in the right side of the inferior globular sac already mentioned, from which that which contained the foetus seemed to have its origin. This inferior sac we now found to be the uterus, containing a very thick placenta, which adhered very firmly to about three-fourths of its internal surface, having the navel string attached to its centre, and this centre corresponded nearly with the centre of the fundus uteri. The placenta filled up the greatest part of the aperture of communication between the uterus and sac. The Fallopian tube on the left side was very small; the place of that on the right was occupied by the beginning or orifice of the sac." (_Op. cit._) This would seem to have been a case of pregnancy in the substance of the uterus, and where a portion of the ovum had burst its way into the cavity of the uterus lined with decidua, to which it adhered; the other portion, containing the embryo, distended the uterine parietes in a contrary direction, and thus formed the large sac which communicated with the cavity of the uterus. CHAPTER VI. RETROVERSION OF THE UTERUS. _History.--Causes.--Symptoms.--Diagnosis.--Treatment.--Spontaneous terminations._ During the earlier months of pregnancy the uterus is liable, although rarely, to a peculiar species of displacement, called _retroversion_, in which the fundus is forced downwards and backwards into the hollow of the sacrum, between the rectum and posterior wall of the vagina, and its os and cervix are carried forwards and upwards behind the symphysis pubis.