The ovum when impregnated does not always quit the ovary and pass along the Fallopian tube into the uterus. It may remain in the ovary and become here developed; it may pass into the Fallopian tube and remain there; or from some defect in the action of the fimbriated extremity of this canal, it may escape into the cavity of the abdomen, and become attached to some of the viscera. Hence, extra-uterine pregnancy has been divided into three species, viz. _graviditas tuberia_, _ovaria_, and _ventralis_, according to the situation which the ovum takes. A fourth has been also described by M. Breschet, which he has called _graviditas in substantia uteri_, a modification probably of tubarian pregnancy. [Illustration: _a_ The uterus, its cavity laid open. _b_ Its parietes thickened, as in natural pregnancy. _c_ A portion of decidua separated from its inner surface. _d_ Bristles to show the direction of the Fallopian tubes. _e_ Right Fallopian tube distended into a sac which has burst, containing the extra-uterine ovum. _f_ The foetus. _g_ The chorion. _h_ The ovaries; in the right one is a well marked corpus luteum. _i_ The round ligament.] This singular deviation from the usual course of conception is fortunately of rare occurrence, for few cases terminate favourably. If it be in the Fallopian tube or ovary, these become immensely distended into a species of sac or cyst, to the sides of which the placenta adheres: as the ovum increases, this at length gives way from excessive distension, and the patient usually dies from internal hæmorrhage. In ventral pregnancy, the sac is attached to the abdominal viscera, and is usually imbedded among the convolutions of the intestines: hence the duration of extra-uterine pregnancy will depend upon its situation; thus, if it be in the Fallopian tube, it rarely lasts beyond two months; whereas, ovarian pregnancy will continue for five or six months; on the other hand, in ventral pregnancy the foetus will not only be carried to the full term, but far beyond that period, amounting to several years.[50]