The common form of extrauterine pregnancy is the Tubal Pregnancy. The ovum may be stopped in any one of the three parts of the tube, and we find Interstitial, Isthmic, or Ampullar Pregnancy. From these primary types, by rupture, secondary forms sometimes arise,--Tubo-abdominal, Tubo-ovarian, and Broad-ligament Pregnancy. The interstitial form, that is, where the ovum is arrested in that part of the tube which passes through the wall of the uterus itself, is the rarest of the tubal pregnancies. Rosenthal (_Ein Fall intranturaler Schwangerschaft. Centralbl. f. Gyn._ 1297-1305) found it in only three per centum of 1324 cases of tubal pregnancy. Some deem the Isthmic variety the commonest. Dr. Howard Kelly (_Operative Gynaecology_) says he never met a case of Interstitial or Ovarian pregnancy in his practice. The interstitial form is especially liable to rupture with suddenly fatal hemorrhage. About one-fourth of the cases of tubal pregnancy end within the first twelve weeks by rupture of the Fallopian tube. If the embryo is implanted in the interstitial end of the tube, the rupture (into the uterus, or into the abdominal cavity, or into the broad ligament) takes place later,--about the fourth month, or even considerably after that time. The reason for {6} the delay here is that the uterus grows with the foetus. If the foetus breaks into the uterus (a very rare occurrence), it is either expelled through the vagina almost immediately or it goes on like a normal pregnancy. Tait was of the opinion that every case of tubal pregnancy results in a rupture of the tube not later than the twelfth week, but this opinion is no longer held. Very rarely a tubal pregnancy goes on without rupture to full term, as in the cases reported by Williams, Saxtorph, Spiegelberg, Chiari, and a few others. Three-fourths, about seventy-eight per centum, of the cases of tubal pregnancy result in what is technically called "tubal abortion" instead of rupture. In tubal abortion the connection between the embryo and the tube-wall is broken by effusion of blood. If the separation is complete the effused blood pushes the embryo out through the fimbriated end of the tube into the abdominal cavity, and then the hemorrhage of the mother commonly ceases. Such an extrusion of the foetus is called a complete tubal abortion. If the connection between the foetus and the tube-wall is only partly severed, the ovum remains in the tube, and the maternal hemorrhage goes on. This is called incomplete tubal abortion. In incomplete tubal abortion the maternal blood may slowly trickle from the fimbriated extremity of the tube into the abdominal cavity, become encapsulated, and thus form an haematocele. If the fimbriated extremity of the tube is blocked, the blood accumulates in the tube and makes an haematosalpynx.