Extra- Uterine Pregnancy 417 



animals, especiallj' in the sow, and leads eventually to the exist- 

 ence of a group of two or more extra- uterine fetuses, as shown 

 in Fig. 81. 



The cause of the arrest in the migration of the ovum may be a 

 folding in the tube or disease or injury of the mucous membrane. 

 The tendency of tubal pregnanc3' in animals is for the develop- 

 ment to go forward, in a quasi-normal manner, up to that period 

 when the volume of the fetus and its membranes becomes so 

 great that the tube is no longer capable of accommodating them. 

 Then the thin walls of the tube rupture and the fetus or 

 fetuses, with part or all the membranes, pass out into the perito- 

 neal cavity. This rupture and the detachment of the fetal mem- 

 branes may cause fatal hemorrhage. If fatal hemorrhage does 

 not follow, and the fetal membranes have not been wholly de- 

 tached from the maternal placenta in the oviduct, the fetus may 

 become attached to or imbedded in the peritoneal surface, and 

 continue to develop. If its placental attachments in the oviduct 

 have become wholly separated, the fetus necessarily perishes 

 at once and may undergo partial dessication and remain in the 

 peritoneal cavity without injury or inconvenience to the 

 mother throughout her normal span of life. 



In other instances of tubal pregnancy, the developing fetus 

 escapes through the pavilion of the tube and thus gains the 

 peritoneal cavity. It may retain its attachment, through its 

 membranes, with the tube, become adherent to the peritoneal 

 walls and continue until the normal duration of pregnancy has 

 been completed and the usual size of the fetus is reached, when 

 it perishes and probably partially dessicates. 



We do not ordinarily discover tubal pregnane^' during the life 

 of the mother, but only upon post-mortem examination, usually 

 when the animal is slaughtered for food. 



3. Rupture of the gravid uterus may occur at almost any stage 

 of pregnancy, and the possibility of such an accident increases as 

 the clo.se of the normal period of pregnancy approaches. Rupture 

 of the uniparous uterus most readily occurs in its body or the 

 gravid cornu, and the adjacent fetus tends to at once drop 

 through the rent into the peritoneal cavity. In the biparous 

 uterus, the rupture may occur at such a point as to interfere 

 with but one twin, unless the twins have a common chorion, 



