152 



OBSTE TRIG A L PHYSIOL OG Y 



ner for two years. Rainard gives an instance of a. Mare which retained 

 a dead foetus for a year ; the animal was then fecundated again, but hav- 

 ing perished while pregnant with the second foal, an examination of the 

 Uterus was madS, and the two young creatures were found — the first 

 being mummified. 



Death of the foetus in these multiple cases appears to be due either (i) 

 to the stronger vitality of the one which lives, and which, by attracting to 

 itself a larger share of nutriment, starves the other ; (2) to the too con- 

 siderable increase in volume of one foetus, which compresses and atrophies 

 the other ; (3) or to the separation of the foetal from the maternal placentae, 

 which, of course, causes an interruption to the circulation of the young 

 animal, and a suspension of nourishment and the decarbonization of its 

 blood. 



In the second variety of gestation, in which the chorion is common to 

 the two foetuses, but which are yet separated by the amnion, there is only 

 one placenta ; the two having a circulation in common, through their 



Fig. 53. 

 Twin Pregnancy ; 



Cow. 



placentae and the umbilical vessels communicating by their vascular rami- 

 fications. In this case the expulsion of one foetus necessarily brings 

 about that of the other. This also occurs when both are contained in the 

 same envelopes. 



I believe only two instances are on record of inclusion : that of the 

 first mentioned variety, in which one foetus was found in the abdominal 

 cavity of the other, Bartholin, the celebrated anatomist, at the com- 

 mencement of the seventeenth century described the case of a Mare 

 which brought forth a mule, in the abdomen of which was found another ; 

 and Gurlt {Magazin fur Thierheilkunde, 1869, p. 347) mentions an 

 instance in which one foetus was developed within the abdominal cavity 

 of a calf, and consisted of an incomplete left hind leg» a membraneous 



J 



