MULTIPLE PREGNANCY. 451 



The shape of the uterus at full term is ovoid, the lower 

 portion being the narrower. The foetus has the head slightly 

 flexed upon the sternum, the arms flexed upon the chest and 

 crossed, the spinal column curved forward, the thighs flexed 

 upon the abdomen, the legs slightly flexed, and usually crossed 

 in front, and the feet flexed upon the legs, with their inner 

 margin drawn toward the tibia. This is the position in which 

 the foetus is best adapted to the size of the uterine cavity, 

 and in which the expulsive force of the uterus can be most 

 favorably exerted, both as regards the foetus and the genera- 

 tive passages of the mother. 



Multiple Pregnancy. It is not very rare to observe two 

 children at a birth, and cases are on record where there have 

 been four and even five, though in these latter instances the 

 children generally survive but a short time, or, as is more com- 

 mon, abortion takes place during the first months. Three at 

 a birth, though rare, has been often observed ; and we have 

 in mind at this moment a case of three females, triplets, all 

 of whom lived past middle age. 



In cases of twins, it is an interesting question to deter- 

 mine whether the development always takes place from two 

 ova, or whether a single ovum may be developed into two 

 beings. In the majority of cases, twins are of the same sex, 

 though sometimes they are male and female. In some cases, 

 there are two full sets of membranes, each foetus having its 

 distinct decidua, placenta, and chorion ; in others, there is a 

 single chorion and a double amnion ; but, in some, both foe- 

 tuses are enclosed in the same amnion. As a rule, the two 

 placentae are distinct ; but sometimes there is a vascular com- 

 munication between them, or what appears to be a single pla- 

 centa may give origin to two umbilical cords. If there be 

 but a single chorion and amnion and a single placenta, it has 

 been thought that the two beings are developed from a single 

 ovum ; otherwise, it would be necessary to assume that there 

 were originally two sets of membranes, which had become 



