MULTIPLE PREGNANCY 853 



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 generative passages of the mother. 



Multiple Pregnancy. It is not rare to observe two infants at a 

 birth, and cases are on record where there have been four or even five, 

 though in these latter instances they survive usually but a short time, 

 or as is more common, abortion takes place during the first months. 

 Examples of three at a birth have been often observed. 



In cases of twins it is an interesting question to determine 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 the sexes are different. 

 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 foetuses are enclosed in 

 the same amnion. As a rule the two placentae are distinct ; but some- 

 times there is a vascular communication between them, or what appears 

 to be a single placenta may give origin to two umbilical cords. If there 

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

 thought that the two beings are developed from a single ovum ; other- 

 wise it would be necessary to assume that there were originally two sets 

 of membranes which had become fused into one. The instances on 

 record of twins, one white and the other black, show conclusively that 

 two ova may be developed in the uterus at the same time. While there 

 can be no doubt of this, the question of the possibility of the develop- 

 ment of two beings from a single ovum remains unsettled. 



As pathological conditions, extra-uterine pregnancies occur, in which 

 the fecundated ovum, forming its attachments in the Fallopian tube 

 (Fallopian pregnancy) or within the abdominal cavity (abdominal preg- 

 nancy), undergoes a certain degree of development. The uterus usually 

 enlarges in these instances and forms an imperfect decidua. 



Cause of the First Contractions of the Uterus in Normal Parturition. 

 The first contraction of the uterus in normal parturition is undoubtedly 

 referable to some change in the attachment of its contents, which causes 

 the foetus and its membranes to act as a foreign body. When for any 

 reason it is advisable to empty the uterus before the full term of 

 pregnancy, the physiological method of bringing on the contractions 

 of this organ is to separate cautiously a portion of the membranes, as is 



