MULTIPLE PREGNANCY. 941 



At the sixth month, the foetus is from eleven to fourteen inches long and weighs 

 from one and a half to two pounds. If the foetus be delivered at this time, life may con- 

 tinue for a few moments ; the bones of the head are ossified, but the fontanelles and 

 sutures are still wide ; the prepuce has appeared ; the testicles have not descended. 



At the seventh month, the foetus is from fourteen to fifteen inches long and weighs 

 from two to three pounds. The hairs are longer and darker ; the pupillary membrane 

 disappears, undergoing atrophy from the centre to the periphery ; the relative quantity 

 of the amniotic fluid is diminished, and the foetus is not so free in the cavity of the 

 uterus ; the foetus is now viable. 



At the eighth month, the foetus is from fifteen to sixteen inches long and weighs from 

 three to four pounds. The eyelids are opened and the cornea is transparent ; the pupil- 

 lary membrane has disappeared; the left testicle has descended; the umbilicus is at 

 about the middle of the body, the relative size of the lower extremities having increased. 



At the ninth month, the foetus is about seventeen inches long and weighs from five to 

 six pounds. Both testicles have usually descended, but the tunica vaginalis still commu- 

 nicates with the peritoneal cavity. 



At birth, the infant weighs a little more than seven pounds, the usual range being 

 from four to ten pounds, though these limits are sometimes exceeded. 



The position of the foetus, in the great majority of cases, excluding abnormal presenta- 

 tions, is with the head downward ; and why this is the usual and the normal position, is a 

 question which has been the subject of much discussion. As we have just seen, in the 

 early stages of pregnancy, the foetus floats quite freely in the amniotic fluid. Upon this 

 point, Dr. Matthews Duncan has made the following interesting experiments : Securing 

 the limbs of the foetus in the natural position which it assumes in utero, by means of 

 threads, and immersing it in a solution of salt of nearly its own specific gravity, he found 

 that it naturally gravitated to nearly the normal position, with the head downward. It 

 is probable, judging from these observations, that the natural gravitation of the head and 

 of the upper part of the foetus is the determining cause of the ordinary position in utero. 



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 generative pas- 

 sages 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 common, 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 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 they are 

 male and female. In some cases, there are two full sets of membranes, each foetus hav- 

 ing 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 sometimes there is a vascular communication between 

 them, or what appears to be a single placenta 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 



