PH YSrOL OG Y OF PAR TURITION. 2 1 7 



common cavity. Every part of the cervix being acted on by the longitu- 

 dinal fibres, the aperture of the os is perfectly circular at this stage ; as is 

 observed in the Cow and Goat when the uterus is pushed back, and its 

 orifice is visible at the vulva. Irregularity in the contractions, however, 

 and particularly when they are rendered so from a transverse position of 

 the fcetus, delays the dilatation, which is otherwise rapid according to the 

 force and frequency of these contractions. At first the dilatation occurs 

 very slowly, especially in primiparse ; when the foetus presents by the 

 croup, or when the body of the uterus inclines too much downwards, 

 causing the cervix to bend up towards the sacrum, it is also very tardy. 

 As soon, however, as the mechanical action of the water-bag and fcetus 

 come into operation, it makes rapid progress in natural parturition. 



If the uterus of animals usually uniparous contains two foetuses, the 

 two cornua are about the same size, each having a foetus in the same 

 position as if there was only one in the uterine cavity. In general, the 

 two foetuses present anteriorly ; although it sometimes happens that the 

 second, or the first, or even both, present posteriorly ; not unfrequently 

 the second makes a malpresentation. When there are twins, parturition 

 is more difficult and slower than when there is only one : possibly because 

 the great distention of the uterus diminishes its contractile power, an- 

 other feature in twin pregnancies is that parturition often occurs before 

 the ordinary time ; and even when this has been reached, one or both 

 foetuses are smaller and weaker than when there is only a single fcetus. 



When twin parturition sets in, the uterine contractions commence 

 almost simultaneously in both cornua, which are much less apart than in 

 the non-pregnant state ; but as the two foetuses cannot be born together, 

 that which is most advanced is delivered first, the other, which is behind 

 it, mechanically aiding in its expulsion. In the Mare, the interval 

 between the birth of twins is rarely more than ten minutes ; with the 

 Cow it may be one or two hours ; and with the Ewe half an hour. When 

 the position of the second foetus is favorable, it is usually expelled more 

 rapidly and easily than the first ; and when they are of a different size, 

 the largest is ordinarily born before the other. W^hen the number of 

 foetuses is greater, they are also expelled successively at intervals of some 

 hours. 



In cases of superfoetation, if such an occurrence can take place in 

 animals other than in those the cornua of whose uterus opens into the 

 vagina, the uterine contractions must be limited to the cornu containing 

 the fcetus whose period for birth has arrived ; otherwise, the other foetus 

 would be expelled at the same time, and there would then be a birth and 

 an abortion. 



With the small multiparous animals, in which the foetuses are expelled 

 one after the other, it may be admitted that each fraction of the uterus 

 corresponding to a fcetus contracts in its turn — at first the segment of one 

 of the cornua nearest the cervix, then the next segment, and so on until 

 the one in proximity to the ovary is reached, so as to get rid of all succes- 

 sively : one cornu expelling a foetus alternately with the other ; the uterine 

 contractions, although general, being most energetic at the portions in- 

 termediate to the foetuses. 



The uterine contractions-are very powerful, as any one can testify who 

 has had occasion to introduce his hand into the uterus during parturition ; 

 and the^r force is not always related to the general physical power of the 

 animal ; though they are always more energetic in the Mare than the Cow, 



