PHYSIOLOGY OF PARTURITION. 221 



pregnancy and ends with complete extension in width of that uterine 

 passage. It is marked by increasing uneasiness of the animal : pawing, 

 lying down and rising frequently in a kiud of objectless fashion, while the 

 expression of the physiognomy betrays suffering. When the uterine con- 

 tractions really commence, the creature suddenly stops, as if surprised by 

 the pain ; its eye looks animated and expresses anguish ; the skin is hot, 

 pulse quickened, visible mucous membranes injected ; the abdominal 

 walls are rigid and contracted, the flank is tense, and very frequently 

 fasces or urine are voided. During this pain, if the cervix uteri is ex- 

 plored, it will be found that its attenuated border has a tendency to be- 

 come hard and prominent. When the pain has passed, calm succeeds ; 

 the cervix becomes thick and elastic, and the os is markedly enlarged. 

 Each pain lasts for some seconds to two or three minutes, the interval of 

 quiet continuing to about fifteen minutes at first ; though it diminishes 

 when the contractions become more frequent, more energetic, and more 

 prolonged, and dilatation of the os progresses. Then the fcetal membranes 

 begin to be detached from the inner surface of the uterus and enter the 

 OS, whence they pass into the vagina and between the labia of the vulva, 

 where they appear externally as the "water-bag." In the mean time, the 

 fore limbs and the nose and head of the foetus enter the os, and dilate it 

 to its fullest extent, when the cavity of the uterus forms a canal continu- 

 ous with the vagina. 



3, Expulsion of the Foetus. — The pains become more severe, frequent, 

 and sustained, and to the uterine contractions are added those of the 

 diaphragm, and abdominal and other muscles. If the animal is stand- 

 ing, it brings all its limbs under the body, arches the back, elevates the 

 tail, slightly flexes the hocks, makes a deep inspiration, closes the glottis 

 to imprison the air in the chest, and by a powerful contraction of all the 

 muscles of the trunk, it brings such an amount of pressure to bear on the 

 foetus as to propel it into the pelvic cavity, and rupture the chorion. At 

 leach contraction the " water-bag," formed by the allantois and amnion, 

 ^protruded beyond the vulva, increases in volume. It varies in different 

 fanimals ; being in the Cow about as large as the bladder of a Pig, and 

 tin the Bitch the size of the carp's swimming bladder. When it is very 

 [large in advanced parturition, it is reckoned a good sign ; though it may 

 [not indicate a good presentation of the foetus, nor an easy birth. 



The water-bag soon ruptures, and its contents partly escape ; that 

 [behind the thorax of the foetus being retained, and voided only in small 

 ^quantity as the uterus contracts. When the membranes are thinner and 

 ^weaker than usual, they may rupture before the os is completely dilated, , 

 tand then the fluid escapes in a small quantity at a time \ this frequently 

 ^happens with primiparae, though it is sometimes observed in protracted 

 [labor, which is the most painful. In general, however, no harm results 

 ^from this premature rupture if parturition is not too long delayed ; indeed, 

 iin some cases it may be useful, as when the uterus is over-distended with 

 puid in hydramnios, when its discharge allows the organ to contract more 

 ^freely. In other instances the membranes are remarkably strong and 

 iresisting, and withstand the contractions for a long time after they have 

 [been extruded beyond the vulva ; their artificial rupture may even be 

 trequired. Sometimes they do not rupture at all, and the foetus is born in 

 them, or even after them, as has occurred in the Cow. The rupture 

 lusually occurs at the most dependent part of the bag, at the uterine orifice, 

 towards the os, or in front of it. Then succeeds a brief interval of quiet 



