THE EXI'ELLIXH I'OU'Kns IX I'AirrmiTlnX. 229 



does not contain a foetus, and have been noted in extra-uterine 

 pregnancy, when they probably occur through sympathy. They have 

 been observed in the false gestation of the Bitch which has not really 

 conceived, but whose manimic enlarge, and which makes its bed and 

 exhibits other indications of approaching labour ; as well as in preg 

 nancies prolonged beyond their ordinary limit. 



As the uterine contractions which lead to expulsion are usually 

 accompanied by a painful sensation (due to the pressure exercised on 

 the terminations of the nerves within the muscular fibres), they are in 

 common parlance designated "labour pains" {dolores ad j^arttun) ; 

 while the resistance they have to overcome is centred in the foetus and 

 its envelopes, as well as in the passages these have to traverse in order 

 to reach the external world. 



Expulsion is not effected by one contraction, but by a series of con- 

 tractions ; between each of these there is an interval of apparent repose, 

 during which the organ seems to be gathering strength for a new effort. 

 As in almost all unstriped muscular fibres, the reflex action following 

 upon an irritation is slow and gradual, and, according to the degree 

 of irritation, of varying intensity and duration. At the commence- 

 ment, corresponding to the slight irritation, the contraction is feeble 

 and short, and the time required to obtain the necessary sum of the per- 

 sistent irritation for a new reflex action is comparatively long ; though 

 the uterine walls are not relaxed on their contents, but are maintained 

 in a certain state of contraction by the tonicity of their muscles. 



When the pains are regular, there is also a certain gradation in each 

 individual contraction. Feeble at its commencement, it gradually 

 increases, the uterus becoming harder until the maximum of contraction 

 has been reached ; this persists for some time, and then as gradually 

 subsides. 



As parturition progresses, and the separation between tlie uterus and 

 ftt'tus increases, the irritation becomes stronger, and the intervals 

 between the contractions shorter, while these latter augment progres- 

 sively in intensity and duration. The necessity for these intermissions, 

 particularly in the early stage of parturition, is obvious. They allow 

 the animal time to recover, to some extent, from the exhaustion they 

 occasion, and permit the genital passages to become gradually prepared 

 for the exit of the foetus through them ; while the latter can also 

 recover from the inconvenience it may suffer from the interruption 

 between it and the uterus during the pain, and especially towards the 

 termination of the act. 



During each regular pain the whole of the uterus contracts, though 

 the fundus does so most energetically ; and the longitudinal fibres of the 

 organ are more particularly brought into play at the initial and middle 

 stage of parturition. The cornua likewise contract ; they are twisted 

 on themselves anteriorly, are shortened through the action of the longi- 

 tudinal fibres, and are brought nearer the body of the uterus, which is 

 also shortened ; and as this shortening is always taking place in the 

 direction of the cervix, it is here that the sum total of the expelling 

 force is centred ; and it is this force, commencing to operate at the 

 fundus of the organ, and exerted on the incompressible liquor amnii, 

 which gradually opens the os for the extrusion of the foetus. The 

 latter, with its envelopes, first acts as a stimulus to the uterus, but they 

 soon begin to play quite a mechanical part in the dilatation of the 

 already greatly shortened cer\-ix. The latter becomes thinner as the 



