524 OBSTETRIC OPERATIONS. 



With animals, the problem is, of course, much less complicated, as 

 their pelvis is somewhat cylindrical ; and its axis — almost rectilinear — 

 can readily be determined by a line passing from the centre of the an- 

 terior circumference to the centre of the vulva, or somewhat towards the 

 middle of the line uniting the two superior ischiatic tuberosities. Saint- 

 Cyr justly points out that traction should be made in the direction of 

 this axis (Fig. 182, A B) ; and that this line of traction, happily for the 

 veterinary obstetrist, and thanks also to the flexibility of the cords which, 

 in his practice, take the place of the forceps, offers no serious difficulty. 

 At page 243, it has been shown that this direction may vary, and may be 

 modified according to the presentation — and more particularly the position 

 — of the foetus, and also according to the period of labor. 



Fig. 182. 

 Diagram of the Pelvic Axis. 



Degree of Traction. 

 When passing through the pelvic cavity, the foetus undergoes a certain 

 amount of compression, proportionate to the uterine contractions or the 

 external traction which determines its progression outwards ; at the same 

 time, this compression produces a kind of reaction in the body of the 

 foetus, and gives rise to an eccentric pressure against the walls of the 

 passage, related to that which itself experiences. The question is, there- 

 fore, limited to the amount of force necessary to overcome the resistance 

 that prevents the onward progress of the foetus, without injuring either 

 the latter or the parent. In veterinary obstetrics we have no fixed data 

 to rely upon ; but the experiments of Joulin, Delore, and Poullet, alluded 

 to by Saint-Cyr, may afford some idea of the resistance offered by the 

 pelvic girdle to the eccentric pressure. These authorities found that if a 

 rounded body — a ball for instance, to represent the head of a foetus — is 

 attempted to be pulled through the pelvis of a woman, it requires a force 

 represented by 375 to 441, and even as much as 635 pounds (estimated 

 by the dynamometer), to produce such serious lesions as fracture in the 

 bones or disunion of the symphyses. But it must not be concluded from 

 this result, that such powerful traction can be practised with impunity in 

 woman. In the first place, the child could not be extracted alive, for its 

 existence appears to be compromised if the degree of traction by the 

 forceps exceeds from 132 to 154 pounds ; and in order that the pelvis of 

 woman could resist such pressure, certain conditions are required which 

 we never meet with in ordinary practice: for instance, the pressure 



