524 



OBSTETRICAL OPERA TIOXS. 



SECTION I.— DIRECTION OF TRACTION. 



Since the forceps was introduced into human obstetric practice, the 

 direction which the foetus should be made to follow in the pelvic cavity 

 of woman has been continually discussed, and has been acknowledged 

 to be a very difficult, as well as a very important problem to solve. This 

 difficulty is mainly due to the fact that the pelvic canal in the human 

 female is not uniform in its dimensions, and that the head of the foetus 

 must pass through it by always offering its gi-eatest diameter to that of 

 the cavity. Consequently, it must execute during its passage a rotation 

 movement in one or other direction, according to the presentation — a 

 movement necessitated by the different planes of the cavity. In addition, 

 the canal is curvilinear, its axis not being represented by a straight, but 

 by a curved line, the form and direction of which are, besides, modified 

 by those deformities of the pelvis that are so frequent and varied in 

 woman, and which constitute one of the principal indications for the 

 use of the forceps. So that the difficulty in the question is to determine, 

 in a rigorous manner, the direction in which to exercise traction with 



Fig. 195. 

 Diagram of the Pelvic Axis. 



this instrument ; though it is generally agreed that it should be made 

 according to the pelvic axis. 



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 hne passing from the centre of the 

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

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

 Traction should therefore be made in the direction of this axis 

 (Fig. 195, A B) ; and 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 

 p. 261 it was shown that this direction can vary, and may be modified 

 according to the presentation — and more particularly the position — of 

 the foetus, and also according to the period of labour. 



SECTION II.— DEGREE OF TRACTION. 



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

 amount of compression, proportionate to the uterine contractions or the 



