536 Veterinary Obstetrics 



mains for the amnion to be removed from the nose to render 

 respiration possible. 



While normal and easy birth in the large herbivora is virtually- 

 limited to the dorso-sacral position of the anterior presentation, 

 in the smaller domestic animals it is by no means rare for birth 

 to take place easily and safely, for both mother and young, with 

 the fetus in the posterior presentation. 



In the judgment of some obstetric writers, the expulsion of the 

 fetus is more difficult when presenting posteriorly than anteriorly, 

 but we have not been able to verify this opinion. In our expe- 

 rience in the larger domestic animals, the posterior presentation 

 is favorable, in so far as the amount of resistance to expulsion is 

 concerned, provided always that the position of the fetus is dorso- 

 sacral and that there is no deviation of the posterior limbs. 

 When so presenting, the posterior part of the body forms a very 

 elongated cone, which tends to dilate the passages gradually- and 

 causes the fetus to advance with' the least possible difficulty. 

 Some obstetrists suggest that the direction of the hair, being op- 

 posite to that in which the fetus is passing, offers resistance, but 

 it should be remembered that the fetal hairs are very soft and 

 flexible and that, if properly lubricated by the fetal fluids, they 

 offer virtually no obstacle. What little resistance they may the- 

 oretically offer is far more than counterbalanced by the length 

 and regularity of the cone which the posterior presentation fur- 

 nishes. 



However, dystokia is more liable to occur in our larger animals 

 when the fetus presents posteriorly than when it offers anteriorly. 

 The increased tendency to dystokia seems to be be due largely to 

 the tendency for the hind limbs to become deviated from the normal 

 position of extension and one or both of them to be more or less 

 retained beneath the fetal body and thus offer obstruction to 

 birth which cannot be overcome except by obstetric aid. In the 

 mare and cow, also, there is a constant tendency for the fetus, 

 when presenting posteriorly, to assume the dorso-pubic or dorso- 

 ilial position, by which the arc of the fetal body is contrary to the 

 curvature of the genital passage. 



The posterior presentation is undesirable and unfavorable in 

 our larger domestic animals, not because it fundamentally offers 

 serious obstacles to the expulsion of the fetus, but because it 

 tends to imperil the life of the fetus during the act of birth. 



