534 Veterhiaty Obstetrics 



pubis of the mother, or there occurs the dorso-pubic position. 

 This position of the fetus is such that birth cannot usually take 

 place without assistance and may consequently be regarded, for 

 all practical purposes, as abnormal. In both the dorso-ilial and 

 dorso-pubic positions, numerous deviations or misplacements of 

 any or all extremities may occur and add to the complications 

 and difficulties of the expulsion of the fetus. 



We have already stated that the fetus normally lies en arc or 

 curved somewhat ventralwards. The anatomy of the fetus pre- 

 vents this curvature from being readily reversed, and consequent- 

 ly this curve of the body should always correspond to whatever 

 curvature exists in the birth-canal. A study of the genital pas- 

 sage of the mother will show that this curvature, in the main, is 

 concave above and convex below. Consequently, if the curved 

 body of the fetus is to pass readily through the canal, it must 

 present in such a position that its convex dorsal surface shall cor- 

 respond to the concave line formed by the maternal sacrum and 

 coccyx. Hence the dorso-sacral position is the normal one, be- 

 cause it is that which is most favorable to the prompt and easy 

 passage of the fetus through the birth-canal with safet}* alike to 

 the fetus and mother. 



In those positions where the curvature of the fetal body does 

 not correspond to that of the birth-canal, the extremities of the 

 fetus tend to push against the sides or walls of the canal and be- 

 come impacted therein, injuring more or less seriously the soft 

 parts of the mother or blocking the progress of the fetus. It is 

 also to be considered that when the dorsum of the fetus cor- 

 responds to the sacrum of the mother the actual transverse diam- 

 eters of the fetal body a.ssume the most favorable relations to the 

 various diameters of the pelvis of the mother. 



In the smaller domestic animals, the limbs of the fetus are not 

 so long comparatively, nor so rigid ; the neck of the fetus is 

 usually much shorter. The body is less curved and more pliable, 

 so that it may be more readily bent dorsalwards than in the 

 larger animals. The head, in some of the smaller animals, such 

 as the carnivora, is large and offers alone as great an obstruction 

 as the head and forefeet together in the larger animals. There- 

 fore, in smaller animals, the anterior feet and legs usually pro- 

 ject backward beneath the fetal body and the head advances 

 alone. Because of the more direct and cylindrical form of the 



