PRESENTATION OF THE VERTIX. 299 



On this subject I think I ought to point out a contradiction found 

 in the authors on midwifery. On the one hand, they say that the 

 right-acetabular position is determined by the presence of the rec- 

 tum on the right side of the sacrum, and on the other, that this same 

 position is rendered less favorable by the friction of the head on the 

 bowel on the left. 



Remarks. The act of rotation in these two positions has not been 

 interpreted in the same way by all authors. Madame Boivin and 

 some others account for it by referring it to the contraction of the 

 muscles that line the excavation. But it is evident that such an ex- 

 planation is inadmissible; for, 1. This rotation sometimes takes place 

 when the head is still above, and most generally does not occur 

 until it is below the muscular bundles, to whose contractions it is 

 attributed; 2. If the pyramidal and internal obturator muscles, by 

 their contractions, could make the head revolve on its own axis, they 

 would carry it across the pelvis, and not from front to rear. By 

 referring it to the action of the sterno-mastoid muscles of the foetus 

 itself, an opinion has been advanced still less worthy of being com- 

 bated than the preceding one. 



Besides, what need is there for us to look for the cause of this 

 movement, either to the muscles of the pelvis, or of the child's neck? 

 The occiput turns towards the pubis, because it finds a vacant space 

 there, while it is strongly resisted on the sides; it deviates from its 

 original direction for the same reason that the forehead turns, at the 

 superior strait, towards the sacro-vertebral angle. The form of the 

 pelvis and the laws of mechanics give a perfectly clear account ef 

 this peculiarity: the anterior wall of the excavation, which is much 

 shorter than the posterior, being deeply notched and somewhat 

 hollowed out, any salient part of the head, when strongly urged by 

 the contractions of the womb, could scarcely fail to engage in it, not 

 only without the assistance of the contractions of the inclined planes, 

 but even in spite of those contractions, were they really to take 

 place. 



C. Third Variety. 



Occipito-pubic position. 



The 3d of Solayres, Baudelocque, &c.: 6 in 20, 517, Madame Boivin. 



737. The ancients regarded the occipito-pubic as the most fre- 

 quent position, because they did not distinguish the two antero- 

 lateral ones, and only judged from what is observed at the inferior 

 strait. Baudelocque admitted it rather for the purpose of filling 

 up his plan than from the testimony of his senses. Since his time 



