302 NATURAL EUTOCIA. 



slides on a surface that is plane and even convex, but not at all 

 concave. Although in the first variety every thing is disposed in 

 the most advantageous manner, the presence on the one hand of 

 the rectum, and on the other of the bladder and sacro-vertebral 

 angle, cannot after all, render the second and third any more diffi- 

 cult or dangerous. 



2. Occipito-Posterior Position. 

 320 in 35,895 cases, Madame Lachapelle; 203 in 20,517, Madame Boivin. 



741. Of far less frequent occurrence than the occipito -anterior 

 position, the occipito-sacral position is also much less easy, and less 

 natural. In order to emerge first, the occiput is compelled to tra- 

 verse the whole extent of the anterior face of the sacrum, the coccyx 

 and perineum, that is to say, a surface of from seven to eight inches 

 in length; while in the other position it escapes after passing over not 

 more than two inches. The posterior wall of the pelvis is deeply 

 excavated, while its anterior half circle is rather convex than con- 

 cave; the summit of the head falls nearly at right angles upon each 

 point of that wall, and the occiput meets a new resistance at every 

 effort; which is not the case when it is turned in front. The vertex 

 cannot present itself at the vulva until a considerable part of the 

 breast has descended into the excavation; so that it is no longer 

 merely the occipito-bregraatic diameter, but it is a line drawn from 

 the anterior fontanel to the posterior part of the thorax that is re- 

 ferred to the antero-posterior diameter of the lower part of the ex- 

 cavation. Here the vertebral column is so strongly curved that it 

 cannot but lose a considerable part of the force impressed upon it 

 by the womb, before that power can reach the head. The head 

 and trunk both together, and not the head alone, traverse the exca- 

 vation and inferior strait; and finally, the forehead is commonly too 

 broad to fill up the top of the pubic arch accurately, and the coccy- 

 pubic diameter may on this account lose as much as half an inch of 

 its length. 



742. The causes that occasion the posterior position to occur are 

 little understood; it is better frankly to avow our ignorance than 

 vaguely to refer them to this or that shape of the pelvis, to the direc- 

 tion, or disproportioned dimensions of the womb, to certain habits 

 of the woman, to uncommon movements of the foetus, &c. The 

 only thing that can be affirmed about them is, that it is pretty com- 

 mon to meet with them several times in succession in the same 

 woman. Besides, this is a question that requires some careful re- 

 searches before it can be decided. Although the three principal 



