S26 UNNATURAL EUTOCIA. 



bis-iliac diameter, more frequently in that of one of the oblique ones, 

 or at least, after being slightly inclined, one forwards and the other 

 backwards, provided they were previously quite transverse. When 

 in the excavation, they are observed to engage in the perineal strait; 

 sometimes parallel with the bis-sciatic line, at others by following 

 the oblique diameter, and most frequently, after one of them has 

 been placed behind the symphysis pubis, and the other in front of 

 the sacrum. 



784. The arms and shoulders present themselves in their turn, 

 and act like the hips, with the exception only, that they more rarely 

 fail to execute the pivot motion before they pass through the vulva, 

 even though they had previously affected a transverse position; 

 being repelled by the anterior edge of the perineum, these different 

 parts, as they emerge, are raised upwards towards the mons veneris; 

 to accommodate itself to the curve of the pelvis and genital parts, 

 the foetus bends in the shape of a very long arc of a circle, convex 

 behind and concave before, as it does in an anterior position. The 

 elbow that is below the pubis shows itself first at the upper part of 

 the vulva; but the opposite arm and shoulder, more particularly 

 urged by the efforts of the womb, proceed from behind forwards 

 along the posterior median line, and actually are the first to escape 

 from the pelvis; the edge of the perineum immediately afterwards 

 retires upon the neck, as if to permit the trunk to fall back towards 

 the anus, and the other shoulder to disengage from beneath the pubic 

 symphysis ; the back then turns back again, as by a sort of move- 

 ment of restitution, M'hich replaces the shoulders, the one to the left 

 and the other to the right, or diagonally. The head cannot become 

 engaged without being strongly flexed; on the one hand the occiput 

 almost invariably deviates towards one of the sacro-iliac symphyses; 

 on the other, the occipito-frontal diameter, or even the entire head, 

 represents a lever of the first kind, whose anterior extremity more 

 particularly supports the action of the expulsive powers; the chin, 

 although more or less prevented by the breast, ends however by be- 

 ing depressed, and the occipito-mental diameter by finding itself al- 

 most parallel with the axis of the strait; the forehead and anterior 

 fontanel come, one after the other, to hide behmd the symphysis of 

 the pubis, and thenceforth the occipito-bregmatic circumference is in 

 correspondence with the plane of the pelvic margin, as in all the an- 

 terior positions. 



785. When in the excavation, the head rolls on the inclined planes, 

 replaces itself in an antero-posterior direction by means of the pivot 

 motion, and afterwards glides with much more diflUculty than when 

 the occiput is forwards; the breast, which is situated in front, opposes 



