MKCIIAXISM OF I'AUTilUTKiX. 2h',\ 



j^reater than its width this rotation is effected spontaneously at the 

 commencement of birtli. So that these oblique positions are as favour- 

 able as the dorso-sacral position. 



3. Mechanism of Parturition in the Domo-Uial Positions. — These 

 lateral positions — also two in number and symmetrical — are, accord- 

 inf^ to Saint-Cyr, rarely primary, but, as Kainard remarks, are some- 

 times found as sccondar;/ j>ositions, due to the reduction of some 

 mal-presentations. The latter authority asserts that spontaneous birth 

 is impossible in these positions, because the chest of the fa;tu8 

 presents its greatest diameter to the smallest diameter of the pelvis 

 of the mother. This, however, is an exaggeration, as the bis-iliac 

 diameter is sometimes equal, or even superior, to the sacro-pubic 

 diameter; so that it is not always absolutely impossible for delivery to 

 occur spontaneously in these positions ; though it is very true that it 

 is alicays more dillicult, and sometimes impossible, if the position is not 

 altered. Independently of the disproportion between the diameters of 

 the pelvis and the corresponding diameters of the fa-tus, here also we 

 find the two salient parts of the latter — the sternum and dorsal spines 

 jamming against the tw^o resisting parts of tlie ])elvic circumference — 

 the ascending branch of each ilium, and it will he readily seen that in 

 some cases tliese will prove an insurmountable obstacle. Nevertheless, 

 as a general rule, this obstacle may be easily turned, if the pelvis is 

 sutliciently wide, by merely causing the body of the fcetus to rotate in 

 such a manner that its greatest diameter will be brought opposite the 

 oblique diameter of the inlet, which extends from the ilio-pectineal 

 ridge to the sacro-iliac articulation on the opposite side. Then its 

 <;ntrance into the pelvic cavity, and complete expulsion, is rendered 

 possible. 



But if the pelvis is narrow, the faulty position must be modified at 

 the commencement of birth so as to make it oblique or dorso-sacral, 

 and if the ftetus is not large the croup will probably follow without 

 (lifliculty. If, however, the fa-tus is large, it should be placed in the 

 <lorso-ilial position in order to accommodate it to the larger diameter 

 of the pelvis. 



It will be seen that the dorso-ilial positions may sometimes admit of 

 spontaneous birth, but that it will also happen that aid will be neces- 

 sary to effect delivery. 



Posterior Presentation. 



Mechanism of Parturition in the Lumbosacral Position. — Of the 

 positions in which we may have a breech or posterior presentation, 

 only one is compatible with spontaneous delivery— the lumho-sacral ; 

 though even this is denied by other authorities. Tiie fu'tus is pre- 

 sented by the breech, the loins towards the sacrum of the mother, 

 the hind limbs in complete extension and entering the inlet, so as 

 to open the passage for the body ; and though this position may 

 appear to be favourable for the expulsion of the young creature, 

 yet it is far less so than the first anterior position. The croup of 

 the fcetus is a rounded voluminous mass which does not admit of 

 much compression, and the diameters of which - particularly the trans- 

 verse—are nearly equal to those of the pelvis; it is, therefore, not 

 well disposed for passing through the latter, and, in addition, its upper 

 part presses against the sacro-vertebral angle ; while the stifles, which 

 are salient, press against the edge of the pubis, and the hip-joints 



