504 



CYCLOPEDLV OF LIVE STOCK AND COMPLETE STOCK DOCTOR, 



foetus, here also we find the two salient parts of the latter — the sternum and 

 dorsal spines — jamming against the two resisting parts of the pelvic cir- 

 cumference — the ascending branch of each ilium — and it will be readily 

 seen that in some cases these will prove an insurmountable obstacle. Nev- 

 ertheless, a? a genera] rule, this obstacle may be easily turned by merely 

 causing the body of the fa-tus to rotate on its axis in such a manner that 

 its greatest diameter will be brought opposite the oblique diameter of the 

 inlet, which extends from the ileo-pectineal ridge to the sacro-iliac articula- 

 tion on the opposite side. Then its entrance into the pelvic cavity, and 

 complete expulsion, is rendered possible. 



XIX. Mechanism of Parturition in the Posterior Lumbo-Sacral Position. 



Of the four positions in Avhich we may have a breech or posterior presen- 

 tation, only one is compatible with spontaneous delivery — the lumbosacral. 

 The foetus is presented 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 favorable for the expulsion of the young creature, yet it is far less so 

 than the first anterior position. The croup of the foetus is a rounded 

 voluminous mass which does not admit of much compression, and the 

 diameters of which — particularly the transverse — 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 against the branches of the ilium. Entrance into 

 the inlet must therefore be slow, difficult and painful for the mother, and 

 when this first obstacle is overcome and the croup is in the pelvic cavity, 

 the chest has to follow, and to submit to the same compression at the inlet 

 as in the anterior presentation. But this part of the foetus is much less 

 favorably disposed for such a reduction of dimensions in this position, as 

 the resistance oft'ered by the walls of the maternal pelvis has a tendency to 

 erect the dorsal spines and to carry the ribs and sternum forward — all this 

 going to increase the diameter o-f the foetus in every direction. It is only, 

 then, by direct compression or crushing, that the necessary diminution in 

 the diameters of the young creature can be efiPected, and not by a kind of 

 physiological decrease, as in the anterior presentation. 



There is also the obstacle offered by the hair of the foetus, the "set" of 

 which is against the direction of movement ; and this obstacle will be greatly 

 increased if the fluids have escaped for some time, and the parts are more 

 or less dry. 



Taking all these considerations into account, it will be seen that in this 

 position, even when birth is possible with extraneous assistance, labor must 

 be long and exhausting, and that the young creature incurs the greatest 

 danger. Labor, however, is more likely to be successful and less tedious if 



