PELVIS. 



14-7 



turition, in being compensatory for the great 

 curve of the pelvic axis, and the change of 

 direction forward of the inferior from the 

 superior outlet. This curve is dependent upon, 

 and follows the curve of, the sacro-coccygeal 

 column, which, being more acute and di- 

 rected more forwards below, affords the chief 

 support in the earlier months of pregnancy to 

 the uterus and its contents, which lie in the 

 axis of the superior outlet, which axis, as we 

 have seen, impinges below upon the coccygeal 

 bone. Now, the coccyx, being principally 

 held up in its forward position by the elastic 

 sciatic ligaments and by the resilient ischio- 

 coccygeus and levator ani muscles, affords a 

 resisting support which is at once powerful 

 and yielding, and acts like an elastic spring in 

 supporting the uterus and its delicate contents 

 under the effects of accidental shock. The 

 female coccyx is much more mobile at every 

 age than the male, and when ankylosed to the 

 sacrum it is less favourable both to pregnancy 

 and Jabour. In the more advanced stages of 

 pregnancy, however, the uterus rises into the 

 abdominal cavity, and rests mainly upon the 

 smooth concave surfaces of the pubes and the 

 soft muscular margins of the pelvic brim, 

 being embraced and supported above and in 

 front by the abdominal muscles. To allow 

 the great expansion of the uterine contents, 

 the broad ventral notch and expanding iliac 

 wings are dispositions of great significance. 



During labour, the fetal head enters the 

 brim of the pelvis in the oblique diameter, 

 which being less encroached on by the muscles 

 is the best adapted to receive it, as well as 

 by its correspondence in form to the brim 

 in that direction. Then traversing the pelvic 

 axis, it passes, first downwards and backwards, 

 and then, being turned forwards by the sacro- 

 coccygeal curve, escapes under the pubic arch 

 and through the inferior outlet. The fetal 

 occiput is directed generally in the left oblique 

 diameter, towards the left ilio-pubic junction 

 (in 69 per cent, of the cases Naegele to 

 80 per cent. Boivin), and in its progress is 

 twisted gradually forwards and towards the 

 median line by the impingement of the parietal 

 protuberance upon the inclined plane of the 

 pyriformis muscle and upon the projecting 

 ischial spine, until it emerges under the sym- 

 physis pubis, around which it turns vertically 

 as round a centre ; the real centre of its 

 motion, however, being, as we have before 

 seen, a little in front of and below the pnbis. 

 The more anterior part of the fetal head, 

 then, traversing the circumference of the sub- 

 pubic circle, extends the coccyx, and passes 

 between the tuber ischii, distending the sacro- 

 sciatic ligaments and perineum, and turning, 

 as it does so, on its own transverse axis. 



In a well-formed woman, according to 

 Naegele, the superior plane of the pelvis will 

 be horizontal when the trunk is between the 

 sitting and recumbent positions (i. c. when 

 it forms an angle of 30 with the horizon). 

 In such a position traction on the head of the 

 child should be perpendicular. 



In sustaining these evolutions, the pelvic 



circle necessarily is exposed to a force not 

 hitherto considered, viz. pressure from within. 

 In well-formed pelves this pressure will be 

 exerted equally on all parts of the circum- 

 ference, from the adaptation, before mentioned, 

 of the child's head to the form of the pelvis. 

 The strain, however, will be most evidently 

 exerted upon the ligaments of the pubic and 

 sacra-iliac symphyses. 



The question whether these ligaments yielded 

 during labour sufficiently to enlarge materi- 

 ally the diameters of the pelvis, is one which 

 has attracted the attention of anatomists and 

 obstetricians very much, particularly about 

 the latter end of last century, when M. Sigault 

 proposed, in lieu of the Caesarian section, the 

 section of the symphysis pubis, with a view of 

 affording greater pelvic diameters. 



Among the older writers on this subject 

 Mauriceau, Pen, Lamotte, Vesalius, Varan- 

 dens, Menard, and Voigt denied that separa- 

 tion of the pubic bones occurred during 

 labour. 



Some believed it to occur only in young 

 primiparous females ; others in primiparous 

 females of advanced age ; and others again 

 only in pelvic distortions or peculiar circum- 

 stances of pregnancy. 



Ambrose Pare, Pineus, Banhineus Riveanus, 

 Diemerbroek, Arniseus, Bianchi, Gregoire 

 Pineau, Duvernay, Bertin, Lev-ret, Santorini, 

 Spigelius, and Smellie, have observed this se- 

 paration in the dead parturient woman ; and 

 Guillemeau, Hildanus, Van Solingen, Ves- 

 lingius, Puzos, Soumain, Bikker, Arnault!, and 

 Morgagni in the living subject. Pare and Peu 

 asserted that they had seen cases where the 

 ilia had been separated from the sacrum ; and 

 Smellie relates a case where great pain at the 

 sacro-iliac joints rendered this probable. 



Of those who admit that relaxation of the 

 ligaments and consequent separation do take 

 place, Boivin, Louis, Severin, Pineau, and 

 Meckel consider it to depend upon softening, 

 thickening, and loosening of a single inter- 

 pubic fibro-cartilage, and deposition of fluid in 

 its meshes ; Meckel with Antoine Petit, deny- 

 ing the frequent existence of a separation be- 

 tween two plates of cartilage. ButTenon found, 

 that although, in most cases, the inter-pubic 

 fibro-cartilage was single in the male, in woman 

 it was generally double, and contained a slit 

 or cavity, with no connecting fibrous tissue 

 between the middle of the plates. And he 

 found this to be the case in the young as well 

 as the old, and before pregnancy as well as 

 after ; sometimes the slit was capillary, but in 

 one female, recently delivered, the cavity 

 would admit the forefinger. In none of his 

 examinations did he find any thickening, soften- 

 ing, or laxity of the fibro-cartilage itself, how- 

 ever recent the accouchment, although the 

 external investing ligaments of the joint were 

 relaxed and elongated. He considers, that if 

 in females where but one fibro-cartihiginous 

 plate is present, separation of the bones occurs 

 during labour, it must be by rupture of the 

 fibres of the disc or its separation from the 

 bone. It is, however, difficult to comprehend 



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