PELVIS. 



199 



f the pelvis, retain a sufficient degree of hard- 

 ness to resist the bending, then the inward 

 pressure of the heads of the femurs remains 

 in its full force, associated with the upward 

 and brickward pressure, and the deformity is 

 increased by the upright position (Jig. 122. c, 

 a b, a c). The same result is also produced 

 in an increased degree, if the leg bones yield 

 outwards, so as to direct the pressure of the 

 heads of the thigh bones more towards the 

 median line. This will be better understood by 

 referring to the diagram (Jig- 122. D, a b, a c). 



Naegele observes, that when the lower extre- 

 mities are curved and distorted the pelvis will 

 generally be deformed ; and that such a con- 

 dition more especially, or where one hip is 

 higher than the other, with an unsteady gait, 

 a projecting abdomen and lower jaw, and re- 

 traction of the arms and thorax, diminutive 

 stature, &c., should lead the accoucheur to 

 suspect deformed pelvis.* 



The adult pelvis, softened by malacos- 

 teon, appears to undergo greater distortion 

 than is proportionate to that of the leg 

 bones. In that upon which the experiments 

 before mentioned, to ascertain the proportions 

 of the osseous constituents, were performed, 

 the bones of the lower extremities were almost 

 entirely symmetrical and well formed, and the 

 proportion of earthy matter contained in the 

 femurs much greater than in the pelvic bones, 

 especially in the pubes (at one point of which 

 it was entirely deficient) and the sacrum. The 

 pubes, as they are also the thinnest pieces of 

 the innominate bones and sustain a great 

 amount of the inward pressure, which exists, 

 in these ases, to its full extent, seem to be 

 the first to give way in the more complete and 

 rapid softening of " mollities ossiian adultorum" 

 The consequence is, the approximation of the 

 acetabular extremities, and increased curve 

 of the cotylo-sacral arch, so as almost to touch 

 the sunken sacral key-stone ; and the starting 

 forward and upwards of the crown of the pu- 

 bic counter-arch, so as to produce the rostrated 

 symphysis. 



The muscles'before enumerated, which sup- 

 port the erect posture, as they are in the adult 

 more powerful and developed, have a corre- 

 sponding effect in increasing the contraction of 

 the diameters consequent on the distortion. 

 The bones yield between their contracting dis- 

 tances in the direction already impressed upon 

 them. The acetabula are pressed backward 

 by the psoae and iliacus muscles, and the 

 ischial tuberosities and trochanters approxi- 

 mated by the pressure of the great glutei, which, 

 aided by the pyrifonnes, will also draw for- 

 ward the lower part of the sacrum and coccyx. 

 The powerful influence of the adult muscles 

 upon the pelvic bones partially softened, and 

 especially that of the great glutei upon those 

 bounding the diameters of the inferior outlet, 

 will produce many of the pa tial deformities 

 before treated of, as the influence of mechan- 

 ical posture in a limited extent, or short dura- 

 tion of the softening disease, will produce 

 others, principally those of the pelvic brim. 

 * Lehrbuch, 444, 



The peculiar variety of the partial deformity 

 will depend upon the frequency of the use of 

 one particular posture or set of muscles ; and 

 this will depend chiefly, in the child, on the 

 concurrent ailments which usually affect it, 

 and in the adult on the nature of his or her 

 habits and employment. 



The degree of the backward curvature of 

 the cotylo-sacral arch seems to depend upon 

 the degree of anterior lumbar curvature, which 

 necessitates a forward projection of the femurs 

 to keep the line of gravity between the feet 

 (see/g. 122. E, a b). 



The rostrated pelvis, with elongated antero- 

 posterior diameters, apparently results from 

 the coincidence of the softened pubes with the 

 causes of oblong deformity before adverted 

 to, as produced by a backward spinal curve, 

 causing the line of gravity to fall considerably 

 behind the acetabula, and dragging backwards 

 the superior part of the sacrum. 



The mechanism of these important pelvic 

 deformities has been entered into more in 

 detail because of the evident practical infer- 

 ences which may be drawn from it with re- 

 gard to the treatment and position of children, 

 especially females, afflicted with rickety dis- 

 ease. 



Degree of obstruction. Pelves affected by 

 the foregoing distortions are usually arranged 

 by British obstetricians, according to the de- 

 gree of obstruction at the brim, into three 

 classes : 



1st. Those which will suffer the full-sized 

 foetal head to pass entire. 



2nd. Those through which delivery may be 

 accomplished "per vias naturales" by means 

 of premature labour, craniotoiny, or mutilation 

 of the foetus. 



3rd. Those in which the degree of defor- 

 mity is so extensive as to call for the Caesarian 

 section, or the very early induction of abor- 

 tion. 



The limits of the first class have been va- 

 riously stated by different obstetricians, accord- 

 ing to their opinions regarding the obviou 

 variations in size of the foetal head, and its de- 

 gree of ossification. The following list conveys 

 the opinions of the most eminent authorities 

 upon the lowest limits through which the foetal 

 head can pass entire : 



DIAMETERS 



Conjugate. Transverse. 

 Ramsbotham, Churchill Lee, and 7 . h . - 



most obstetricians - J ** 

 Aitken and Osborne - - 3 sufficient. 

 Jo-h. Clarke - - 3| 

 Burns, Davis, and Le R i - - 3? 

 Barlow (Essays) - - 2f 

 Busch (Berlin) - - - 2$ to 3 

 Ritgen 2 



The lowest limits of the second class of 

 pelves involves a great difference of opinion 

 as to the lowest space required for the safe 

 performance of craniotomy : 



O 4 



