PELVIS. 



195 



rectly forwards, without any lateral deviation 

 inwards or outwards. In the Hunterian 

 Museum also, there is a rickety skeleton of 

 a child of six years, in which the pelvis 

 presents the angular deformity and approxi- 

 mation of the acetabula. In none of these 

 specimens is there any great backward curva- 

 ture of the spinal column, though, in the last 

 instance, the sacrum is bent so much forward, 

 that the tip of the coccyx is almost on a 

 level with the superior plane in the centre of 

 the opening. 



It is, however, especially remarkable that in 

 all these last-mentioned specimens, as well as 

 in that figured by Naegele and just described, 

 the angle of the bend or culm of the lateral 

 curve produced by the pressure inwards of 

 the heads of the femurs, takes place in the 

 acetabula at the line of junction of the two 

 upper pieces of the inuominatum, and not in 

 the superior branch_of the pubis itself, as in 

 most of the cases resulting from mollifies 

 ossium. This is evidently produced by the 

 more facile and greater yielding of the as yet 

 unossified cotyloid cartilage, rendered softer 

 and more tardy in ossifying, by the effect of 

 the disease upon its nutrition. 



That such a yielding does take place in this 

 cartilage from disease and pressure is shown 

 still more strikingly in another case in the 

 Hunterian Museum (No. 3423.), in which it 

 has bent outwards, instead of inwards, and 

 thus is produced an elliptical distortion of the 

 pelvis. This skeleton is from a young subject, 

 in which the pelvic bones had not yet become 

 soldered together. The head and neck of the 

 left femur are nearly destroyed by caries, which 

 doubtless also extends to the acetabulum 

 itself. Both the femurs are extremely flexed 

 and adducted on the pelvis, and seem, espe- 

 cially on the diseased side, to have, by the 

 constancy of this position, pushed upwards 

 and backwards the pubis, so as to cause a 

 distinct bend at the cartilaginous cotyloid line 

 of junction, and an elevation of the pubic 

 symphysis. By this means, the acetabula are 

 pushed outwards, and the superior pelvic 

 opening assumes an elliptical shape; though 

 the cotylo-sacral arch is but slightly spread 

 out, and the ischial tuberosities are normally 

 placed. The lumbar curve and sacral pro- 

 monotory deviate slightly towards the left 

 side, and the bones are remarkably small and 

 light, showing the prevalence of the rickety 

 tendency. 



From these cases, it seems reasonable to 

 draw the conclusion, that the softened infant 

 pelvis does in a great many cases assume the 

 cordiform shape, and that without any back- 

 ivard spinal curvature ; but, on the contrary, 

 the case quoted by Naegele shows that it is 

 co-existent with excessive forward curvature 

 of the lumbar spine, such as would throw the 

 weight of the body entirely in front of the 

 vertically placed pelvic brim ; and thus, accord- 

 ing to Dr. Murphy's view, of necessity, pro- 

 duce the ovate and not the angular deformity. 



We may also conclude that when, by mecha- 

 nical causes, the angular shape is impressed upon 



the softened infant pelvis, it will yield most 

 readily and extensively at its weakest point 

 viz. the still cartilaginous line of ilio-pubic 

 junction in the acetabulum ; and that, as in the 

 instances now given, and indeed in all that I 

 have myself examined, the shape of the angu- 

 lar pelvis resulting from rickets in infancy is 

 never rostrated, in the sense to which that 

 expression is confined in the present article ; 

 but, that this form is usually seen only in 

 the angularly deformed pelvis resulting from 

 the mollities ossium of adults, and commenc- 

 ing after the pelvis has attained its adult de- 

 velopment and consolidation, when the bend 

 most commonly takes place in the centre of 

 the superior pubic ramus, which, in thick- 

 ness, and, in some diseased conditions, as the 

 analysis before given shows, in composition 

 also, is the weakest point of the pelvic circle 

 in the adult. This will, I think, be found a 

 general and useful distinguishing mark between 

 the angular pelvis resulting from rickets, and 

 that of the adult mollifies ossium. 



Whether, on the other hand, the adult pel- 

 vis, softened by mollities ossium, or the rickets 

 of adults, ever assumes the ovate form of dis- 

 tortion, is a question of supposition merely. 

 I have not been able to find any recorded 

 cases of such a result, though there is no evi- 

 dent reason why this should not occur, under 

 certain mechanical conditions. Rokitansky 

 found that the ovate and hour-glass distortions 

 are, almost without exception, the result of in- 

 fantile rickets. 



MECHANISM OF THE PRECEDING PEL- 

 VIC DISTORTIONS. In considering the forces 

 which operate in producing the two principal 

 varieties of pelvic distortion previously treated 

 of, it is necessary carefully to separate those 

 resulting from mechanical position, from 

 those which arise from muscular action alone. 

 In considering the former, it will be necessary 

 as carefully to separate the idea of the line of 

 gravity i. e. a perpendicular line let fall from 

 the centre of gravity from that of the line 

 of pressure, which must necessarily pass 

 through the osseous supporting structures, 

 whatever disposition they may have. 



The centre of gravity of the trunk itself is 

 that which influences most considerably the 

 form of the softened pelvis in the sitting as 

 well as the upright position. This is placed 

 by Weber in the transverse vertical plane of 

 the spinal column, which here falls consi- 

 derably in front of the vertebrae, in the tho- 

 racic cavity, at the level of the sterno-xiphoid 

 articulation (see^/Jg. 122. A, a). 



In the most easy standing position, this 

 centre of gravity is placed directly above that 

 of the whole body, at the sacro-lumbar articu- 

 lation (A, c) ; so that perpendicular lines let 

 fall from each to the ground will exactly co- 

 incide, and (in the well-made subject, after 

 passing through the sacral promontory and 

 the acetabula) fall between the feet as the 

 basis of support. In the sitting posture, it 

 falls a little posterior, between the ischial tu- 

 berosities. 



To preserve the standing posture, it is 



o 2 



