PELVIS. 



183 



of the great glutei muscles upon softened 

 ischia. In some instances, however, this length 

 and projection of the spines cannot be thus 

 accounted for. Obstruction may occur before 

 the head reaches the tuberosities in these cases. 

 Their relative positions may be altered also by 

 fracture. 



Pelves in which the cavities are contracted 

 at the lower part by disease, present the chief 

 obstacles at the interior outlet, and will be 

 considered under that head. 



A variety of the shape of the pelvic cavity 

 is mentioned by Murphy, as forming a contrast 

 to the funnel-shaped masculine pelvis. It is 

 the funnel-shaped reversed by the gradual wi- 

 dening of the transverse diameters downward ; 

 but, being generally attended by some contrac- 

 tion at the brim, it belongs rather to the classes 

 of deformities before described, and would 

 seem to resemble the first case of Ramsbo- 

 tham's there cited, and to be the beginning of 

 a more complete ovate deformity, afterwards 

 to be mentioned, as shown by the widening of 

 the inferior opening. 



Distortions affecting the outlet only or prin- 

 cipally. In these cases the greatest obstruc- 

 tion occurs at the inferior outlet, which, being 

 comparatively independent of the brim and 

 cavity, may be contracted without any im- 

 portant alteration in their shape or size. 



Contraction of the transverse diameter is 

 the most frequently seen. The ischial tube- 

 rosities are approximated, and the space of 

 the sub-pubic arch lessened ; and thus, indi- 

 rectly, the antero-posterior diameter is ren- 

 dered less effectual. Cases are frequently 

 presented to the obstetrician, and many are 

 on record, in which obstruction has occurred 

 at the sciatic tuberosities, and the use of the 

 forceps been rendered necessary. The normal 

 distance between the centres of these processes 

 is from 4 inches to 4^. In my measurements 

 I have met with as small a distance as 3f 

 inches in female pelves, in which the trans- 

 verse diameters were generally rather small. 



The bi-parietal diameter of the fcetal head 

 is said to be 3^ inches, and is placed obliquely 

 between these tuberosities, as the occiput 

 emerges under the sub-pubic arch. The 

 soft parts, besides, will occupy at least thiee- 

 fourths of an inch. Thus wiih a large 

 and well-ossified head and contracted inter- 

 tuberal distance, the impediment is great. 

 The diminished span of the sub-pubic arch, 

 also, pushes back the head upon the coccyx, 

 and renders a greater enlargement than usual 

 of the antero-posterior diameter necessary ; 

 while at the same time the great sacro-sciatic 

 ligaments are also approximated and rendered 

 extremely tense, and thus the oblique di- 

 ameter between them and the ischio-pubic 

 rami is also considerably diminished. 



The special cause of this deformity, when not 

 dependent upon the infantile, masculine, or 

 funnel-shaped pelvis before described, is to 

 be attributed to the action of the great glutei 

 muscles, in standing and walking, pressing 

 upon the ischia partially softened by disease. 



Contraction of the antero-posterior diameter. 



This results in most cases from anl-ylosis 

 of the sacro-coccygeal joint. The coccyx is 

 rendered immoveableand incapable of yielding 

 to the head of the fetus, so as to bring about the 

 usual increase in the antero-posterior diameter. 

 In addition, it is usually ankylosed in an 

 almost horizontal direction, with its apex 

 directed forwards and its surfaces upwards 

 and downwards, a position which is brought 

 about by the resiliency of the sacro-sciatic liga- 

 ments and ischio-coccygeus muscles, and by a 

 continued sitting posture ; and thus the an- 

 tero-posterior diameter is still more diminished. 



The foetal head is arrested by, and rests on, 

 the coccyx, and the obstruction is only over- 

 come by the giving way of the bone at or 

 near the ankylosed part. The delivery gener- 

 ally requires instrumental aid. 



Examples of this condition are nume- 

 rous. In the practice of Dr. Michaelis of Kiel, 

 a fracture of the parietal bone of the infant 

 was occasioned by an immobility of the coccyx 

 resulting from ankylosis.* Dr. Merriman, in 

 a Letter to Dr. Lee, published in the Med. 

 Gazette (1843, p. 224.), mentions a casein 

 which the point of the coccyx snapped off in 

 three successive labours, and he had observed 

 one or two other cases in which this occurred, 

 and no ill consequences followed. In one, 

 the coccyx was turned upwards, and there 

 was a considerable bulk of ankylosis, pro- 

 duced by a fall. Dr. F. Ramsbotham also 

 mentions three instances in which fracture 

 at or near an ankylosis of the coccyx took 

 place. Dr. Lee relates also a case which 

 occurred in the practice of a country surgeon, 

 in which the lower end of the sacrum curved 

 much forward and was ankylosed to the upper 

 coccygeal bones, the last only being moveable. 



In* certain cases the contraction of this 

 diameter is brought about by the tilling forward 

 of the lower end of the sacrum, with an almost 

 horizontal direction of the lower part of the 

 sacral curve. I have met with two or three 

 pelves in which this condition is present, 

 coexistent with, and evidently caused by, a 

 curvature of the lower dorsal region of the 

 spinal column backwards. By such a curvature, 

 the line of gravity of the trunk is displaced back- 

 wards, passing through the sacrum consider- 

 ably behind its base, and making traction upon 

 it in that direction. The promontory of the 

 sacrum is by this means dragged backwards 

 and upwards, and the conjugate diameter of 

 the brim increased, so as to be equal to, or 

 greater than, the transverse. The shape of 

 the brim is thus rendered oblong or oval in 

 the opposite direction to, and contrasting 

 with, the ovate deformity presently to be 

 described. The axis of the superior plane is 

 rendered more horizontal than normal, by the 

 increase of the pelvi-vertebral angle, thecotylo- 

 sacral arch more open in its curve, and the 

 acetabula in some measure approximated. The 

 cavity of the pelvis is narrowed antero-pos- 

 teriorly by the gradual advance downwards 

 of the posterior wall, and the vertical curvature 



* Neue Zeitschrift fur Geburtskunde, t. iv. 1836. 

 N 4 



