But the development in size may proceed to its fullest extent, and yet the development in shape and proportion be arrested, and the transitional form unchanged. In a spe cimen given by Dr. Murphy, of a female adult pelvis, the diameters were above the standard size, but the antero-posterior dia meter was .5i inches, and longer than the transverse ; the transverse of the outlet pro portionately diminished ; the cavity shallow ; and the general form of' the pelvis infantile ; but the bones perfectly ossified. The pelt is has the shape and proportions of that of a child, and the size of an adult female (see fig. 113.). To judge from the appearance of this specimen, as seen in the drawing given by Dr. Murphy, it seems to be a pelvis in which the transverse processes of the last lumbar vertebra are enlarged, ankylosed to the sacrum, and ar ticulated with the ilia, giving the appearance of five sacral holes instead of four. This would account for the increased antero-posterior diameter, and apparent -elevation of the sacrum. Cases of this kind are more especially de scribed in the latter part of this article.
Dr. Knox has observed that the male pelvis also sometimes permanently retains the infan tile form, to which it is normally more ap proximated than the female. In one of this kind in his possession, the greatest transverse diameter was nearest the sacrum, and only iths of an inch larger than the conjugate.
Masculine pelvis. —ln females of a robust frame and powerful developntent of muscle, and accustomed to hard masculine labour, the pelvis often presents the character of the male in many important respects. The transverse measurement of the brim is proportionately smaller, the antero-postermr diameter being often increased, and the shape of the brim is thus rendered more oblong ; the sacrum is narrower, the pubic sy-mphysis longer, and the cavity deeper, and rendered funnel-shaped and less roomy, by the approxitnation of the ischial tuberosities ; by which also the sub-pubic angle is diminished to 60° or 70°. The ischial spines are longer, stronger, and project more inwards; the ilia are less expanded, and the bones larger, more massy, and more marked than in the "standard" pelvis.
Dr. Knox is of opinion that in many in stances the true pelvis may be of normal size, and yet the haunches be remarkably narrow, owing to a want of proportion of the true and false pelvis ; so that while the walls of the latter are flat, upright, and approximated, the true pelvis is of proper dimensions. He adds, moreover, that the opposite dispropor tion sometimts is present, and may mislead the obstetrician by giving an apparent breadth of haunch, while the contraction of the true pelvis may be considerable. He considers it
to result from the entirely different and inde pendent development of the false and true pelvis.* I have met with many specimens of .the masculine form of pelvis in the dissecting rooms, from among the laborious women of this metropolis. In Dr. Murphy's experience it is more common than had been hitherto supposed.
The obstruction in this form of pelvis is met with chiefly in the deep funnel-shaped cavity, at the"projecting ischial spines, or at the infe rior outlet, under the narrow arch, and be tween the tuberosities, and is rendered the more serious by the fcetal head in these cases being generally more ossified than usual. The great inward projection of the sciatic spines somethnes affords an obstacle to the passage of the head. The average normal distance between them will be found, on refer ence to the tables, to be 4 inches. During the turning of the head in the most frequent positions, the inter-temporal and inter-zygo matic diameters of the fcetal head, the former of which is placed by Dr. Murphy at 3 inches, and the latter at 31 to 4 inches, are placed obliquely between them. In one or two in stances I have found the sciatic spines as near to each other as 3+ inches, and in one it was not co-existent with any extraordinary massy or masculine proportions, but simply with small transverse diameters. In the fronto cotyloid and fronto-pubic positions, or with a large fcetal head, the approximation of the sciatic spines becomes a serious impediment to labour. In this pelvis the sacro-coccygeal articulation is said by Dr. Murphy to be ge nerally' less moveable, and the sacro-iliac joints unyielding, and that a bony ridge is often found on the posterior surface of the narrow pubic symphysis.
The cause of this form of pelvis seems to be, an advanced condition of ossification in a pelvis which would otherwise have been "infantile," brought about by the development of unusual muscularity, corresponding to the laborious employment of the individual. This action of the pelvic muscles will have also the effect of impressing irregularities upon the bones into which they are implanted, or over which they act. The tension of the posterior spinal and abdominal muscles against those of the leg would tend to elongate the pelvis, while the powerful great glutei, much used in supporting or raising heavy weights, will press inwards the ischial tuberosities, and narrow the sub pubic arch.