Dfferences of the pelvis in the sexes. —Of all the bones in the human skeleton, those of the pelvis offer the most distinct characters between the male and female sex.
In the fenzale (fig. 83.), the bones are lighter, shorter, and broader, less evidently marked by tuberosities and indentations re sulting from the attachments of the tendinous structures, and have in a less degree the peculiarities, before described, of the articu lations, as well as those resulting from their peculiar mechanism. The iliac crest is less arched, and presents less distinctly the S-like curve, the iliac wings are thinner and more expanded, and the internal iliac fossze larger, mare shallow, and directed more anteriorly, and the iliac ridge extending between the cotyloid and sacro-iliac joints is less massy, less suddenly arched, and longer. The ischia do not converge soinuch towards the inferior outlet, and with the tuberosities are less massy, wider apart, and shorter, and the spines are less marked, and directed less inwards, and the transverse diameter of the inferior strait is greater. The ascending branches and the descending branches of thc pubes are thinner, narrower, and more oblique, turn their inner borders more forwards, and at the same time afford a more rounded expansion to the pubic arch, at the expense of the obturator foramina, which are thereby rendered smaller and more triangular in the female. The symphysis of the pubis is not so deep, and the fibro-cartilage is wider, thicker, and more vertical in position ; the united angles are more flattened posteriorly, and the horizontal branch is longer, thinner, and directed inore transversely outwards, rendering the distance between the symphysis and the cotyloid cavity, and consequently the projection of the hips greater, and an increased transverse diameter of the brim.
The sacrum is wider and less arched trans versely, and its promontory does not so much overhang the pelvic cavity, and thus the su perior outlet has less of the heart shape, being in females more properly termed oval. This difference of shape is also contributed to by the less lateral obliquity of the superior branch of the pubes.
Whether the sacrum is less arched trans versely in the female, I endeavoured to ascertain by observations taken from eighteen subjects, of which half were male and half female. A strip of lead .1,th of an
inch thick was made to assume the form of the transverse curve of the sacrum, by being pressed across the anterior surface just below the promontory, and the breadth from one sacro-iliac joint to the other care fully marked off. From this, a line was drawn on paper, following the curvature re tained by the lead, the extremities of which line were joined by a straight line, forming a chord to the sacral arc. The distance of the centre of this chord from the centre of the sacral curve was then measured. In the nine males, the height of the arch thus obtained varied from six to nine lines ; in the nine females, five to nine lines,—the greatest num ber of the males being seven lines, and the greatest number of the females being six lines. In the single case of the female where the measurement was nine lines, the subject was old. When we consider, that in the great majority of instances the breadth of the sacrum measured along the curve was greater by 4 to an inch in the female, these results will yield a still greater relative depth to the transverse sacral curve of the male.
Besides this transverse arch, the vertical curvature of the sacrum is relatively much less in the female. This is more apparent in the direction of the three upper sacral pieces, which are generally little curved, and often almost plane in the female, while, in the male, the curve is most apparent in the centre and more uniformly distributed over the whole sacral surface. Upon this point, how ever, much difference of opinion prevails amongst anatomists ; Meckel and Ward agree ing with the opinion here enunciated, while Cloquet and Cruveilhier maintain that the curvature of the sacrum in the female is deeper and more regular. The experiments of Mr. Ward, however, correspond more entirely with my own observations on this point. Mr. Ward observes, in addition, that the male sacrum often approaches the form of' the female, but the female rarely to that of the male. In old women, however, I have often seen a great vertical curvature of the sacrum.