_Distinction between the male and female pelvis._ At the brim, the female pelvis presents several well-marked points of distinction from that of the male. The male pelvis has a contracted brim of a rounded or rather triangular form, with the promontory of the sacrum considerably projecting; whereas, that of the female is spacious, of an oval shape, and with a slightly prominent sacrum, thus affording more room for the passage of the child through the brim. The cavity of the male pelvis is deep, while in the female pelvis it is shallow, a circumstance which is very strikingly seen in comparing the length of the symphysis pubis in each, that of the male pelvis being nearly double the length of the female. This is an important point of difference as regards parturition, because in a shallow pelvis, the extent of surface exposed to the pressure of the head will be much less than where it is deep, and hence the resistance to the passage of the child will be proportionably diminished: in confirmation of this, we find that tall women, in whom the pelvis is usually deep, do not, on the whole, bear children so easily as women of middling stature in whom the pelvis is more shallow. The capacious hollow of the sacrum in the female pelvis adds also greatly to the extent of its cavity, and peculiarly adapts it for parturition, the injurious pressure of the head upon the soft linings of the pelvis being thus prevented, and every facility afforded for its quick and easy transit through the cavity. This applies especially to the neck of the bladder, which would almost inevitably suffer in every labour, were it not for the ample hollow of the sacrum relieving the pressure of the head against the anterior portions of the pelvis. The bones of the female pelvis being more slender and delicately formed, the foramina ovalia and sacro-ischiatic notches are wider, and thus add still farther to the capacity of the cavity. In no part of the pelvis is the difference between the sexes more strongly marked than at the outlet. The spacious and well-rounded arch of the pubes in the female of the slender rami, is a striking contrast to the contracted angular arch of the male pelvis; and the tuberosities of the ischium being much wider apart, the head is enabled to pass under the arch with greater facility, and thus still farther to relieve the anterior of the pelvis from its pressure. The length of the sacro-sciatic ligaments, and the mobility of the coccyx upon the sacrum, by which it can be forced backwards to the extent of an inch by the pressure of the head during labour, not merely serve to distinguish it from the male pelvis, but afford a beautiful instance of design and adaptation.