GENERAL APPEARANCE OF THE ARTICU LATED PELVIS.—When the bones of the pelvis are articulated together, its whole ap pearance is that of a section of a cylinder or bent tube, having an anterior, posterior, and two lateral, and a superior and inferior aspects.
Its anterior aspect ( fig. 80.) is bounded on each side by a line passing from the anterior superior iliac spine, along the anterior border of the cotyloid cavity to the ischiadic tube rosity on each side. It presents the pubic symphysis directed downwards and forwards in the median line, and the obturator fora mina directed forwards, outwards, and down wards on each side. As first noticed by Cuvier, this oblique direction of the sym physis pubis is peculiar to the human species, that of animals being parallel with the axis of the body. In addition to these parts, already described, are two large notches formed by the approximation of the inno minate bones. Of these the superior one, which may be called the ventral notch, is formed by the vertical and horizontal portions of the anterior border of the innominate bones on each side with the peculiarities before men tioned in its description. In the natural posi tion of the pelvis this notch exposes to the view most of.the internal surfaces of the pelvis to be described from the superior aspect. The inferior notch is formed by the oblique ascent towards the symphysis pubis of the branches of the ischium and pubis, forming what is termed the sub-pubic arch. Its apex is limited by the arched sub-pubic ligament, and there, in the male, it is generally about an inch wide, and at the base, between the ischiadic tuberosities, about three inches wide. The edges of this arch are in both sexes projected forwards, more or less, so as to present an in clined surface to the plane of the arch. This eversion as well as the measuretnents are, however, considerably greater in the female pelvis, hereafter to be considered.
The lateral aspeets of the pelvis present the anterior half of the external surface of the ilia above ; the cotyloid cavities directed outwards, -forward and downwards, in the middle ; and the descending branch and hinder part of the tuberosity of the ischia below, the latter being directed outwards and backwards.
The posterior aspect presents the posterior surface of the sacrum and coccyx in the cen tre, the most prominent point, in the erect position of the body, being the divided spine of the fourth sacral vertebra. On each side, next in succession, occur the overhanging and projecting tuberosities of the ilia, constituting two prominences next in importance, conceal ing the sacro-iliac articulations, and caus ing the lateral parts of the three upper sacral bones to appear as a deep groove on each side for the reception and origin of the powerful erector muscles of the back. Be tween these points also the last lumbar ver tebra appears sunk between the two iliac crests, so that its upper surface is on a level with their most elevated central portion. Below the sacrum, the coccyx projects downwards and forwards in a salient median point, which separates and completes the inner boundary of the sciatic notches on each side, converted into foramina by the greater and lesser sacro sciatic ligaments. The distance of the edges of' the sacrum and coccyx from the spines and tuberosities of the ischia, and consequently the size of the openings, is less in the male than in the female ; but the depth of the notches vertically is greater in the former. Above these are seen the posterior half of the external iliac surface, or external iliac fossa, surmounted by the rising crest.
The superior aspect (fig. 80.)reveals to view the whole of the internal surface of the pelvis, which presents two well contrasted portions, divided by a rounded edge or border, of which the superior is wide, expanded, and deficient in front, and is called the large, or false pelvis ; and the inferior, narrower, more complete, and more compact, is called the small, or true pelvis ; while the border which separates them is commonly expressed II8 the brim, or su perior outlet of the true pelvis.