126 



PELVIS. 



The inferior or sub-pubic ligament, (Hga~ 

 mentum arcuatum, f~) is the most powerful, 

 passing from one descending ramus of the 

 pubis to the other in an arched form. Its 

 place of attachment to the pubis is often 

 a well-marked surface, triangular, with the 

 base upward, and half an inch in depth, cor- 

 responding in this respect to the outline of the 

 section of this ligament. This ligament and 

 the anterior are the most intimately con- 

 nected with the fibro-cartilage of the joint. 

 It unites below with the two layers of the 

 deep perineal fascia or triangular ligament, be- 

 tween which it gives origin to the vertical 

 compressors urethra, and forms the superior 

 boundary of the pubic arch, the apex of which 

 it rounds off and smoothens. 



The movements of the pubic symphysis are 

 confined to a slightly yielding sliding motion 

 giving elasticity to the resistance of the pelvic 

 ring. 



The obturator or thyroid membrane (g) is a 

 fascial aponeurosis rather than a ligament, 

 which closes in the oval foramen of that name. 

 It is composed of layers of fibres, intermin- 

 gling in a circular direction, and generally 

 congregated more in some places than others. 

 These are attached to the rough narrow bor- 

 der of the descending branch of the ischium 

 externally, but at the internal half of its cir- 

 cumference it is attached to the posterior sur- 

 face of the ascending branch of the ischium 

 and descending branch of the pubis, overlap- 

 ping in this situation the borders of these 

 bones posteriorly. Superiorly, it is inter- 

 rupted by passing over from one edge of the 

 sub-pubic notch to the other, so as to form 

 the lower boundary of a foramen for the pas- 

 sage of the obturator nerves and vessels. 

 Opposite the cotyloid notch its fibres are 

 continued into the capsular ligament invest- 

 ing the hip joint. By its anterior surface, it 

 gives attachment to the obturator external 

 muscle, and, by its posterior surface, to the 

 internal muscle of the same name. It is some- 

 times deficient in one or more places. 



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 

 Ouvier, this oblique direction of the sym- 

 phvsis 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 maybe 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 measurements are, 

 however, considerably greater in the female 

 pelvis, hereafter to be considered. 



The lateral aspects 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 



