282 



THE SKELETON. 



ischiatic tuberosity to the same point on the opposite side : the average measurement 

 is three and a half inches in the male and four and three-quarters in the female. 

 Position of the Pelvis. In the erect posture the pelvis is placed obliquely 

 with regard to the trunk of the body : the bony ring, which separates the true 

 from the false pelvis, and which forms the essential part of the pelvis, is placed so 

 as to form an angle of about 60 to 65 with the ground on which we stand. The 

 pelvic surface of the symphysis pubis looks upward and backward, the concavity 

 of the sacrum and coccyx downward and forward, the base of the sacrum in well- 

 formed female bodies being nearly four inches above the upper border of the 

 symphysis pubis, and the apex of the coccyx a little more than half an inch above 

 its lower border. The obliquity is much greater in the foetus and at an early 

 period of life than in the adult. In consequence of this obliquity of the pelvis 

 the line of gravity of the head, which passes through the middle of the odontoid 

 process of the axis and through the points of junction of the curves of the vertebral 

 column to the sacro-vertebral angle, descends toward the front of the cavity, so 

 that it bisects a line drawn transversely through the middle of the heads of the 

 thigh-bones. And thus the centre of gravity of the head is placed immediately 

 over the heads of the thigh-bones on which the trunk is supported. 



Axes of the Pelvis (Fig. 212). The plane of the inlet of the true pelvis will be 

 represented by a line drawn from the base of the sacrum to the upper margin of 

 the symphysis pubis. A line carried at right angles with this at its middle would 

 correspond at one extremity with the umbilicus, and at the other with the middle 

 of the coccyx : the axis of the inlet is therefore directed downward and backward. 

 The axis of the outlet, produced upward, would touch the base of the sacrum, 

 and is therefore directed downward and forward. The axis of the cavity is 

 curved like the cavity itself: this curve corresponds to the concavity of the sacrum 



and coccyx, the extremities being indicated by 

 the central points of the inlet and outlet. A 

 knowledge of the direction of these axes serves to 

 explain the course of the foetus in its passage 

 through the pelvis during parturition. It is also 

 important to the surgeon, as indicating the 

 direction of the force required in the removal of 

 calculi from the bladder, and as determining the 

 direction in which instruments should be used in 

 operations upon the pelvic viscera. 



Differences between the Male and Female 

 Pelvis. The female pelvis, looked at as a whole, 

 is distinguished from the male by the bones being 

 more delicate, by its width being greater and its 

 depth smaller. The whole pelvis is less massive, 

 and its bones are lighter and more slender, and 

 its muscular impressions are slightly marked. 

 The iliac fossae are broad and expanded, and the 

 anterior iliac spines widely separated ; hence the 

 greater prominence of the hips. The inlet in 

 the female is larger than in the male ; it is more 

 nearly circular, and the sacro-vertebral angle 



projects less forward. The cavity is shallower and wider ; the sacrum is shorter 

 and wider, and its lower half forms a greater angle with its upper ; the obturator 

 foramina are triangular, and smaller in size than in the male. The outlet is 

 larger and the coccyx more movable. The spines of the ischia project less in- 



ing chart has been formulated to show the measurements of the pelvis, which are adopted by many 



obstetricians. ED. 



A. P. Obi. Tr. 



Inlet 4 4i 5 



Cavity 4* 4| 4| 



Outlet 5 4J 4" 



plane o. 



FIG. 212. Vertical section of the pel- 

 vis, with lines indicating the axes of the 

 pelvis. 



