94 PELVIS. 



the ossa ilii, and separated from the true pelvis by the linea ilio- 

 pectinea. The true pelvis is all that portion which is situated be- 

 neath the linea ilio-pectinea. This line forms the margin or brim of 

 the true pelvis, while the included area is called the inlet. The form 

 of the inlet is heart-shaped, obtusely pointed in front at the symphysis 

 pubis, expanded on each side, and encroached upon behind by a pro- 

 jection of the upper part of the sacrum, which is named the pro- 

 montory. The cavity is somewhat encroached upon at each side by a 

 smooth quadrangular plane of bone, corresponding with the internal 

 surface of the acetabulum, and leading to the spine of the ischium. In 

 front are two fossae around the obturator foramina, for lodging the ob- 

 turator internus muscle, at each side. The inferior termination of the 

 pelvis is very irregular, and is termed the outlet. It is bounded in 

 front by the convergence of the rami of the ischium and pubes, which 

 constitute the arch of the pubes ; on each side by the tuberosity of the 

 ischium, and by two irregular fissures formed by the greater and lesser 

 sacro-ischiatic notches ; and behind by the lateral borders of the sa- 

 crum, and by the coccyx. 



The pelvis is placed obliquely with regard to the trunk of the body, 

 so that the inner surface of the ossa pubis is directed upwards, and 

 would support the superincumbent weight of the viscera. The base 

 of the sacrum rises nearly four inches above the level of the upper 

 border of the symphysis pubis and the apex of the coccyx, some- 

 what more than half an inch above its lower border. If a line were 

 carried through the central axis of the inlet, it would impinge by one 

 extremity against the umbilicus, and by the other against the middle 

 of the coccyx. The axis of the inlet is therefore directed downwards 

 and backwards, while that of the outlet points downwards and forwards, 

 and corresponds with a line drawn from the upper part of the sacrum, 

 through the centre of the outlet. The axis of the cavity represents a 

 curve, which corresponds very nearly with the curve of the sacrum, the 

 extremities being indicated by the central points of the inlet and outlet. 

 A knowledge of the direction of these axes is most important to the 

 surgeon, as indicating the line in which instruments should be used in 

 operations upon the viscera of the pelvis, and the direction of force in 

 the removal of calculi from the bladder ; and to the accoucheur, as 

 explaining the course taken by the foetus during parturition. 



There are certain striking differences between the male and female 

 pelvis. In the male the bones are thicker, stronger, and more solid, 

 and the cavity deeper and narrower. In the female the bones are 

 lighter and more delicate, the iliac fossae are large, and the ilia ex- 

 panded ; the inlet, the outlet, and the cavity, are large, and the 

 acetabula farther removed from each other ; the cavity is shallow, 

 the tuberosities widely separated, the obturator foramina triangular, 

 and the span of the pubic arch greater. The precise diameter of the 

 inlet and outlet, and the depth of the cavity, are important consider- 

 ations to the accoucheur. 



The diameters of the inlet or brim are three : 1 . Antero- posterior, 



