230 A MANUAL OF ANATOMY 



being transverse. The diameters of the brim are antero-posterior 

 or conjugate, transverse, right oblique, and left oblique. The antero- 

 posterior or conjugate diameter extends from the upper border of 

 the symphysis pubis to the sacral promontory ; the transverse, 

 from one ilio-pectineal line to the opposite, across the widest part 

 of the brim ; and the oblique, from one sacro-iliac articulation to 

 the ilio-pectineal eminence of the opposite side. The oblique 

 diameters are called right and left from the sacro-iliac articulations 

 whence they extend. 



The cavity is bounded in front by the bodies and rami of the 

 pubic bones, behind by the sacrum and coccyx, and laterally 

 by an extensive osseous plane, formed chiefly by the pelvic surface 

 of the ischium, but also by that of the ilium, and terminating 

 below in the incurved ischial spine. It is shallow in front, where 

 its depth is from i| to 2 inches, but deep behind, where it measures 

 about $\ inches, following the curve of the sacrum. The plane 

 of the anterior wall is oblique, being directed downwards and 

 backwards. The posterior wall is curved, and at its upper part 

 looks mainly downwards. The lateral wall is divided into two 

 parts by an indistinct line extending downwards and backwards 

 from the ilio-pectineal eminence to the spine of the ischium. 

 These parts are spoken of as the anterior and posterior inclined 

 planes of the ischium, the anterior looking slightly forwards and 

 the posterior slightly backwards. The conjugate diameter of the 

 cavity extends from the centre of the symphysis pubis to the 

 upper margin of the third sacral segment ; the transverse, from 

 a point corresponding to the lower margin of the acetabulum 

 on one side to the corresponding point on the other ; and the 

 oblique, from the centre of the great sacro-sciatic foramen on 

 one side to the centre of the obturator membrane on the other. 



The outlet presents three prominences, namely, the tuber ischii at 

 either side, and the tip of the coccyx in the median line posteriorly. 

 Its boundaries, at either side from before backwards, are as follows : 

 the lower border of the symphysis pubis, inferior ramus of os pubis, 

 ramus of ischium, tuber ischii, great sacro-sciatic ligament in the 

 recent state, and tip of the coccyx. In front of an imaginary line 

 connecting the ischial tuberosities is the subpubic arch, which is 

 bounded at either side by the ischio-pubic ramus, and above by 

 their meeting to form the subpubic angle. The arch is occupied 

 by the triangular ligament of the urethra, and its plane is directed 

 downwards and backwards. The conjugate diameter of the outlet 

 extends from the lower border of the symphysis pubis to the tip 

 of the coccyx, the transverse from one tuber ischii to the other, and 

 the oblique from the middle of the lower border of the great sacro- 

 sciatic ligament on one side to the place of union between the 

 inferior pubic and ischial rami on the other. 



The Inclination of the Pelvis. — In the erect posture the plane of 

 the pelvic brim forms with the horizontal an angle of from 50 to 

 60 degrees, and the base^oi- -ttre^ s.icrura is about 3I inches above the 



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