180 



THE SKELETON. 



plane. It is smaller than the false pelvis, but its walls are more perfect. For 

 convenience of description it is divided into a superior circumference or inlet, an 

 inferior circumference or outlet, and a cavity. 



The superior circumference forms the brim of the pelvis, the included space 

 being called the inlet. It is formed by the linea ilio-pectinea, completed in front 



FIG. 124. Female pelvis (adult). 



by the crests of the pubic bones, and behind by the anterior margin of the base of 

 the sacrum and sacro-vertebral angle. The inlet of the pelvis is somewhat heart- 

 shaped, obtusely pointed in front, diverging on either side, and encroached upon 

 behind by the projection forward of the promontory of the sacrum. It has three 

 principal diameters : antero-posterior (sacro-pubic), transverse, and oblique. The 

 antero-posterior extends from the sacro-vertebral angle to the symphysis pubis ; 

 its average measurement is four inches in the male, four and three-quarters in the 

 female. The transverse extends across the greatest width of the inlet, from the 

 middle of the brim on one side to the same point on the opposite; its average 

 measurement is four and a half in the male, five and a quarter in the female. 

 The oblique extends from the margin of the pelvis, corresponding to the ilio- 

 pectineal eminence on one side, to the sacro-iliac articulation on the opposite 

 side ; its average measurement is four and a quarter in the male and five in 

 the female. 



The cavity of the true pelvis is bounded in front by the symphysis pubis ; 

 behind, by the concavity of the sacrum and coccyx, which, curving forward above 

 and below, contracts the inlet and outlet of the canal ; and laterally it is bounded 

 by a broad, smooth, quadrangular surface of bone, corresponding to the inner 

 surface of the body of the ischium and that part of the ilium which is below 

 the ilio-pectineal line. The cavity is shallow in front, measuring at the symphy- 

 sis an inch and a half in depth, three inches and a half in the middle, and four 

 inches and a half posteriorly. From this description it will be seen that the 

 cavity of the pelvis is a short, curved canal, considerably deeper on its posterior 

 than on its anterior wall. This cavity contains, in the recent subject, the rectum, 

 bladder, and part of the organs of generation. The rectum is placed at the back 

 of the pelvis, and corresponds to the curve of the sacro-coccygeal column ; the 

 bladder in front, behind the symphysis pubis. In the female the uterus and 

 vagina occupy the interval between these viscera. 



The lower circumference of the pelvis is very irregular, and forms what is 

 called the outlet. It is bounded by three prominent eminences : one posterior, 

 formed by the point of the coccyx ; and one on each side, the tuberosities of the 



