THE BONES OF THE LOWER EXTREMITY 95 



THE TRUE PELVIS. This is the real bony basin, 

 situated below the oblique plane which divides the 

 prominence of the sacrum, iliopectineal line, and sym- 

 physis pubis. It is smaller than the false pelvis. For 

 description it presents a superior circumference or inlet, 

 an inferior circumference or outlet, and a cavity. The 

 superior circumference forms the brim of the pelvis, 

 the heart-shaped space being called the inlet. 



FIG. 46 



Crest fff ilium--- 

 Sup. spine of 



Inf. spine of'iliu. 



Obturator foramen, } 

 Body of ischiujJi 



fuoerosity ofisckium ... 

 Ramus of ischium 



-..Spine of ischium 



ftamus of pubic tone 



' -Symphysis pubes 



Male pelvis from in front and below. 



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; 

 laterally it is bounded by the inner surface of the 

 ischium and that part of the ilium which is below 

 the iliopectineal line. It is shallow in front, measuring 

 If inches in depth at the symphysis, 3J inches in the 

 middle, and 4J inches posteriorly. 

 The'^lower circumference or outlet is irregular in shape. 

 Bounded by three eminences the point of the coccyx 

 behind, and the tuberosities of the ischia on either side. 

 The eminences are separated by three notches: one in 



