128 



PRACTICAL ANATOMY. 



extremity is continuous with the ilium and ischium, the 

 lines of union passing through the acetabulum, a large, 

 cup-like, articular cavity on the outer side of the os in- 

 nominatum. Of the acetabulum the ilium makes two- 

 fifths, the pubes one-fifth, and the ischium two-fifths. 



The descending ramus, broad above, becomes thinner, 

 and forms the inner boundary of the obturator foramen. 



FIG. 59. OS INNOMINATUM, INNER SURFACE. 



Its anterior surface is rough, for the attachment of mus- 

 cles; posteriorly it is smooth, and enters into the formation 

 of the anterior wall of the pelvis. Its inner border pre- 

 sents the pudic groove, a shallow groove formed by the 

 eversion of the anterior margin of the ramus ; it accom- 

 modates the pudic vessels and nerve. Its outer border is 

 sharp, and forms part of the circumference of the obtu- 



