OS COX.E 49 



a body and two branches, or rami. The body joins the ilium, the 

 superior ramus has a short projection called the spine of the pubes, 

 and the inferior ramus extends downward and backward to join 

 the ischium, thus forming the upper part of the pubic arch. The 

 two pubic bones join each other in the median line, forming the 

 pubic symphysis (symphysis pubis). 



Os ilium 



Os pubis 



Os ischii 



Tuberosity 



FIG. 44. HIP-BONE, INTERIOR, BEFORE UNION OF PARTS. (Morris.} 



The os ischii (or the ischium), the lowest part of the hip-bone, 

 has a sharp spine projecting backward, a tuberosity upon which 

 the trunk rests in the sitting position, and a ramus which joins the 

 pubic ramus to complete the pubic arch. 



The ilium, ischium, and pubes united form the hip-bone (os coxae) . 

 Two large notches are seen on the posterior border of the completed 

 bone, separated by the spine of the ischium and called the sciatic 

 notches. The upper one is the greater and the lower one is the lesser 

 sciatic notch. In front of the acetabulum is the obturator foramen, 

 the largest foramen in the skeleton. It is almost entirely closed by 

 the obturator membrane, which is composed of white fibrous tissue. 



THE ARTICULATIONS OF THE PELVIS 



The two hip-bones unite with each other in front at the pubic 

 symphysis, but the sacrum is between them in the back, having 



4 



