<P> The pubic region or pubis is the ventral and anterior of the three parts forming the hip bone . It is divisible into a body, a superior ramus, and an inferior ramus . The body forms one - fifth of the acetabulum . The body forms the wide, strong, medial and flat portion of the pubic bone which unites with the other pubic bone in the pubic symphysis . The fibrocartilaginous pad which lies between the symphysial surfaces of the coxal bones, that secures the pubic symphysis, is called the interpubic disc . </P> <P> The superior pubic ramus is a part of the pubic bone which forms a portion of the obturator foramen . It extends from the body to the median plane where it articulates with its fellow of the opposite side . It is conveniently described in two portions: a medial flattened part and a narrow lateral prismoid portion . </P> <P> The inferior pubic ramus is thin and flat . It passes laterally and downward from the medial end of the superior ramus . It becomes narrower as it descends and joins with the inferior ramus of the ischium below the obturator foramen . </P> <P> The hip bone is ossified from eight centers: three primary, one each for the ilium, ischium, and pubis, and five secondary, one each for the iliac crest, the anterior inferior spine (said to occur more frequently in the male than in the female), the tuberosity of the ischium, the pubic symphysis (more frequent in the female than in the male), and one or more for the Y - shaped piece at the bottom of the acetabulum . The centers appear in the following order: in the lower part of the ilium, immediately above the greater sciatic notch, about the eighth or ninth week of fetal life; in the superior ramus of the ischium, about the third month; in the superior ramus of the pubis, between the fourth and fifth months . At birth, the three primary centers are quite separate, the crest, the bottom of the acetabulum, the ischial tuberosity, and the inferior rami of the ischium and pubis being still cartilaginous . By the seventh or eighth year, the inferior rami of the pubis and ischium are almost completely united by bone . About the thirteenth or fourteenth year, the three primary centers have extended their growth into the bottom of the acetabulum, and are there separated from each other by a Y - shaped portion of cartilage, which now presents traces of ossification, often by two or more centers . One of these, the os acetabuli, appears about the age of twelve, between the ilium and pubis, and fuses with them about the age of eighteen; it forms the pubic part of the acetabulum . The ilium and ischium then become joined, and lastly the pubis and ischium, through the intervention of this Y - shaped portion . At about the age of puberty, ossification takes place in each of the remaining portions, and they join with the rest of the bone between the twentieth and twenty - fifth years . Separate centers are frequently found for the pubic tubercle and the ischial spine, and for the crest and angle of the pubis . </P>

Which bone articulates with the coxal bone to form the hip joint