Final answer:
Infants have three separate regions in their hip bones: ilium, ischium, and pubis. These parts are joined by cartilage that ossifies and fuses into one hip bone by the late teenage years.
Step-by-step explanation:
Infants and children have hip bones that are composed of three separate regions: the ilium, ischium, and pubis. These regions are initially connected by cartilage, forming structures called synchondroses. As the child grows into adolescence, the synchondroses gradually ossify to form permanent joins called synostoses, fusing the bones together into a single hip bone. The process of fusion usually completed by the late teenage years, resulting in each adult hip bone being one single structure consisting of three combined parts.
The fusion of the hip bones plays an important role in human development as it contributes to the stability and strength of the pelvic girdle, which supports the upright posture and facilitates walking. It's also significant in the context of childbirth, as the fused pelvic architecture is different in males and females, affecting the birthing process.