Final answer:
The pelvic girdle consists of the hip bones, which are each formed by the fusion of three bones: the ilium, ischium, and pubis. These bones connect anteriorly at the pubic symphysis and posteriorly at the sacroiliac joints with the sacrum and coccyx to form the stable, weight-bearing pelvis.
Step-by-step explanation:
The pelvic girdle is best understood as a set of bones that lay the foundation for the lower part of the body’s skeleton. It is not formed by the articulation of the hip bones and the sacrum as suggested in the student's question. Instead, the pelvic girdle is composed primarily of the two large hip bones or coxal bones, which are each formed by the fusion of three bones: the ilium, ischium, and pubis. These hip bones join anteriorly at the pubic symphysis and posteriorly at the sacroiliac joints with the sacrum, which is part of the axial skeleton. Together with the coccyx, they form the pelvis, a bony structure that provides stability, bears the weight of the upper body, and allows for the connection and locomotion of the lower limbs.
In contrast, the pectoral girdle relates to the upper body and consists of the clavicles and scapulae, which are designed to allow for a wide range of motion. The design of the pelvic girdle ensures stability and weight bearing necessary for upright posture and locomotion, contrasting with the high mobility of the pectoral girdle that enables arm and shoulder movement.