The pelvic girdle is a bony structure that connects the lower limbs (legs) to the axial skeleton (spine). It is formed by two hip bones (also called coxal bones or innominate bones), which are joined together at the front by the pubic symphysis and attached to the sacrum at the back. Each hip bone is itself a fusion of three bones: the ilium, ischium, and pubis.

Key labelled parts to include in your diagram:

Ilium: The large, flared upper part of the hip bone. It has a crest (iliac crest) that you can feel at your waist.

Ischium: The lower, posterior part that you sit on. It has a prominent feature called the ischial tuberosity.

Pubis: The anterior part of the hip bone. The two pubic bones meet at the pubic symphysis.

Acetabulum: A deep, cup-shaped socket on the lateral side of the hip bone where the head of the femur (thigh bone) fits to form the hip joint.

Obturator foramen: A large opening between the ischium and pubis, covered mostly by a membrane.

Pubic symphysis: A cartilaginous joint where the two pubic bones meet anteriorly.

Sacroiliac joint: The joint where the ilium articulates with the sacrum.

Function: The pelvic girdle provides strong support for the weight of the upper body when sitting and standing. It also protects the lower abdominal organs, such as the urinary bladder and reproductive organs, and provides attachment points for many muscles.

Related Topics and Formulae

Related Topic: Human Skeleton (Axial and Appendicular)

The human skeleton is divided into the axial skeleton (skull, vertebral column, rib cage) and the appendicular skeleton (limbs and their girdles). The pelvic girdle is part of the appendicular skeleton and, along with the pectoral (shoulder) girdle, connects the limbs to the main body axis.

Related Topic: Joints

The pelvic girdle contains different types of joints. The sacroiliac joint is a slightly movable joint (amphiarthrosis), while the pubic symphysis is a cartilaginous joint. The hip joint (between the acetabulum and femur) is a classic example of a ball-and-socket synovial joint, which allows for a wide range of movement.

Related Topic: Sexual Dimorphism

The female pelvis is generally wider and shallower than the male pelvis. This adaptation provides a larger space (the pelvic inlet and outlet) for childbirth. The angle of the pubic arch is also wider in females.