Which portion of the pelvis is commonly referred to as the 'sit bones'?

The portion of the pelvis commonly referred to as the "sit bones" is the ischium. This term comes from the fact that when a person is sitting, the weight is often borne by the ischial tuberosities, which are bony prominences on the ischium. The ischium forms the lower back part of the hip bone and contributes to the structure and stability of the pelvis. Understanding this anatomy is particularly important in fields like emergency medical care, where awareness of skeletal structures can assist in injury assessment and treatment, particularly in cases of pelvic fractures or discomfort during sitting.

The ilium is the uppermost and largest part of the pelvis, and while it plays a crucial role in the structure, it is not associated with sitting. The pubis forms the front part of the pelvic bone and is involved in forming the pubic symphysis, which is not related to the sitting position. The sacrum, a triangular bone at the base of the spine, connects to the pelvis but does not provide the sitting support that the ischium does. Therefore, the ischium is the correct answer when identifying the bones that you sit on.