Final answer:
The iliac crests align with the fourth lumbar vertebra (L4). They are part of the superior margin of the ilium and serve as attachment points for muscles and ligaments.
Step-by-step explanation:
The iliac crests, significant bony landmarks found along the waist, align with the fourth lumbar vertebra (L4) in the human body. These crests serve as attachment points for muscles and ligaments and help to form the superior part of the hip bone, which includes the ilium. The ilium is part of the hip bone, which also comprises the ischium and pubis, with the ilium forming the large fan-like region of the hip bone.
The superior margin of the ilium is the iliac crest, which is level with the L4 vertebra. The crests terminate anteriorly as the anterior superior iliac spine and posteriorly as the posterior superior iliac spine. Muscles of the thigh and strong ligaments supporting the sacroiliac joint attach to these spines.