The ilium is the uppermost and largest bone of the pelvis. It is divisible into two parts, the body and the ala; the separation is indicated on the top surface by a curved line, the arcuate line, and on the external surface by the margin of the acetabulum.
The iliac crest is the superior border of the wing of ilium and the superolateral margin of the greater pelvis. It has a large amount of red bone marrow, and thus it is the site of bone marrow harvests to collect the stem cells used in bone marrow transplants. The iliac crest is also considered the most ideal donor site for bone grafting when a large quantity of bone is needed.
The anterior superior iliac spine (ASIS) is a bony projection of the iliac bone and an important landmark of surface anatomy. It refers to the anterior extremity of the iliac crest of the pelvis, which provides attachment for the inguinal ligament, and the sartorius muscle.
The anterior inferior iliac spine (abbreviated: AIIS) is a bony eminence on the anterior border of the hip bone, or, more precisely, the wing of the ilium.
The acetabulum is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint. Three bones of the hip bone come together to form the acetabulum; the ischium, the ilium, and the pubis.
The pubic bone is the most anterior of the three principal bones composing either half of the pelvis. The body forms one-fifth of the acetabulum, contributing by its external surface both to the lunate surface and the acetabular fossa. Its internal surface enters into the formation of the wall of the lesser pelvis and gives origin to a portion of the obturator internus.
The pubic symphysis or symphysis pubis is the midline cartilaginous joint uniting the superior rami of the left and right pubic bones.
The obturator foramen is the hole created by the ischium and pubis bones of the pelvis through which nerves and blood vessels pass. Through the canal the obturator artery, obturator vein and obturator nerve pass out of the pelvis.
The ischium forms the lower and back part of the hip bone. It is divisible into three portions. These are the body of the ischium, the superior ramus of the ischium and the inferior ramus of the ischium.
The sacrum is a large, triangular bone at the base of the spine and at the upper, back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and its lower part with the coccyx.
The coccyx, commonly referred to as the tailbone, is the final segment of the vertebral column. It is comprised of three to five separate or fused vertebrae below the sacrum.
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