Sacrum & Coccyx

• Sacrum


  the triangular sacrum, which shapes the posterior wall of the pelvis, is formed by 5 fused vertebrae (S1-S5) in adults

  it articulates superiorly w L5 + inferiorly w the coccyx

  laterally, the sacrum articulates, via its auricular surfaces, w the 2 hip bones to form the sacroiliac joints of the pelvis
• Sacral Base & Apex

  the sacral base articulates w the 5th lumbar vertebra + its associated intervertebral disc

  the sacral apex is complementory to the coccyx inferiorly
• Sacral Auricular Surfaces

  the auricular surfaces r located laterally on the sacrum

  each articulates w the auricular surface of the ilium
• Sacral Anterior & Posterior Surfaces

  the sacral anterior + posterior surfaces provide attachment to pelvic ligaments + muscles
• Sacrum = Terminal of the Vertebral Canal

  the sacrum is a large bone located at the terminal part of the vertebral canal, where it forms the posterior aspect of the pelvis

  it is v thick, which aids in supporting + transmitting the weight of the body
• Vertebral Central Canal & Sacral Hiatus

  internally, the central canal of the vertebral column continues along the core of the sacrum + ends at the 4th sacral foramina, as the sacral hiatus

  
• Coccyx


  the coccyx, tailbone, is a small triangular bone

  it consists of 3-5 vertebrae fused together

  the coccyx articulates superiorly w the sacrum

  except for the slight support the coccyx affords the pelvic organs, it is a nearly useless bone