Sacrum and coccyx form the posterior bony boundary of the pelvis. Watch this video and learn about the gross features of the sacral bone in this video. 0.00 introduction 0.34 articulations 0.48 fusion of 5 vertebrae 1.14 pressure ulcers 1.21 male vs female sacrum 1.39 features of the dorsal surface 4.23 features of the anterior surface