Final answer:
The coccygeus muscle originates from the ischial spine and not the sacrum or ventral rami S4-S5.
Step-by-step explanation:
The origin of the coccygeus muscle is the ischial spine. The coccygeus, together with the levator ani muscle, forms part of the pelvic floor and plays a role in supporting pelvic viscera. This muscle, sometimes known as ischiococcygeus, acts to pull the coccyx forward after it has been reflected posteriorly during defecation or childbirth. Contrary to the coccyx, which is derived from the fusion of four coccygeal vertebrae, the coccygeus muscle originates specifically from the ischial spine of the hip bone.