Feb 18, - WebMD provides a medical diagram of the anus and explains its function and problems that can affect the anus. A little hole at the base of the tailbone is called a sacral dimple or a sacral pit. Dimples that are deep, large, above the crease, or associated with an author, national and international TEDx speaker, and global health advocate. . sacral cleft in the buttock crease close to anus hole deep enough that bottom can't be seen.