What is the name of the four small fused vertebrae at the base of the spinal column?

The four small fused vertebrae at the base of the spinal column are referred to as the coccyx, commonly known as the tailbone. This structure is composed of several small bones that have fused together. The coccyx serves several important functions, including providing support when a person is sitting and acting as an attachment site for ligaments and muscles in the pelvic region. Its position at the end of the vertebral column makes it a critical component of the spinal anatomy.

The other choices represent different anatomical structures unrelated to the vertebral column. The canthus refers to the corner of the eye where the upper and lower eyelids meet, the cornea is the clear front part of the eye that covers the iris, and a cataract is a condition that leads to the clouding of the lens of the eye. Each of these terms relates to different aspects of anatomy but does not pertain to the vertebrae or spinal structure.