The skin depression of the tailbone is mainly manifested as a different degree of depression of the skin in the middle of the tailbone of infants after birth, the diameter of the skin surface can be between 0.5-1 cm, the depth of 0.5-1.5 cm, without secretion, the inner surface of the depression is covered by normal skin, the skin can be seen to be closed at the base of the skin, and the tip of the tailbone can be touched with the fingertip at the base of the skin. Most of them can be gradually flattened with age. This skin depression is a residual body marking during fetal development and is generally of no pathologic significance and requires no treatment. It is not directly related to the occurrence of spina bifida. The author counted 1,652 infants with caudal skin indentation in the clinic, and the incidence of spina bifida was not significantly different from the incidence of spina bifida in the overall population. Spina bifida generally occurs at or above the sacral vertebrae, which is inconsistent with the location of this skin depression. There is also a significant difference between the caudal skin depression and the dermal sinus, which manifests as a cutaneous fistula that is usually small, mostly pinpoint, sometimes with secretions, and cannot be visualized or palpated at its base. Clinically feasible spinal MRI to distinguish.