Which of the following points is located at the medial side of the foot in the head of the first metatarsal bone?

The point located at the medial side of the foot in the head of the first metatarsal bone is indeed Spleen 1 (SP 1). This point, also known as Yinbai, is situated on the medial aspect of the big toe, right at the junction where the skin changes from the dorsal to the plantar side, specifically at the level of the first metatarsal.

It's involved in various clinical applications, such as supporting the spleen function and regulating blood flow, making it essential for practitioners to identify its correct location accurately in practice. The anatomical positioning of SP 1 as described aligns well with the description of being on the medial side of the foot at the head of the first metatarsal, allowing for effective needling and therapeutic application.

In this context, other points mentioned do not meet the criteria of being located at the same anatomical site as SP 1.