What is the insertion muscle of cuneiform and first metatarsal?

The muscle that inserts on the cuneiform and first metatarsal is the Tibialis Posterior.

Here's why:

* Tibialis Posterior: This muscle originates from the posterior surface of the tibia and fibula. Its tendon runs behind the medial malleolus (ankle bone) and inserts on the plantar surface of the navicular bone, the three cuneiform bones, and the base of the second, third, and fourth metatarsals.

Therefore, the tibialis posterior plays a crucial role in supporting the medial arch of the foot and in inverting (turning inwards) the foot.