The part that attaches in front to the tuberosity of the navicular and the associated margin of the plantar calcaneonavicular ligament (spring ligament), which connects the navicular bone to the sustentaculum tali of the calcaneus bone behind, is the tibionavicular part of the medial ligament.
The tibiocalcaneal part, which is more central, attaches to the sustentaculum tali of the calcaneus bone.