Final answer:
The "keystone" bone of the medial longitudinal arch in the foot is the talus, which is centrally positioned to support body weight and distribute it across the foot.
Step-by-step explanation:
The tarsal bone often referred to as the "keystone" of the medial longitudinal arch in the foot is the talus. The talus is crucial because it receives the weight of the body and is located at the top of the arches. It is superiorly linked to the tibia and fibula at the ankle joint. Inferiorly, it connects to the calcaneus bone and anteriorly with the navicular bone. This strategic position allows the talus to act as a major supporting structure, balancing and distributing the body's weight across the foot.
The medial longitudinal arch is important for shock absorption and providing a springy base for propulsion during walking and running. Other tarsal bones - including the calcaneus, navicular, cuboid, and three cuneiform bones - also form the posterior structure of the foot, but the talus is the key element in the medial longitudinal arch's construction.