Anatomy of the Lower Limb and Evolution of Land Locomotion

Anatomy of the Lower Limb and Evolution of Body Design for Land Locomotion

• The lower limb comprises the thigh, leg, and foot and consists of the femur, patella, tibia, fibula, tarsals, metatarsals, and phalanges.
• Bones of the lower limb are thicker and stronger to support the entire weight of the body and the forces from locomotion.
• The femur is the longest, heaviest, and strongest bone in the body, forming the hip joint at the proximal end and the knee joint with tibia and patella at the distal end.
• The patella is a triangular bone that lies anterior to the knee joint, embedded in the tendon of femoral extensors, and improves knee extension.
• The tibia is a large bone of the leg located below the knee that articulates with the femur, fibula, and tarsal bones and transmits the weight of the body to the foot.
• The fibula parallels and articulates with the tibia, does not bear weight or articulates with the femur, and forms the lateral part of the ankle joint.
• The tarsals are seven bones of the ankle that transmit body weight from tibia and fibula to the foot, while metatarsals are five bones of the foot, and phalanges are 14 bones of the toes.
• The transition of vertebrates onto land required changes in body design, including strengthening and ossification of limbs due to gravity and lack of buoyancy, and axial skeleton changes.
• The loss of direct attachment between pectoral girdle and head reduced jarring to the head caused by limb impact on the ground.
• Early tetrapods moved limbs splayed out to the side, requiring large muscles to move the limbs towards the midline, almost like walking while doing push-ups, which is not an efficient use of energy.
• Later tetrapods have their limbs placed under their bodies, requiring less force to move forward, resulting in decreased adductor muscle size and increased range of motion of scapulae.
• The femur and humerus were rotated so that the limbs and digits pointed forward in the direction of motion, producing a stride that is more efficient for moving over land.