Human: What is the difference between a femur, a tibia and a fibula? Assistant: 
The differences are in their lengths and functions. A femur is the largest bone in the body and is located in the upper leg. It connects to the hip joint and helps to support the weight of the body. A tibia is the second longest bone in the body and is located in the lower leg. It connects to the knee joint and helps to support the weight of the body. Lastly, a fibula is the third longest bone in the body and is located in the lower leg. It connects to the ankle joint and helps to support the weight of the body.