Please see question explanation first..
What makes up the difference in the lower limb ?
The upper and lower limbs each contain 30 bones yet we have 8 carpal bones in the upper limb and only 7 tarsal bones in the lower limb.
That would probably be the patella, or kneecap, which is a bone that covers the front part of the joint between the lower part of the femur and the upper part of the tibia and fibula. That would give an extra bone in that particular joint that does not exist in the corresponding joint in the upper arm, the elbow. The elbow consists of the lower part of the humerus connecting to the upper part of the radius and the ulna. The patellas function is to protect the knee and the ligaments holding the knee joint together. There is also more stress on the knee joint than on the elbow, given the knee must support at least 90 percent of the bodys weight. People who are obese have even more stress on the lower joints in the skeletal system. The bones of the tarsals, are larger and fewer in number, given they must support more of the bodys weight. The carpals, on the other hand, are smaller and more in number, to facilitate suppleness and flexibility in the wrist joint, which would give the wrist a multiplicity of motion functions.