What are the differences in the structure of the skeleton of the upper and lower extremities? How can this be explained?

The upper and lower limbs differ in their structure in humans. Also, they have some similarities. The bones that form the limbs are tubular. They are the most durable. This is necessary because the limbs are often heavily loaded. The upper limbs have developed and long phalanges of the fingers. This allows a person to do a variety of jobs. We also have a well-developed thumb. The bones of the lower limbs are thicker and larger. This is due to the fact that we use them for movement.