In a chicken wing, the tricep has to contract to fully extend the wing. So for the chicken to fold its wing, the bicep must contract.
The cartilage on the ends of the bone is very smooth to touch. An observation about the chicken wing is that there is skin between the shoulder and the tip of the wing. This is probably to help catch air so the chicken can fly short distances.
When the bicep contracts, the tendon that connects the muscle to the bone makes the wing to fold. When the bicep stretches, the wing will be fully extended. This is exactly the same in a human arm. The reason there is a radius and ulna is so that the end of the wing can move alone, without requiring the rest of the arm to move. These bones are very similar to the bones in our forearms, allowing our wrists to not only move up and down, but right and left as well.
To create a downward force, the wing has to move up and down quickly, but also be able to tilt backwards to slow the chicken down when landing. This is why the arm is connected to the rest of the body via a ball and socket joint. The ball and socket joint also is in a human’s shoulder. It gives us almost full motion of our arms.
The bicep is the strongest muscle in the human arm. When the bicep is contracting, flexed or being put under load, the arm folds. When you pick something up, typically you do it with the inside of your forearm facing upwards. The reason we do this is because it’s the easiest way to pick heavy things up. That is why our bicep is the strongest muscle in our arm.