Usually just considered an idea. Some say it's a theory, others a hypothesis. I feel like it's just an idea with NO facts whatsoever.
A link between the skeletal system and the muscular system are tendons, which connect bones to muscles.
A link between the skeletal system and the nervous system is how the vertebrae are linked to the nerves in the spinal cord.
A link between the muscular system and the nervous system is how muscles respond when nerves signal them to after responding to the stimulus and traveling to the brain and back.
O M G i just did that one on Plato
well anyway i think the answer was the the skin because any thing that invades the body is a threat to the immune system.
It is trying to fulfill the social aspect of their lives