The muscles of the muscular system keep bones in place; they assist with movement by contracting and pulling on the bones. To allow motion, different bones are connected by joints which are connected to other bones and muscle fibers via connective tissues such as tendons and ligaments.
Answer:
mutualism and parasitism
Examples:
mutualism: crocodiles and birds
parasitism: mosquitoes and humans
The external ear structure is called the Pinna.
The Pinna helps to channel sound waves into the ear.
Many animals have the ability to move their pinna towards the direction of sound.
I have attached an image of a dog's ear to show you the external structure called the Pinna.
I hope this helps! I'm happy to answer any other questions you might have :)
[Image sourced from: https://www.msdvetmanual.com/dog-owners/ear-disorders-of-dogs/ear-structure-and-function-in-dogs]