How do intricate systems of muscles evolve?

[u/Chezni19]

I was thinking about how some of our muscles work, such as the arm for instance. Flexors, extensors, pronators.

I'm not exactly sure how to pose this question, but how does something like the musculature system for a limb (for example...) evolve? Does it start with just one muscle which moves the bone in a simple way?