i Register
In some senses, musculous is marked as archaic, obsolete. Watch for register when choosing this word.
adj
Made up of muscle or muscle tissue; muscular.
[T]he rest of the capacity of the clusters was […] in others fill'd with some kind of substance; in blue Flies, with a reddish musculous substance, with fibres tending from the center or bottom outwards […].
Characterised by well-developed muscles; muscular, muscly.
Pertaining to muscle; involving the use of muscles; muscular.