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Pecs come from having arms configured to be moved in multiple axes. If you didn't have pecs, you wouldn't be able to push your arms forcefully in front of you. Think of the classic advice (not entirely a good idea, mind you) on dealing with aggressive dogs: grab their front legs and pull them apart, ripping tendons, ligaments, and other painful goodies. They can't resist that because they don't have pectoral muscles like we do.

So wookies would have pecs. Their arms are configured, as we see, in a similar manner to ours. Deltoids and lats (and other muscles, obviously) to move the arms up and down, pectorals and rhomboids and serratus(es/i) and teres(i) (and other muscles, obviously) to move them front and back.

Closest analogue for a wookie to an earth animal is going to be a marsupial. They are arboreal, they get really angry and rage about but are supposedly peaceful, and it seems like they only have one kid at a time (we only ever saw a female wookie with one lump). They even have the noses of koalas. Thus they would likely have pouches, so maybe a nipple analogue would be buried in the pouch somewhere down by the abdomen.