Can anyone help me identify this YA SF series?

[RealHuman]

I'm struggling to remember the name/author of a science fiction series I read as a kid. I think it was written by one of the big hitters - someone like Asimov or Heinlein. It was a sort of space police kind of story, with a main character who'd lost his arm and had an amusingly-different-from-his-own-body arm transplanted on to him. Also I think one of the books had a cover illustration of a planet that looked like a skull, though I may be confusing it with another series.

Does anyone have any ideas? I'm drawing a blank with all my search terms.

My DH thinks it might be Bill the Galactic Hero by Harry Harrison? It didn't have a skull on the front cover but he thinks another of his books - maybe Deathworld? - did.

Thanks granulated (and your DH). I looked up Bill The Galactic Hero on Wikipedia and it does sound awfully familiar - perhaps I'm mixing up aspects from that series with another one? I'm sure though that I remember the main character in the series I'm thinking of as having a large, more muscular arm(s?) which had been transplanted from a donor of a different race.

DH says that Bill gets his left arm replaced by the right arm of Tembo, another soldier oif another race. As the story goes on, he gets tusks implanted and shoots off his own foot which he gets replaced with a robot foot!

Aha, they didn't mention that on the Wikipedia article - that's it, then! Thanks so much (and I'm impressed by your DH's memory ) I know what I'm re-reading this week, then...

Great! My DH loves sci fi so has got a good memory for stuff like that. I can't stand it when I remember details of a book but just can't find out what it is, so i feel chuffed that I had some part in helping! Enjoy your re-reading!