Shema yaase adam oros aviv v'imo shtichin lachamor

The gemara on 55a says that a dead person's skin is only tamei m'drabonnon and the reason they made it tamei was so that a person shouldn't make his parents' skin into shtichin lachamor. Rashi says that means a donkey's saddle.

Tosafos asks that it's asur b'hanaa so why the need for the gezeira? They have two answers. One is that skin isn't really asur b'hanaa. The other answer is that people are more likely to not do something because they don't want to be tamei than they are even if there is an isur d'oraysa of hanaa!

The Ritva is still bothered by two questions.
1. Who would use their dead parents' skin as a saddle?!?
2. Why does the gemara use the example of the parents' skin?

Tosafos in chullin 122a answers the second question by saying that it just uses the most likely example. It's unlikely that he'd be able to get someone else's skin to use so the only skin he has readily available is his parents'.

The Ritva though says that we're not talking about a saddle at all. We're talking about a decorative piece. Some people will honor their parents by placing their skin onthe living room wall. Therefore the Rabbonon felt the need to make the gezeira. The Ritva's pshat is nice except for one problem - the gemara says shtichin lachamor. The footnote on the bottom of the Mossad Harav Kook edition says that the Ritva and other Rishonim didn't have that girsa. It is true that the same gemara is in chullin 122a and the word chamor is left out there.