Where can I find the text of a poem, perhaps by Don Marquis, about a
man who fell out of an airplane, burst into pieces, and was then put
back together with parts and pieces of other animals. including "the
femur of a lemur"?

Only reference to 'femur of a lemur' I could find was at this page:

http://www.elsbernd.net/matte/SPAM/no.102764.html

It included the reference to:

"except...what's this?...i've discovered...
a femur of a lemur? no.
a thigh of a fly? no."

And is based on a traditional Dig song of archaeologists.

Hope this helps...