Bones of sailors on bottom of Mississippi (5)
I believe the answer is:
tarsi
'bones' is the definition.
(bones of the foot)
'sailors on bottom of mississippi' is the wordplay.
'sailors' becomes 'tars' (tar is a kind of sailor).
'on bottom of' indicates one should take the final letters.
The last letter of 'mississippi' is 'i'.
'tars'+'i'='TARSI'
'of' acts as a link.
(Other definitions for tarsi that I've seen before include "Parts of skeleton" , "collections of bones?" , "Bones of the ankles and heels" , "parts of leg" , "Ankle bones" .)