They are both about death, both with skulls and other bits and pieces, but two very different exhibitions.
“Doctors”, etc., at the Museum of London gives a fascinating history of dissection in medicine (with lots of dissected bits of body) – excellent but it costs (£9 + suggested donation + online booking fee).
“Death” at the Wellcome Collection is more limited (one man’s personal collection of art related to the theme of death) and is not as good as previous more ambitious exhibitions such as “Dirt,” but it is free.
Both museums also have very good permanent, free exhibitions, both highly recommended.