1940's short story: "The Black Brain" by Robert Bloch

Thanks to a generous fan of old pulp magazines at the Internet Archive, you can read or download “The Black Brain,” a short story penned by horror, crime and science fiction writer Robert “Psycho” Bloch under the pseudonym Tarleton Fiske, as it was published in the March 1943 issue of Fantastic Adventures magazine.

"If this was the brain of a Martian dead millions of years, how could it be alive?
How could it keep on growing?"