The largest recorded brain in the U.S is said to belong to one Edward H. Rulloff. This guy wrote a book on his theory of the origin of languages shortly before his execution. What was his theory? Is the book available in an online form somewhere?
It is not clear that, whatever Ruloff's ideas about language they were actually formulated in book form - printed book or complete manuscript. Nothing appears to have been publshed under his name.
He was the subject of a book:
Life, trial and execution of Edward H. Ruloff : the perpetrator of eight murders, numerous burglaries and other crimes; who was recently hanged at Binghamton, N.Y (1871) (Reprint) [Leatherbound] Rulloff, Edward H. defendant. (Edward Howard), 1819-1871,
Published by Pranava Books (2020).*
I doubt whether much if any philological reflection is to be found here but I have not been able to access the text, so can't reassure you one way or the other. I doubt if the weight of his brain is an index to the weight of his ideas, but one never knows.