[Letter from Dr. Francisco del Rio y Cañedo to John J. Herrera - 1951-09-19], letter, September 19, 1951; (https://texashistory.unt.edu/ark:/67531/metapth250200/m1/2/: accessed July 16, 2024), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; .