
Obsidian possibly used in trephination experiments
1918-1920
1918-1920
1920-1925
1919
1923 - 2015
1920 - 2007
1926
circa 1920
1927
1927
1920
1924
1928
1918
1927
1920-1925
1928
1918
1925
1924
1955; 1830
1918
1918
1925-1928
1928
1924
1927
1926
1922-1923
1922-1923
1921
1922-1923
1922-1923
1921-1926
1925
1923
1924-1927
1934
1921
1920
2000-100 BCE
before 1928
circa 1920
1923
1920-1928
1920-1928
1925
1922
1925-1927
1928
1926