
Obsidian possibly used in trephination experiments
1918-1920
1918-1920
1917
1919
1920-1925
1926
circa 1920
1927
1927
1920
1924
1928
1918
1920-1929
1927
1920-1925
1917
1928
1918
1925
1924
1955; 1830
1918
1918
1925-1928
1928
1922-1923
1922-1923
1922-1923
1922-1923
1921
1920
1924
1927
1926
1921
1920-1929
1926
1923
1924-1927
1934
2000-100 BCE
before 1928
circa 1920
1923
1925
1922
1927-1929
1925-1927
1928
1920