
Obsidian possibly used in trephination experiments
1918-1920
1918-1920
1917
1919
1920-1925
circa 1915
1915-1925
1926
circa 1920
1927
1927
1915
1920
1915
1924
1928
1918
1914-1920
1915-1925
1916
1914
1915
1927
1915
1920-1925
1917
1928
1918
1925
1914
1924
1955; 1830
1915-1917
1918
1914
1914-1918
1918
1915-1918
1913-1923
1925-1928
1916-1917
1928
1922-1923
1922-1923
1922-1923
1922-1923
1921
1920
1914-1918
2000-100 BCE
1914