
Obsidian possibly used in trephination experiments
1918-1920
1918-1920
1917
1919
circa 1915
1923 - 2015
1920 - 2007
circa 1920
1915
1920
1915
1924
1918
1914-1920
1916
1914
1915
1915
1917
1918
1914
1924
1955; 1830
1915-1917
1918
1914
1914-1918
1918
1915-1918
1916-1917
1922-1923
1922-1923
1922-1923
1922-1923
1921
1920
1914-1918
2000-100 BCE
1914
circa 1920
1914-1918
1923
1914-1924
1914-1924
1914-1918
1914-1918
1914
1914
1914-1918
1914-1918
1922