
Obsidian possibly used in trephination experiments
1918-1920
1918-1920
1917
1919
circa 1915
circa 1920
1915
1920
1915
1918
1914-1920
1914-1918
1916
1914
1915
1912
1915
1917
1918
1912
1914
1955; 1830
1915-1917
c.1912
1918
1914
1914-1918
1918
1915-1918
1916-1917
1915
1915
1934
1920
1914-1918
1914-1918
2000-100 BCE
1914
1914-1918
circa 1920
1920
1914-1918
1913
1914-1918
1914-1918
1917-1918
1914
1914
1914-1918
1914-1916
1920