
Obsidian possibly used in trephination experiments
1918-1920
1918-1920
1935
1935
1920-1925
1917
1934
1919
1923 - 2015
1920 - 2007
1926
1931
circa 1920
1927
1927
1920
1924
1935
circa 1930
1928
1918
1920-1929
1934
1935
1922
1932
1934-1935
1934
1931
1931
1927
1925
1930
circa 1930
1920-1925
1917
1928
1918
1932
1933
1935
1925
1924
1955; 1830
1935
1918
1918
1925-1928
1927-1929
1928
1924