The lines joining the vertices of a tetrahedron to the centroids of the opposite faces are called medians. Commandino's theorem states that the four medians of a tetrahedron concur in a point which divides each tetrahedron median in the ratio 1:3, the longer segment being on the side of the vertex of the tetrahedron.
Tetrahedron Median
See also
Commandino's Theorem, TetrahedronExplore with Wolfram|Alpha
References
Altshiller-Court, N. Modern Pure Solid Geometry. New York: Chelsea, p. 51, 1979.Referenced on Wolfram|Alpha
Tetrahedron MedianCite this as:
Weisstein, Eric W. "Tetrahedron Median." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/TetrahedronMedian.html