The properties of exteriority and interiority of square matrices with elements from arbitrary Boolean algebra are studied in this paper. The exteriorandinte riorparts formade generatepart of a matrix with zerodeterminant. Itisshown, inparticular, that the setof exteriorparts is a normal setinthe Boolean algebraofall Booleans quarematrices and it is a lower semilattice. The set of interior parts is an upper semilattice. Moreover linear combinations and even polynomials of the interiorities also belong to it.
