Let {p, q, r} be the regular 4-dimensional poly tope for which each face is a {p, q} and each vertex figure is a {q, r}, where {p, q}, for example, is the regular polyhedron with p-gonal faces, q at each vertex. A Petrie polygon of {p, q} is a skew polygon made up of edges of {p, q} such that every two consecutive sides belong to the same face, but no three consecutive sides do. Then a Petrie polygon of {p, g, r} is defined by the property that every three consecutive sides belong to a Petrie polygon of a bounding {p, q}, but no four do. Let hPqr be the number of sides of such a polygon, and gp,q,r the order of the group of symmetries of {p, g, r}.