Every finite, self-dual, regular (or chiral) 4-polytope of type {3, q, 3} has a trivalent 3-transitive (or 2-transitive) medial layer graph. Here, by dropping self-duality, we obtain a construction for semisymmetric trivalent graphs (which are edge- but not vertex-transitive). In particular, the Gray graph arises as the medial layer graph of a certain universal locally toroidal regular 4-polytope. s: semisymmetric graphs, abstract regular and chiral polytopes. AMS Subject Classification (1991): Primary: 05C25. Secondary: 51M20. ∗Supported by the NSERC of Canada, grant 4818 †Supported by Ministry of Higher Education, Science and Technolgy of Slovenia grants P1-0294,J1-6062,L1-7230. ‡Supported by NSA-grant H98230-05-1-0027 §Supported by the NSERC of Canada, grant 8857 1