External and internal features of the thorax of alate and wingless morphs of Zorotypus hubbardi and Z. weidneri were examined and described in detail. Three-dimensional computer reconstructions were carried out based on microtome section series. Skeletal structures are less sclerotised in the wingless specimens and the limits of sclerites are indistinct. The alate morphs are almost exclusively characterised by plesiomorphic features and their thoracic morphology is probably close to the neopteran groundplan. The skeletal structures are very similar to the condition found in Plecoptera and the muscle system comprises nearly the maximum number known in representatives of Neoptera. Based on the morphological investigation of Zorotypus and comparisons with data for other taxa from the literature, a new consistent nomenclature for the thoracic muscular system of Neoptera is proposed. The few derived features found in the thoracic skeleto-muscular apparatus of Zorotypus are mostly autapomorphic. The obtained data do not clearly indicate the systematic placement of the order. However, the arguments for a close relationship with Endopterygota or Dictyoptera, respectively, are refuted.