Hydroschendyla submarina, selection of micrographs of transverse sections through the head from anterior to posterior. A Section through the anterior head part, showing the mandibulo-tentorial complex at the level of the epipharyngeal bar B Section through the mandibulo-tentorial complex (right side of head) at the level of the junction between epipharyngeal bar and supramandibular arch. C Section through the mandibulo-tentorial complex (left side of head) between the levels shown in B and D. D Section through posterior part of tentorium and mandible (right side of head) at the level of the mesial interconnection of the mandibles by muscle 26. Numbers refer to muscles as listed in Table 1. Abbreviations: br brain cl clypeus, cl-ecr clypeo-epicranial muscle eb epipharyngeal bar of tentorium, ecr epicranium hy hypopharynx lbs labral sidepiece mb mandibular base md mandible mxI first maxilla ph pharynx pp posterior process of tentorium sma supramandibular arch of tentorium sog subesophageal ganglion tb transverse bar of tentorium tmxII telopodite of second maxilla.