and is characterized by few and shallow sulci and a thin covering of leptomeninges, with fine hair-like superficial cerebral veins reminiscent of a foetal brain (Osman-Hill, 1945). The corpora quadrigemina, especially the inferior, are prominent suggesting auditory sensitivity. The cerebellum is well developed and possesses large floccular lobes composed mainly of the paraflocculus, probably associated with pronounced swimming and equilibratory activities (Harrison & King, 1%5). Native dugong hunters consider that the hearing of dugongs is acute but that their visual powers are less developed (Prater,1929; Jarman, 1966; Roughsey, 1971). The unusual arrangement of the ear ossicles has been described by Robineau (1%5) and their vibrations measured by Fleischer (1971).