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The origin, course and termination of the corticospinal tracts of the Tasmanian potoroo (Potorous apicalis).

The corticospinal tracts ofmany placental mammals have been studied in detail by employing modern selective silver techniques (see Martin, Megirian & Roebuck, 1970 for a partial list of the forms studied). Such studies show that corticospinal fibres vary as to their origin, position and caudal extent within the spinal cord and their precise area of termination. In contrast, similar studies on the wide variety of available marsupials are relatively scarce. Previous studies on the polyprotodont North American opossum, Didelphis marsupialis virginiana, (Martin & Fisher, 1968) and the diprotodont brush-tailed possum (phalanger), Trichosurus vulpecula, (Martin et al. 1970) indicate that the corticospinal tracts of these two marsupials vary in size, caudal extent and termination. The present study was designed to evaluate further the question of variation in marsupial corticospinal tracts by studying them in another diprotodont family and in. a species with an entirely different habitat and method of ambulation from that of the brush-tailed possum. The Tasmanian potoroo (Potorous apicalis) (Fig. 1) was chosen for comparison because, unlike the brush-tailed possum, which is adapted well for arboreal life, it is capable of moving rapidly on the ground by hopping. In addition the potoroo is small, easily handled, and readily available in Tasmania.