A cyto-architectonic description of the thalamus of the tammar wallaby, Macropus eugenii.

Very few studies are available on the cyto-architectural features of the thalamus of metatherian mammals. Most of these studies describe the thalamus of a polyprotodont metatherian, the North American opossum, Didelphis virginiana. Studies on diprotodont metatherians are fewer still. There are two descriptions of the thalamus of the Australian possum Trichosurus vulpecula. The only part of the thalamus that has been described in the wallabies is the lateral geniculate nucleus. Hence, there was a need for a description of the thalamus in a wallaby. This study describes the organisation and the cyto-architectonics of the thalamus of the tammar, Macropus eugenii. Except for the midline nuclei, the boundaries of all other nuclei are well demarcated due to their well-differentiated nuclear components. Within the lateral posterior complex, a pulvinar nucleus was identified, and the pre-tectal nuclei show extensive differentiation, as do the medial geniculate nuclei. Also, a small centre-median nucleus was identified. The anteroventral nucleus retains its dorsal position for its entire rostrocaudal extent. The nucleus of the optic tract is located in a dorsal position in the tammar, as it is in cats. The general conclusion from this study is that the nuclear organisation of the thalamus in the tammar, a metatherian mammal, is complex and comparable in most respects to that in cats, eutherian mammals.