Creation of an MRI-Based Three-Dimensional Common Wombat (Vombatus ursinus) Brain Atlas and Linking Brain Morphometry to Wombat Behaviour.

Marsupials lack a corpus callosum; in its place Diprodontia have a fasciculus aberrans connecting the hemispheres. However, despite this uniqueness, the realm of marsupial brain anatomy remains largely unexplored, especially through the lens of modern imaging techniques. Currently, there is a glaring absence of publicly available reference materials to explore normal brain morphometry to aid in defining and investigating marsupial neurodegenerative brain diseases. This study segmented magnetic resonance images of a wombat brain with an overall size of 41,745.46 mm3 to create a three-dimensional atlas. The volume and ratio to the overall brain size of each segment were quantified. The common wombat has a moderate hippocampal formation (2464.34 mm3; 5.90%), thick hippocampal commissure (535.19 mm3; 1.28%), well-developed tectum (481.42 mm3; 1.15% and a large epithalamus; 53.96 mm3; 0.13%). The common wombat's moderately sized cerebellum (5181.99 mm3; 12.41%) with prominent folia and fissures but less folding may suggest the low need for complex motor movement when burrowing. The common wombat also has a large diencephalon (3104.70 mm3; 7.44%), large thalamus (2206.81 mm3; 5.29%), a moderately sized hypothalamus (530.71 mm3; 1.27%), moderately sized basal ganglia (caudoputamen) (1345.26 mm3; 3.22%) and moderately sized pons and medulla (2475.26 mm3; 5.93%).