Red-tailed Phascogale brain — Comparative Brain Anatomy

**Red-tailed phascogale (Phascogale calura) Dasyuridae**

The brain of the red-tailed phascogale

The endocranial volume of the red-tailed phascogale is just under a ml (mean + SD for 5 specimens of 0.91 + 0.16 ml) and the brain is approximately 16 mm in length, making the brain slightly larger than that of a domestic mouse.

The cerebral cortex is smooth with only an alpha sulcus and a rhinal fissure visible. The olfactory and entorhinal regions are proportionally large so the rhinal fissure courses along the lateral margin of the cerebral hemisphere and even appears in the superior view at the edge of the hemisphere.

Common features of the cerebral hemispheres of all small dasyurids include the large areal size of S1 and V1, with the caudolateral extension of the former. All small dasyurids have a similar proportional area occupied by hippocampal formation (Phascogale calura – 25.5% of total pallial area), olfactory (piriform) cortex (Phascogale calura – 15.8% of total pallial area) and isocortex (Phascogale calura – 58.7% of total pallial area). Within the isocortex (6-layered cortex), S1 and V1 occupy 7.8 and 8.7% of total pallial area, respectively. The proportional area of primary auditory cortex is much lower – only 1.5%, suggesting that olfaction, vision and trigeminal somatosensation (from facial whiskers) are the dominant senses in these small carnivores.

The superior and inferior colliculi are exposed and the cerebellum is smooth, with small cerebellar hemispheres and paraflocculi, and no primary cerebellar fissure visible to the naked eye.

References

Ashwell KW, McAllan BM, Mai JK, Paxinos G (2008) Cortical cyto- and chemoarchitecture in three small Australian marsupial carnivores: Sminthopsis macroura, Antechinus stuartii and Phascogale calura. Brain Behavior and Evolution 72, 215-232.

Fig. 1 Superior view of the brain of the red-tailed phascogale.  The cerebral hemispheres are smooth except for an alpha sulcus near the olfactory bulb and the rhinal fissure (rf) which runs around the lateral margin of the hemisphere and … — Fig. 1 Superior view of the brain of the red-tailed phascogale. The cerebral hemispheres are smooth except for an alpha sulcus near the olfactory bulb and the rhinal fissure (rf) which runs around the lateral margin of the hemisphere and swings superiorly at the caudal pole. The superior and inferior colliculi are exposed. The primary sensory areas (S1, V1, Au1) are deduced from cytoarchitectural features (see Ashwell et al., 2008).

Fig. 2 Inferior view of the brain of the red-tailed phascogale.  Most of the inferior cortical surface is taken up by primary olfactory (piriform) cortex and the entorhinal cortex. The trigeminal nerves are large, reflecting a behavioural reliance on trigeminal somatosensation from the facial hairs. — Fig. 2 Inferior view of the brain of the red-tailed phascogale. Most of the inferior cortical surface is taken up by primary olfactory (piriform) cortex and the entorhinal cortex. The trigeminal nerves are large, reflecting a behavioural reliance on trigeminal somatosensation from the facial hairs.

Fig. 3 Unfolded cortical map showing the relative sizes of identified cortical areas in the pallium (cortex) of the brain of the red-tailed phascogale.  The map is modified from data collected for Ashwell et al. (2008). — Fig. 3 Unfolded cortical map showing the relative sizes of identified cortical areas in the pallium (cortex) of the brain of the red-tailed phascogale. The map is modified from data collected for Ashwell et al. (2008).