Brain Gross Anatomy and Cerebellar Histology of the Cattle Egret (Bubulcus ibis)

Abstract

The structural parts of brain are similar in all vertebrates, but they differ in their complexity and organization. The avian brain for instance, is organised differently compared to mammals, with variations existing in the relative size and location of their structures. The cattle egret (Bubulcus ibis) is a cosmopolitan avian species native to Africa. Despite their economic importance as excellent sentinels in assessing environmental pollutants, there is a dearth of information on their neuroanatomy. Hence, we here investigated their gross morphological features and morphometric parameters, and the cerebellar histology. Twelve transcardi-ally perfused juvenile cattle egrets were studied, with the body and brain weights and brain linear measurements considered. The brain weight constituted 0.46 % of the total body mass, with a strong positive correlation recorded between the body and brain weights (r = 0.9204). Morphologically, the brain was lissencephalic, with the corpus callosum absent and the olfactory bulbs rudimentary with no discernible division into the olfactory bulb, olfactory tract and olfactory lobe. We observed prominent sagittal eminence and vallecula telencephali, as well as an obvious fovea limbica on the dorsal and lateral surfaces of the cerebral hemispheres, respectively. The diencephalic structures were completely covered by telencephalon, with the pineal gland occupying the polygonal space between cerebrum, optic lobe and cerebellum. The mesencephalic tectum appeared as a large oval bilaterally bulging structure with prominent optic tracts and constituted the bulk of the midbrain. There was a dorsal extension of the fourth ventricle into the cerebellum known as the ventriculus cerebelli and the cerebellar histology presented a persistent external granular layering suggestive of a potential for adult neurogenesis. Our data has added relevant literature on the cattle egret brain and could prove useful in comparative, developmental and evolutionary avian neuroanatomy.