Fig. 1

Evolution of the hypothalamic ventricles in bony vertebrates. Schematic drawing of embryonic (a) and adult (b) brains of rodent, frog, zebrafish, and Polypterus is shown above a phylogenetic tree of the Osteichthyes (bony vertebrates). a Horizontal view of embryonic brains through the anterior forebrain, highlighting the morphological diversity of the hypothalamic recesses (ventricular zones are shown in black). The horizontal section level (red line) is displayed in the top left panel (dotted square) with in a schematic embryonic brain. b Sagittal sections of adult brains. The inferior lobe (IL) is a brain structure present in teleosts but not in tetrapods or in Polypterus. The asterisks indicate hypophysis in each animal. Abbreviations: 3 V third ventricle, F forebrain, H hindbrain, IL inferior lobe, LR lateral recess, M midbrain, PR posterior recess