Fig. 3. The anatomy of the crayfish brain and its internal subdivisions. (A) 3D model of the crayfish brain (white) shown inside the exoskeleton (made transparent on the right) in a frontal view. Optic nerves (ON) that project into the eyestalks (Est) and the optic ganglia, lamina (La) and medullae (Me; consisting of medulla externa, medulla interna and medulla terminalis) within the eyestalks, are shown. Antennular (AntN) and antennal (AnN) nerves that project into the bases of the antennules (Ant) and antennae (An), respectively, are also displayed. Ro, rostrum. Scale bar, 4 mm. Inset: Red box indicates the area displayed beneath in the enlargement. (B) The brain and nerves shown without the exoskeleton. Scale bar, 3 mm. (C) Enlargement of the deuto- and tritocerebrum. Identified and displayed structures are the olfactory (OL) and accessory (AL) lobes, the antennal neuropils (AnP), a large artery (Ar), several prominent cell clusters (6, 10, 17) and the esophageal connectives (EC). Scale bar, 1 mm. Data in A–C were reconstructed from images acquired from the same crayfish (mass 37.9 g) that had been injected with 100 µl/120 mmol l^–1 MnCl₂ prior to scanning at T_R=1.5 s, T_E=17.6 ms; matrix dimensions: 512x512, field of view=3.5 cmx3.5 cm, number of averages=96, slice thickness, 250 µm; voxel size, 68x68x250 µm; acquisition time (total), 20.5 h.