Figure 1. Preparation of brain sections.

(A) A zebra finch brain after perfusion and extraction from skull. When the fissure is aligned along the 60° red line, cutting the brain horizontally gives rise to the transverse or Frankfurt plane. (B) The brain is oriented according to the fissure between the tectum and forebrain. (C) Digital photograph of a frozen block face during sectioning in the sagittal plane. (D) The block face of a frozen brain sectioned in the transverse plane. Both images (C) and (D) are digitally enhanced to exhibit coarse-scale structures and provide references suitable for 3D serial reconstruction. For anatomical abbreviations, see list.