Avian fissura prima: differential accumulation of extracellular matrix at a fold.

Extracellular matrix components that flank the fissura prima, a primary surface infolding of the cerebellum in birds and mammals, were examined in the embryonic chick using light and transmission electron microscopy. Cerebella dissected from Day 10 embryos were perfused with a paraformaldehyde-glutaraldehyde-tannic acid primary fixative and sectioned in the sagittal plane through the mid-vermis. Ultrastructural analysis revealed a distinct, continuous basal lamina separating the organ parenchyma (epithelia) from pia mater (mesenchyme) at the fissure surface (arbitrarily labeled; fissure floor, folia wall, and folia apex).