part of part of organ part radio-ulna sulcus longitudinalis In a fused radio-ulna, longitudinal furrow that demarcates the area of fusion of both elements. This sulcus is deep in the distal portion of the compound bone, but barely evident or absent at the proximal end. This class was sourced from an external ontology (amphibian_anatomy). Its definitions, naming conventions and relationships may need to be checked for compatibility with uberon UBERON:3000844