lateral fold n.
Any of the ventral foldings of the lateral margins of the embryonic disk that establish the definitive embryonic body form.
This lateral fold encloses the flank of the abdomen and is covered with fine oblique and parallel nervures.
All species have numerous papillae in the lateral fold; the fewest lateral papillae are found in S. cyanosticta and phaeota.
From this he derives additional evidence in favor of the origin of paired fins from a lateral fold.