In olden days they were mostly simple and in modern times, particularly since the middle of the Edo period, carving was done on the inside of the frog's legs and some are made to protrude.
古くはシンプルなものが多く、近世、特に江戸中期以降では股の内側に彫刻を施すことがあり、時に、はみ出して造られたものもある。