Marginal Wood Fern – Dryopteris marginalis

The auditory pit, also known as the otic pit, is the first rudiment of the internal ear. It appears shortly after that of the eye, in the form of a patch of thickened ectoderm, the auditory plate, over the region of the hind-brain. The auditory plate becomes depressed and converted into the auditory pit (or otic pit^[1]).

References

This article incorporates text in the public domain from page 1029 of the 20th edition of Gray's Anatomy (1918)