Ventromedial view of the left tympanoperiotic complex from a Pacific White-sided Dolphin (<i>Lagenorhynchus obliquidens</i>).

The tympanic bulla has been removed for easy viewing of the structures within the tympanic cavity. Structures are as follows: (A) Sigmoid process (the inside of a hollow tube); (B) Anterior (gracile) process of malleus; (C) Thinnest bony window of the medial sulcus of mallear ridge; (D) Keel of the medial sulcus of mallear ridge; (E) Thin window of the medial sulcus of mallear ridge; (F) Accessory ossicle (processus tubarius); (G) Desiccated portion of fibrous venous plexus; (H) Pars cochlearis; (I) Stapes; (J and K) Anterior ligament of the malleus; (L) Stapedial muscle; (M) Incus; (N) Tympanic ligament (homologous to the ancient tympanic membrane) where it attaches to the sigmoid process, a portion of the tympanic ring; (O) Round window (wherever possible the terminology follows Mead and Fordyce [37]).