Tympanic part of the temporal bone upper part of the posterior wall by the squama. Its inner end is closed, by the tympanic membrane which originates from the tympanic sulcus; the upper limit of its outer orifice is formed by the posterior root of the zygomatic process, immediately below which there is sometimes seen a small spine, the "suprameatal spine", situated at the upper and posterior part of the orifice. The auditory bulla (pl. bullae) is a hollow bony structure on the ventral, posterior portion of the skull that encloses parts of the middle and inner ear. In most species, it is formed by the tympanic
Serous membrane Serous membrane In anatomy, serous membrane (or serosa) is a smooth tissue membrane consisting of two layers of mesothelium, which secrete serous fluid. The inner layer that covers organs (viscera) in body cavities is called the visceral membrane. A second layer of epithelial cells of the serous membrane, called the parietal layer, lines the body wall. Between the two layers is a potential space, mostly empty except for a few milliliters of lubricating serous fluid that is secreted by the two serous membranes. The Latin anatomical name is "tunica serosa". Serous membranes line and enclose several body cavities, known as