The proOtic encloses between it and the lateral occipital the fenestra ovalis, into which fits the columella of the ear.
16), extending between the fenestra ovalis and the tympanic membrane or drum, consists of (I) the long and slen der columella, a straight, ossified rod which fits with a disk into the fenestra r; t st ovalis; it is homologous with the stapes (m.st.), although not stirrupshaped; (2) the extra-columellar mass.
Monodonta, no jaws, spire not prominent, no umbilicus, columella toothed.
mc, Columella muscle (muscular process grasping the shell).