The middle ear of Baikal seal (Pusa sibirica Gmelin, 1788)

Abstract

The research purpose is to study the structure of the middle ear of the Baikal seal. It consists of an eardrum and auditory ossicles located in the tympanic cavity. The Baikal seal has a triangular-shaped drum bubble. At the top of the tympanic cavity, the Eustachian tube is located. Another feature of the tympanic cavity is a bone roller of the carotid artery which has not been found in other seals. Passing through the roller, the carotid artery does not enter the tympanic cavity. There are differences in the structure of the auditory ossicles: on the external surface of the malleus head, there is a recess; the joint between the malleus head and the anvil is quite mobile, which makes it easy to separate the auditory ossicles; the stirrup is light and of a triangular shape; legs of the stapes differ in thickness; the lenticular bone which serves as a joint between the long leg of the anvil and the stirrup, is well seen. At the lateral side of the bony cape, there is an oval vestibule window closed by the stirrups. The cochlea window is covered with an internal mucous membrane of the tympanic cavity and its own membrane.