Bone base of the hearing organ of the Baikal seal in postnatal ontogenesis

The aim of this study was to identify the anatomical features in the structure of the bone base of the auditory analyzer in the Baikal seal. It was found that the parietal, temporal bones, auditory ossicles and bony labyrinth have features both in the structure of the bones and in their connection: in newborns, the bones are connected by syndesmosis, in immature and sexually mature animals, the parietal and squama of the temporal bone are connected by synostosis (projection of the external auditory canal), the petrous bone of the temporal bone (includes the middle and inner ear) is connected synostoseally with the squama of the temporal bone and the basisphenoid of the sphenoid bones, and by syndesmosis with the lateral part of the occipital bone and the lacerated opening. The mastoid part of the petrous bone is expressed and is not covered by other bones as in terrestrial predators, it has a cavity in the form of a cave, which opens on the rocky part with a large opening. The tympanic part is represented by a voluminous tympanic bulla with openings located on it - for the carotid canal, for the bony external auditory canal, for the exit of the facial nerve, for the bony auditory tube. On the dorsal wall are found the cape, the vestibule window, the cochlear window, the opening for the facial nerve, the bony ridge of the carotid canal, the bony opening of the external auditory canal, along the edge of which is the internal bony ring, and, finally, the groove of the bony auditory tube. The rocky part facing the brain cavity also has openings: the entrance to the mammillary cave, the internal auditory canal, the exit of the carotid canal and the entrance to the cochlear aqueduct. The auditory ossicles have specific anatomical features expressed in the long handle of the malleus, the large incus, the oval shape of the lenticular bone and the small stapes. The bony labyrinth is represented by the semicircular canals, the cochlea and the vestibule. It is noted that with age, morphometric parameters undergo minor changes. The anterior and posterior semicircular canals have a common pedicle; ampullae are found only in the anterior and lateral semicircular canals. The vestibule is extensive. The cochlea is disc-shaped; its base turn is located at the cape and is distant from the axis.