MORPHOLOGY OF STRUCTURES AND MECHANICS OF SOUND TRANSMISSION IN MIDDLE EAR OF GULLS OF THE GENUS LARUS

The morphology of the sound-transmitting system in the common gull (Larus canus) and the black-headed gull (L. ridibundes) was studied. The morphometric parameters of the tympanic membrane, columella auris and middle ear's ligaments and muscle are given. Based on the morphofunctional comparison of the structures in the colummelian complex in gulls and crows (Corvidae), a similar movement mechanics in the tympanic membrane and the columella auris with the participation of the middle-ear muscle in this process was revealed. Optimization of the sound perception due to the participation of the middle-ear muscle in gulls was confirmed taking into account the morphological adaptations observed and the results of the biomechanical experiment. A scheme for the transversal-forward mechanics of movements with some elements of the columella auris's rotation is suggested. This scheme shows directions of the displacement of the eardrum's surface, the chondral (cartilaginous) and bony parts of the columella auris when the tendon of the midlle-ear muscle in gulls is taut. The vibrational lever-type process of the perception and transmission of acoustic signals in the middle ear was shown to predominate in gulls as well as in crows.