ИСТИНА

The intracranial fissure serves hares to suppress masticatory noise, not to save the eyes as suggested by Bramble in 1989. Alexander N. Kuznetsov1*, Alexander N. Oshkin2 1 Faculty of Mechanical Engineering, Technion, Haifa, Israel; 2 Faculty of Geology, Moscow State University, Moscow, Russia. * Email: sasakuzn@gmail.com Leporids differ from all other mammals by the presence of an intracranial fissure. It traverses the skull from the interparietal-supraoccipital suture at the top, between squamosal and petrotympanic laterally, and between basisphenoid and basioccipital at the bottom. It cuts the skull into ethmoid-orbit-mandibular and otic-occipital moieties, separating the jaw joint from the inner ear. We propose that it disrupts the bone conduction of the owner's masticatory noise to cochlea, thus enhancing the ability to discriminate the sound of an approaching predator during chewing. To check this hypothesis we used a fresh head of an adult Lepus europaeus. The skin was cut along the top of the skull, and flat areas were made on bones with a file for metal, to which a pair of piezoelectric transducers was glued with cyanoacrylate. One was constantly glued to parietal, and the second was glued to frontal, supraoccipital or mastoid. The masticatory sound was produced by hand-driven side-to-side movement of mandibular against maxillar teeth. RMS amplitudes of wavelets were compared on the two channels of oscilloscope. The mean parietal-to-frontal RMS amplitude decrease, characterizing the masticatory noise attenuation within the orbit-mandibular moiety, was about 2.2-fold. The attenuation across the fissure was considerably larger. The mean parietal-to-supraoccipital attenuation was about 2.9-fold, and the parietal-to-mastoid one was about 6.7-fold. Thus, the mastoid, representing the nearest place to the cochlea, was proved to be the most silent area in the head in respect of the masticatory noise. Further experiments are required to prove the suggested hypothesis. Keywords: cochlea, inner ear; jaw joint; Lepus europaeus; piezoelectric transducer; sound conduction.