Exostoses and cavernous venous formation in the external auditory canal ofthe hooded seal as a functional physiological organ

Exostoses of the external auditory canal (EAC) develop after protracted mec hanical, chemical or thermal irritation in particular. This is a common dis order among aquatic sportsmen and has been considered unique to Man. We dis sected and photodocumented the EACs of 5 newborn and 3 adult Hooded Seals ( Cystophora eristata). Serial sections of the EACs were prepared for light m icroscopic evaluation after staining with haematosylin-eosin or toluidine b lue. All EACs exhibited a firm, broad-based. mountain peak-shaped exostosis on the floor of the meatus, lateral to the eardrum. In addition, the meata l skin of the bun) EAC harboured large venous sinuses. The exostosis and ve nous sinuses of the seal EAC participate in the protection of the sensitive hearing apparatus, particularly the pars tensa portion of the drum, during diving.