Archives of Medical Research 36 (2005) 436–440 ORIGINAL ARTICLE Formation of the Cochlear Nerve in the Modiolus of the Guinea Pig and Human Cochleae Mu ¨rvet Tuncel, a H. Selc ¸uk Su ¨ru ¨cu ¨, a K. Mine Erbil a and Ali Konan b a Department of Anatomy, b Department of Surgery, Hacettepe University, Faculty of Medicine, Ankara, Turkey Received for publication November 3, 2004; accepted February 2, 2005 (D-04-00136). Background. Central processes of the bipolar neurons in the spiral ganglion converge in the modiolus to form the initial portion of the auditory branch (cochlear nerve) of the eighth cranial nerve. This occurs before the cochlear nerve passes through the internal auditory meatus. The neurons of the spiral ganglion send their central processes towards the internal acoustic meatus, through a single canal to form the cochlear nerve. These processes are described in many textbooks as running through numerous longitudinal small canals called canales longitudinales modioli before entering the internal acoustic meatus. Results of this study indicated that the term; “canalis longitudinalis modioli” was considered to be more appropriate than the former. Methods. Central processes of the bipolar neurons in the spiral ganglion of the guinea pig and human cochleae were investigated using stereo, light and electron microscopy. Results. Detailed examination of the guinea pig and human cochleae by light, electron and stereomicroscopy did not reveal multiple longitudinal canals but a single canal for the cochlear nerve. Conclusions. The singular term canalis longitudinalis modioli is more appropriate than canales longitudinales modioli.  2005 IMSS. Published by Elsevier Inc. Key Words: Cochlea, Modiolus, Cochlear nerve, Guinea pig, Human, Microscope. Introduction The modiolus is a spongy bony axis. Blood vessels and nerves are located within this structure. The spiral osseous lamina extends from the modiolus in a shelf-like manner. The spiral canal of modiolus is located where the spiral osseous lamina joins the modiolus. The spiral ganglion is located within this canal. The central processes of the bipolar neurons forming this ganglion constitute the cochlear nerve. Initial portion of the cochlear nerve in the modiolus was described with the name canales longutidunales modioli or not mentioned in a number of textbooks, papers and also in Terminologia Anatomica–1998 (1–12). Although a few studies on the human cochlea were performed, the similarity Address reprint requests to: Mu ¨rvet Tuncel, M.D., Hacettepe University, Faculty of Medicine, Department of Anatomy, 06100, Ankara, Turkey. Phone: (+90) 312-305-21-18; FAX: (+90) 312-310-71-69; E-mail: mtuncel@hacettepe.edu.tr 0188-4409/05 $–see front matter. Copyright  2005 IMSS. Published by Elsevier Inc. doi: 10.1016/j.arcmed.2005.02.003 between the guinea pig and the human cochlea was accepted by most of the investigators. In this study, the modiolar course of the cochlear nerve was examined in guinea pig cochleae and the human cochleae obtained from preserved cadavers. Materials and Methods The guinea pig and human cochleae were prepared for light and electron microscopy and the human cochleae were also observed and photographed under the stereomicroscope. Guinea pig. Five guinea pigs were anesthetized with ether and sacrificed by decapitation. Temporal bone was removed and a window of 1.5–2 mm was opened from the bulla for better diffusion of the chemicals used for the processing of the tissues (anterior wall). Each temporal bone was fixed immediately with 10% formalin for 24 h for light microscopic examination. They were decalcified with 5% nitric acid for 6 h, washed with