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The purpose of this investigation is to determine, by experimental degeneration methods, point to point afferent neuronal connections between the organ of Corti and the primary cochlear nuclei of the pigeon, and to clarify the central termination of the closely associated nerve from the macula lagenae.At the present time, fundamental problems concerning audition i n m a n and higher mammals are being attacked by electrophysiological experimentation on lower forms. This approach should consider comparative anatomical data, some of which this study is intended to provide. Furthermore, a detailed anatomical knowledge of the more simply constructed avian auditory mechanism is necessary to provide a better understanding of the evolution of the auditory system and to serve as a basis for future morphological and physiological investigation. MATERIALS AND METHODSLesions were placed at selected levels in the cochlear nerve and ganglion of 13 adult domestic pigeons ranging i n weight from 240 to 400 gms. The birds were initially anesthetized by intramuscular injections of Veterinary Nembutal (20 mg/kg of body weight) and maintained under surgical anesthesia by the periodic administration of ether.A lateral operative approach was used to place lesions in the proximal half of the cochlear nerve and ganglion. Muscle and spongy bone were removed until the round window was exposed. The proximal half of the cochlear nerve was then exposed by removing the secondary tympanic membrane covering the round window. Such an exposure made it possible, with the visual aid of a Zeiss operating microscope, to interrupt the cochlear nerve partially or completely as desired.Placement of lesions in the distal half of the cochlear nerve required a ventral approach through the skull. The floor of the brain case was exposed by retracting the trachea and esophagus, and the spongy bone sheltering the distal half of the cochlea, including the lagena, was picked away.The cochlear nerve was transected at various levels by cutting with iridectomy scissors or disrupted by carefully squeezing with Swiss watchmakers forceps. More discrete lesions were made in the cochlear nerve or ganglion with small straight or hooked needles or with a n electrosurgical needle.The placement of lesions i n this manner made i t possible to confine them to the cochlear portion of the labyrinth and thus spare vestibuIar fibers and ganglion cells located next to the medulla. In no case did the experimental animals exhibit vestibular disturbances during the post-operative period.Two to three days following operations, the animals were anesthetized, and perfused after the method of Koenig, Groat and Windle ('45). Following removal of the calvarium, the heads were immersed in 10% neutral formalin. The following day the brain and auditory capsules were removed and further fixed and hardened in 10% neutral formalin for a week or longer.1This investigation was carried out during the tenure of a postdoctoral fellowship (no.

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