The cochlear nuclei of lizards

Abstract

The cochlear nuclei of 14 lizard species (eight families) were studied in normal animals and in a small series of animals with lesions of the posterior division of the eight nerve. The development of the cochlear nuclei is division of the eighth nerve. The development of the cochlear nuclei is directly related to the length and complexity of the papilla basilaris. The best development of basilar papillae and cochlear nuclei is found in teiid and gekkonid lezards, and an intermediate grade of development in scincid, lacertid, and anguid lizards. A lesser degree of development occurs in the iguanids, and practically no cochlear nuclei differentiation is observed in Chameleo. Two well defined cochlear nuclei are found in most lizard families: nucleus angularis (NA) AND nucleus magnocellularis medialis (NMM). NA is located in the cephalic third of the acoustic tubercle and contains variably sized darkly staining cells. NMM is the most caudally located nuclear group and is characterized by regularly round to ovoid cells. The development of NMM is more closely related to papilla basilaaris length and complexity than is NA. Two less well defined cochlear nuclei are also thought to be present. In the region beteen NA and NMM is a sparsely cell-populated area, nucleus magno-cellularis lateralis (NML), which consits of a variety of small, darkly staining cells and large, pale staining cells which are usually laterally located in the nucleus. Like NMM, Nml is better developed in lizards ith more complex papillae basilares. Nucleus laminaris may be represented by a few fusiform cells in the ventral portion of the NML region.