THE ANATOMY OF THE COCHLEAR NUCLEI AND SUPERIOR OLIVARY COMPLEX OF ARBOREAL AUSTRALIAN MARSUPIALS

Cytoarchitectural and morphometric analyses were carried out on the co chlear nuclear and superior olivary complexes of nine representative p ossums and gliders, members of a large group of nocturnal, arboreal Au stralian marsupials, many of which have well developed vocalizations. The cochlear nuclear complex was displaced medial to the restiform bod y in all species; this has previously been reported in other marsupial s. The dorsal cochlear nucleus was generally very much larger than any other nucleus in this complex. A small cochlear nerve root nucleus wa s present in all species, a feature shared with rodents, The anteroven tral cochlear nucleus was present throughout almost the entire rostroc audal extent of the complex. The component nuclei of the superior oliv ary complex had similar positional relationships to those in eutherian s. The lateral superior olive was the largest nucleus, having a volume usually greater than the sum of the volumes of the medial superior ol ive and medial nucleus of the trapezoid body. The smaller species had a very much larger number of neurons in the superior olive relative to brain size than did the larger species. A similar disproportion was d emonstrated between cochlear nucleus volume and brain weight.