AbstractThe intrinsic organization of the central nucleus of the inferior colliculus has been studied in the adult cat by means of the Golgi and Nauta techniques. On the basis of cytoarchitecture and fiber connections, the central nucleus can be divided into: (i) a smaller,dorsomedial divisionconsisting mainly of large cells and receiving fibers from the auditory cortex, lateral lemniscus and probably the central nucleus of the other side; (ii) a larger,ventrolateral divisionconsisting mainly of medium and small cells but with some intermingled larger types. This part receives fibers from the lateral lemniscus only.The ventrolateral division has a pronounced laminar arrangement of cells, dendrites and axons. The laminae, although overlapping extensively, form an onion‐like series of concentric, curved shells, most of which are incomplete except for those closest to the center of curvature in the dorsolateral part of the nucleus. It is probable that these laminae provide a basis for the pronounced tonotopic organization of neurons in the nucleus. The thickness of the laminae is determined by the dendritic ramifications of two principal cell types which are fusiform or bi‐tufted. Other, multipolar and large cells have dendrites which lie across one or several laminae and may form a basis for interaction between laminae.Four axon types can be distinguished:Type I(lateral lemniscal) andtype II(corticofugal) axons run parallel to the laminae but in opposite directions, though type II axons are confined to the parts of the laminae projecting into the large‐celled, dorsomedial division.Type IIIaxons are widely ramifying and may arise within the central nucleus or be another form of afferent fiber. Type I and III axons end in dense clusters of terminals on principal cells but as singleen passantterminals on multipolar cells.Type IVaxons are the efferents of the inferior colliculus and run a recurrent course through the central nucleus giving off collaterals which sometimes end on the parent