only in taxon composed primarily of Chordata neural nucleus Proposed CUMBO def from MM: A subcortical part of the nervous system consisting of a relatively compact group of cells that is distinguishable histologically that share a commonality of cytoarchitecture, chemoarchitecturel and connectivity. (comments: I put in 'subcortical' because I don't think we consider either the cerebellar cortex or cerebral cortex to be nuclei. Some people distinguish between a nucleus and a laminar structure (see Wikipedia definition). However, there are structures identified as nuclei that are laminar, e.g., lateral geniculate nucleus, although they are not laminated in all species. Also, I put in 'relatively compact' and 'distiguishable by histology' because we have groups of cells, e.g., cholinergic cell groups, doparminergic cell groups that are related on the 3 criteria but which we don't tend to consider nuclei because they don't occupy an easily defined territory. But all is open to debate. gray matter central nervous system cell part cluster