The NeuroLex Mammalian Brain is a work in progress (8 August, 2010) by the International Neuroinformatics Coordinating Facility (INCF). Scheduled for completion in September, 2010 this model will be a hierarchical representation of brain structures believed to be present in most mammals based on their presence in brain of the primate (human and macaque) and the rodent (rat and mouse). Structures in the model are defined by a combination of topology (location and shape) and internal structure (architecture as revealed by stains for Nissl-substance and myelin). They are grouped on the basis of proximity. The model was generated from the NeuroNames Classical Primate Brain ( Bowden-1995 ) by: 1) substitution of the architectonic parcellation of cerebral cortex ( Stephan-1975 ) for the topological, sulcus-based, parcellation of the Classical Primate Brain; 2) elimination of subdivisions of structures whose components differ across species; 3) elimination of surface features, such as sulci, tubercles and cranial nerves. Upper levels of the subcortical hierarchy are organized according to the Encephalon division of the Nomina Anatomica (Nomina-1983) with extension to lower levels based on a number of standard textbooks, brain atlases and research publications ( Bowden-1995; Bowden-1997, Bowden-2005 ).