The term brain (BRN) refers to one of two parts of the central nervous system (CNS) as defined by dissection in vertebrates ( Swanson-2015 ).. It is the part of the CNS located in the cranial cavity (CCV); the other is the spinal cord (SPC) ( Carpenter-1983 ). The vertebrate BRN consists of three parts: forebrain (FBR), midbrain (MBR) and hindbrain (HBR). Some biologists also use 'brain' in reference to the central ganglion of the nervous system (NS) of invertebrate species ( Wikipedia ). Neuroscientists have created a number of comprehensive hierarchical Model of BRN topology and internal structure in sufficient detail to be used for quantitative analyses of BRN structure and function ( Bowden-1997 ). Most published since the 1970s are stereotaxic atlases that meet criteria for use in quantitative neuroanatomy, namely, the entire brain is included and all structures are defined by boundaries such that every point in the BRN appears in one and only one primary structure ( Bowden-1997 ). Three basic kinds of hierarchical Model are functional, structural and developmental. Functional Model are most useful for correlating brain structure with mental and behavioral functions. The most comprehensive is a neurobehavioral state Model: the Functional CNS Model - Rat ( Swanson-2004 ). In structural Model, primary structures are grouped by proximity, a format that is most useful in targeting structures for implanting electrodes, chemtrodes and other devices, or for surgical intervention. See, for example, Structural CNS Model - Macaque based on the primate brain hierarchy of Bowden-1995 and Martin-2000 and updated in this version of NeuroNames. A comprehensive Developmental Model, in which structures are grouped by the location of their precursor structures (prosomeres) in the embryo together with corresponding gene expression is found in Watson-2017. Updated 29 Oct 2025. .