Anteroposterior axis ( Swanson & Bota, 2010 ) : Often used as synonym for rostrocaudal axis in most vertebrates and for the dorsoventral axis in humans; see Standring (2008, Fig. 1). Application of this old and confusing designation is discouraged; see anterior (Aristotle) and anterior (Galen, c177). Also spelled anterior-posterior axis.

Architecture ( Swanson & Bota, 2010 ) : The conceptual structure and overall logical organization of a system-here the nervous system (Monro, 1783)-from the point of view of its function or design; see Oxford English Dictionary (1989) and Sherrington (1906, pp. 271, 308).

Closed chain ( Swanson & Bota, 2010 ) : A series of connections in a topological circle; that is, one can start at any node and follow connections back to the same node; synonyms include circuit, loop, and cycle.

Connections ( Swanson & Bota, 2010 ) : The total input-output relationships of a node or set of nodes, in contrast to an individual connection.

Foundational Model of Connectivity ( FMC ; Bota & Swanson, 2010 ) : Abbreviated form of "Foundational Model of Structural Connectivity in the Nervous System". The term is derived from Foundational Model of Anatomy (FMA); see Brinkley (1991).

Origin ( Swanson & Bota, 2010 ) : The neuron (Waldeyer, 1891), neuron type (Bota & Swanson, 2007), or gray matter region that generates a connection or output; see Herrick (1915, p. 108).

Partial correspondence ( Swanson & Bota, 2010 ) : In neuroanatomy many terms do not fit exactly into any part of the structural hierarchy. Such terms partly correspond to a standard term somewhere in the hierarchy, and should be defined (described) with reference to the immediately higher standard term within which it completely fits. The concept of a partly corresponding term is important because such a term generally does not share all of the properties of any particular reference term and thus cannot fit exactly anywhere within the hierarchy as such-it does not have a strict PART-OF relationship with any component of the Foundational Model of Connectivity hierarchy. This is because gray matter regions and neuron types (Bota & Swanson, 2007) generally are not homogeneous; instead, they have defining and differentiable features in parameter space that occur in gradients. As a result different sites within a gray matter region generally have different features and thus different microconnections.

Peripheral ganglia ( GPR ; Swanson & Bota, 2010 ) : A peripheral ganglion is a macroscopic aggregation of neurons (Waldeyer, (1891), that is, a gray matter region, in the peripheral nervous system (Meckel, 1817) of invertebrates and vertebrates; see Bullock & Horridge (1965, p. 51), also see ganglion (Galen, c173).

Peripheral nerve cord ( Swanson & Bota, 2010 ) : A topographic division that has a longitudinal peripheral nerve cord trunk (equivalent to a white matter tract) with a series of more or less regularly spaced peripheral ganglia along its course, and a trunk segment between two adjacent ganglia called a peripheral longitudinal communicating branch. The prototypical vertebrate example is the sympathetic trunk (Winslow, 1733) with its sympathetic trunk ganglia (Winslow, 1733)-together the sympathetic cord.

Subsystems microarchitecture of nervous system ( Swanson & Bota (2010) ) : One of two common orthogonal ways to describe completely the nervous system (Monro, 1873). Subsystems here deal with the accurate microscopic (histological) delineation and description of gray matter regions and white matter tracts, in contrast to the topographic description of nervous system that deals with macroscopic locations in the nervous system. For the nervous system (Monro, 1783), connections and the routes they take are described in terms of gray matter regions and white matter tracts, which are formed by neuron types (Bota & Swanson, 2007), neuron parts, and molecules. An individual nervous system subsystem is a set of connections that form a complex unity with a specific function; also see systems description of body.

Supporting structures of nervous system ( Swanson & Bota, 2010 ) : Topographic macrostructure features that include the connective tissue coverings of the nervous system (Monro, 17893)-the meninges (Edwin Smith Surgical Papyrus, c1700 BC)-and the compartment within and surrounding the nervous system that is filled with cerebrospinal fluid (CSF; in ventricles-subarachnoid space); see Millen & Woollam (1962). It is important to consider that the circulatory system pervades the nervous system.

Supraesophageal ganglion ( Swanson & Bota, 2010 ) : Invertebrate brain that lies dorsal (Barclay, 1803) to the digestive system in annelids and arthropods. One or more supraesophageal ganglia may be involved, depending on how many central nerve cords there are in a species; see Bullock & Horridge (1965, pp. 662, 1609), Reisinger (1972), and ventral ganglia.

Synonym ( Swanson & Bota, 2010 ) : The semantic relationship between a standard term and a synonym is an identical definition, and for relevant Foundational Model of Connectivity terms implies identical connections.

Systems description of body ( Swanson & Bota, 2010 ) : One of two common orthogonal ways of describing completely the body; the other is the topographic description of body. An individual body system is a set of interconnected or interdependent parts that form a complex unity with a specific function; see Dorland's (2003), Oxford English Dictionary (1989). A set of body systems together describes completely the structure-function organization of the body; see Brash (1951, p. 4), Hollinshead (1974, pp. v-vii), Williams (1995, pp. 2, 15). Also called a systematic description of body.

Terminal autonomic nerves ( TAN ; Swanson & Bota, 2000 ) : A topographic division of autonomic nerves (Langley, 1898) that macroscopically appear to arise mostly from terminal ganglia (Gaskell, 1886) and/or terminal plexuses; nicely illustrated for macrodissected adult humans by Ranson (1920, Fig. 250).

Terminal plexuses ( TPL ; Swanson & Bota, 2010 ) : A topographic division of autonomic nerves (Langley, 1898) that form more or less discrete anastomoses of small white matter tracts (bundles) in or near the walls of innervated viscera. They are characterized by parasympathetic ganglion cells that only sometimes condense into macroscopically obvious terminal ganglia (Gaskell, 1886). The distinction between terminal plexuses and prevertebral plexuses is clearly illustrated by Ranson (1920, Fig. 250) and Williams & Warwick (1980, Fig. 7-224, and pp. 1122-1137).

Terminal-of-passage ( Swanson & Bota, 2010 ) : A terminal (Cajal, 1899) on a very short stalk that protrudes from an axon trunk or axon collateral (Cajal, 1899) along its course rather than at the terminal arborization (Cajal, 1888) of the trunk or collateral. With the light microscope they resemble dendritic spines. See Fox & Barnard (1957, Fig. 9), Gerfen & Sawchenko (1984, pp. 231, 235, Fig. 10-F).

Termination ( Swanson & Bota, 2010 ) : The neuron (Waldeyer, 1891), neuron type (Bota & Swanson, 2007), or gray matter region where a connection or output ends; see Herrick (1915, p. 108).

Topographic arrangement of gray matter regions ( Swanson & Bota, 2010 ) : A hierarchical arrangement of gray matter regions based strictly on a particular scheme of topographic divisions, including topographic divisions of cerebrospinal axis.Swanson (1992, Table A) provided a systematic example for the 10 elementary topographic divisions of cerebrospinal axis of the adult rat.

Topographic description of body ( Swanson & Bota, 2010 ) : One of two common orthogonal ways of describing completely the body; the other is the systems description of body. Topography here deals with the accurate geometric delineation and description of locations in the body; see Oxford English Dictionary (1989). For mammals the major locations are head, neck, trunk, and extremities. A hierarchical set of topographic locations together describes completely the body from a structural perspective; see Brash (1951, p. 3), Hollinshead (1974, pp. v-vii), Williams (1995, pp. 2, 15).

Topographic division ( Swanson & Bota, 2010 ) : A macrostructural part of the nervous system (Monro, 1783) created at least conceptually by cutting (dividing) with a knife between defined structural landmarks and fitting into a recognized macrostructural hierarchy; see Swanson (2000). The central nervous system (Meckel, 1817) and peripheral nervous system (Meckel, 1817) are the two major topographic divisions, except in animals with just a nerve net, which has divisionless topography.

Topographic divisions of cerebrospinal axis ( Swanson & Bota, 2010 ) : Since Classical Antiquity at least six fundamentally different ways to divide the cerebrospinal axis (Meckel, 1817) have been used, although today there is rather broad consensus about a set of major topographic divisions. The set of divisions is arranged in a hierarchical parceling scheme that is based primarily on structural differentiation of the neural tube (Baer, 1837) and its end product in adult macrostructure or gross anatomy (Swanson, 2000). There are 10 elementary divisions at the bottom: cerebral cortex (Bauhin, 1605), cerebral nuclei (Swanson, 2000), thalamus (His, 1893a), hypothalamus (Kuhlenbeck, 1927), tectum (Schwalbe, 1891), tegmentum (Swanson, 2000), cerebellum (Aristotle), pons (Haller, 1747), medulla (Winslow, 1733), and spinal cord (Galen, c162-c166). There is considerably more controversy about smaller topographic divisions below the level of the ten elementary divisions. The 17 terms in the hierarchy below cerebrospinal axis (Meckel, 1817) are very useful "building blocks" that may be combined in many ways to create new terms, like brainstem, which can have different meanings depending on which elementary divisions are included (Swanson, 2000, Tab. 1).

Topographic macroarchitecture of nervous system ( Swanson & Bota, 2010 ) : One of two common orthogonal ways to describe completely the nervous system (Monro, 1783). Topography here deals with the accurate macroscopic (gross anatomical) delineation and description of major locations in the nervous system, in contrast to the subsystems description of nervous system that deals with the microscopic-histological organization of gray matter regions and white matter tracts-and the connections they form. A topographic location in the nervous system, like the midbrain (Baer, 1837), is usually a heterogeneous mixture of components, including parts of the circulatory system, meninges (Edwin Smith Surgical Papyrus, c1700 BC), ventricles-subarachnoid space, gray matter regions, and white matter tracts.

Transverse tract ( Swanson & Bota, 2010 ) : A white matter tract coursing essentially along the transverse axis (Henle, 1855) of the nervous system (Monro, 1783); if a transverse tract crosses the median plane (Henle, 1855) in an animal with bilateral symmetry, the segment related to that plane is a commissure. The basically transverse and longitudinal organization of nervous system tracts was emphasized early on by Spencer (1881) and Cajal (1899-1904, vol. 1, p. 12), and more recently in the orthogon theory of Reisinger (1925, 1972).

Vascular cells ( Swanson & Bota, 2010 ) : They form the blood vessels and blood cells within them and are part of the circulatory system; see Peters et al. (1991, Ch. 10).

Ventral ganglia ( Swanson & Bota, 2010 ) : The invertebrate central ganglia lying caudal (Cleland, 1879) to the supraesophageal ganglion and ventral (Schulze, 1893) to the digestive system on a central nerve cord trunk; the central ganglia and central nerve cord trunk together form a central nerve cord. See Bullock & Horridge (1965, p. 662).

Ventricular system ( VS ; Swanson & Bota, 2010 ) : Synonym for ventricles (Hippocrates).

Ventricular-subarachnoid space ( VSS ; Swanson & Bota, 2010 ) : The continuous cavity associated with the vertebrate central nervous system (Meckel, 1817) that is filled with cerebrospinal fluid (CSF). Part of the cavity is the central lumen of the vertebrate central nervous system (Meckel, 1817) that is the remnant of the embryonic lumen of the neural tube (Baer, 1837); it is referred to as the (cerebral) ventricles (Hippocrates), with walls formed by a monolayer of ependymal cells, a type of glia (Virchow, 1846). The other part is the subarachnoid space (Magendie, 1827) that lies between the outer and inner layers of meninges (Edwin Smith Surgical Papyrus, c1700 BC), the dura (Galen, c177) and pia (Galen, c192), respectively. The ventricles and subarachnoid space are continuous through holes in the roof of the fourth ventricle (Galen, c177) associated with the medulla (Winslow, 1733). The CSF is equivalent to lymph for the central nervous system and eventually drains into the venous part of the circulatory system; see Crosby et al. (1962, pp. 568-579).

White matter tract ( Swanson & Bota, 2010 ) : A recognizable division of white matter (Meckel, 1817) in the nervous system (Monro, 1783) that can be bordered by gray matter (Meckel, 1817), another white matter tract(s), or non-neural tissue. Borders between white matter tracts are determined by defined structural landmarks and are commonly arbitrary. White matter tracts may be homogenous or heterogeneous. A homogeneous tract only has one specific mesoconnection (Thompson & Swanson, 2010) within it, whereas a heterogeneous tract has two or more specific mesoconnections within it. The traditional way to view vertebrate white matter tracts is with a myelin stain, supplemented with a reduced silver stain (Brodal, 1981, p. 5). There are many general terms for a white matter tract; some examples include pathway, bundle, fascicle, funiculus, column, peduncle, decussation, commissure, and nerve, whereas others have specific names like corpus callosum, fornix, and internal capsule. As a complete set, white matter tracts can be arranged in various ways, for example, strictly topographically into transverse tracts, longitudinal tracts, and local tracts. White matter tracts were distinguished in the second century by Galen (c177; see translation by Singer, 1999, pp. 231, 234) for macrodissected nonhuman mammals, and were referred to as tracts as long ago as Willis (1664; see translation by Pordage, 1681, pp. 61, 91) for macrodissected adult humans and other large mammals.

Wiring diagram ( Swanson & Bota, 2010 ) : An illustration of the physical arrangement of connections (including route information) between a set of nodes-gray matter regions, neuron types (Bota & Swanson, 2007), or neurons (Waldeyer, 1891)-in the nervous system (Monro, 1783). Wiring diagrams can be at various levels of abstraction from three-dimensional models to two-dimensional schema but a complete wiring diagram, by definition, includes route information; see Gregory (1966), Wikipedia (Wiring diagram).