Hindbrain ( Galen, c192 ) : Synonym for cerebellum (Aristotle); see translation by Duckworth (1962, p. 18).

Pia ( PI ; Galen, c192 ) : The innermost of the meninges (Edwin Smith Surgical Papyrus, c1700 BC), closely covering the brain (Edwin Smith Surgical Papyrus, c1700 BC) and spinal cord (Galen, c162-c166) and consisting of reticular, elastic, and collagenous fibers. It is histologically similar to the arachnoid (Blasius, 1666), and the two are often considered together as the leptomeninges; see Dorland's (2003), Standring (2008, p. 389). The pia was apparently known to Hippocrates in Places in Man (see translation by Potter, 1955, p. 23) and was described and named such by Galen (c192; see translation by Duckworth, 1962, p. 6).

Plexus ( plx ; Galen, c192 ) : A general term for a group of interconnecting neurons (Waldeyer, 1891) or nerve (Herophilus, c335-280 BC) components that may be a sheet of interwoven fibers or a course mesh of communicating nerves, without or with neuron cell bodies (Deiters, 1865), including ganglia (Galen, c173); see Oxford English Dictionary, 1989; Bullock & Horridge, 1965, p. 1606). Examples include nerve nets, prevertebral plexuses, and spinal nerve plexuses (with postplexus spinal nerves distal to them). Galen (c192; see translation by Duckworth, 1962, p. 243) used the term plexus in describing the macrodissected adult mammalian brachial plexus (Camper, 1760).

Spinal nerve plexuses ( plxs ; Galen (c192) ) : A network of communicating branches (Winslow, 1733) between three or more spinal nerves (Camper, 1760); examples are the cervical plexus (Molinetti, 1675), brachial plexus (Camper, 1760), lumbar plexus (Vesalius, 1543), and sacral plexus (Vesalius, 1543). These plexuses (Galen, c192) were identified in macrodissected adult animals except humans in the second century by Galen; see translations of Duckworth (1962, pp. 230-264) and May (1968, pp. 598-603).

Spinal nerve primary branches ( spb ; Galen (c192) ) : In general, each spinal nerve trunk divides distally into a spinal nerve dorsal branch (Meckel, 1817) and a spinal nerve ventral branch; this arrangement was identified in macrodissected adult animals except humans in the second century by Galen; see translations by Duckworth (1962, p. 229 ff.) and May (1968, pp. 597-599); for contemporary terminology see Durward (1951, p. 1052 and Fig. 913).