Afterbrain ( Baer, 1837 ) : Synonym for medulla (Winslow, 1733); term introduced for vertebrates by Baer (1837, p. 107, in the original German, "Nachhirn"). Also see His (1895, p. 162).

Forebrain ( Baer, 1837 ) : Synonym for adult vertebrate endbrain (Kuhlenbeck, 1927); in the original German, "Vorderhirn"; p. 107. For later use see Ariëns Kappers (1929, Figs. 44, 45), Papez (1929, Ch. 40).

Hindbrain ( HB ; Baer, 1837 ) : Rostral (Schulze, 1893) half of the primary hindbrain vesicle (Baer, 1837) of the vertebrate neural tube (Baer, 1837) as it develops into the adult cerebellum (Aristotle), which lies dorsally (Barclay, 1803), combined with the pons (Haller, 1747), which lies ventrally (Schulze, 1893); p. 107, in the original German, "hinterhirn". The term for this topographic division has been used in this sense more recently, for example by His (1895, p. 162), Obersteiner & Hill (1900, p. 46). The term is derived from the fact that since the time of Aristotle and Galen the cerebellum, often combined with the pons, was routinely considered the posterior brain, hindbrain, or small brain, whereas in contrast the cerebrum was often considered the anterior brain, forebrain, or large brain; see Swanson (2000). Synonyms include epencephalon (Sharpey et al., 1867), secondary hindbrain (Sharpey et al., 1867), metencephalon (Huxley, 1871).

Interbrain ( IB ; Baer, 1837 ) : The caudal (Cleland, 1879) and ventral (Schulze, 1893) topographic division of the forebrain (Goette, 1873); the rostral (Schulze, 1893) and dorsal (Barclay, 1803) division is the endbrain (Kuhlenbeck, 1927). The interbrain in turn has two great topographic divisions, dorsally (Barclay, 1803) the thalamus (His, 1893a) and ventrally (Schulze, 1893) the hypothalamus (Kuhlenbeck, 1927). This basic division of the macrodissected adult human brain (Edwin Smith Surgical Papyrus, c1700 BC) has been recognized at least since Varolio (1573, p. 13, his "pars posterior medullae spinalis"), and it received its current name for vertebrates from Baer (1837, p. 107; in the original German, "Zwischenhirn"). This English form of diencephalon (Sharpey et al., 1867) has been used routinely, for example by Sharpey et al. (1867, p. 577), Johnston (1906, p. 25), Strong & Elwyn (1943, p. 12), and Williams & Warwick (1980, p. 953).

Midbrain ( MB ; Baer, 1837 ) : The middle of the three primary brain vesicles of the vertebrate neural tube (Baer, 1837) that develops into the adult midbrain (Baer, 1837), a topographic division between forebrain (Goette, 1873) and rhombicbrain (His, 1893b). Malpighi (1675; see translation by Adelmann, 1966, p. 1003) identified the cristate vesicle in the chick neural tube, and Baer named it the midbrain vesicle for embryonic vertebrates (1837, p. 106; in the original German, "mittlere Hirnbläachen"). Baer also named the corresponding adult structure the midbrain (1837, p. 107; in the original German, "Mittelhirn"). A synonym is the Latin mesencephalon (Sharpey et al., 1867).

Neural tube ( NT ; Baer, 1837 ) : The embryonic primordium of the adult cerebrospinal axis (Meckel, 1817) that is formed from the neural plate (Stricker, 1860) by the process of neurulation; see Nieuwenhuys et al. (2008, pp. 7-9). Galen probably glimpsed the macrodissected mammalian neural tube (see Adelmann, 1966, p. 747) and Baer (1837, p. 59) introduced the term for macrodissected vertebrate embryos. Varolio (1573, see English translation, 1969, p. 34) observed three transparent globules (tres globulos transparentes in Latin) in the 9-day macrodissected chick embryo and Baer (1837, pp. 106, 107) called them the three primary brain vesicles (primären Hirnbläschen in German and Vesiculae cerebrales in Latin): anterior or forebrain primary vesicle (vordere Bläschen in German), middle or midbrain primary vesicle (mittleres Bläschen in German), and posterior or hindbrain primary vesicle (hinteres Bläschen in German). He also observed that they develop into 5 vesicles going on to form the 5 morphological elements or basic parts of the adult vertebrate brain (Cuvier, 1800): Vorderhirn, Zwischenhirn, Mittelhirn, Hinterhirn, and Nachhirn in the original German. Sharpey et al. (1867, p. 577) gave the English and Latin equivalents of these 5 parts: secondary forebrain or prosencephalon, interbrain or diencephalon, midbrain or mesencephalon, secondary hindbrain or epencephalon, and afterbrain or metencephalon. In the Foundational Model of Connectivity these 5 parts are called endbrain (Kuhlenbeck, 1927) or telencephalon (Kuhlenbeck, 1927), interbrain (Baer, 1837) or diencephalon (Sharpey et al., 1867), midbrain (Baer, 1837) or mesencephalon (Sharpey et al., 1867), hindbrain (Baer, 1837) or epencephalon (Sharpey et al., 1867), and afterbrain (Sharpey et al., 1967), metencephalon (Sharpey et al., 1867) or medulla (Winslow, 1733). The hindbrain (Baer, 1837) consists of cerebellum (Aristotle) and pons (Haller, 1747).