We used the same neuromeric criteria as those applied to describe the early neuromeric TH-IR neurons in human embryos (Puelles and Verney, 1998). According to the models described in Lumsden (1990), Krumlauf (1994), Rubenstein et al. (1994), Puelles (1995), and Guthrie (1996) (see also Material and Methods, Nomenclature), the different neuromeres are individualized by longitudinal and transverse black bars, and the different histogenetic fields are labeled in black capitals. The optic recess is marked with a black circle. In this scheme, the different TH-IR groups are mapped. Groups displaying a transient tyrosine hydroxylase immunoreactivity are labeled with a superscript “t”. Each subgroup was labeled according to its location; for instance, the isthmic component of A10 is labeled A10i where “i” stands for the isthmus, except for the transient TH-IR groups located in the piriform cortex (pir), the anterior amygdala (AA), and the olfactory tubercle (OT), which appear in the intermediate telencephalic territory (ITA), the region from which they are supposed to be derived (Fernandez et al., 1998). TH-IR groups displaying Pax6 immunoreactivity appear in boxed black italics. A1–A17, Catecholaminergic groups; AB, anterobasal nuclei; ACB, nucleus accumbens; ACX, archicortex; AEP, entopeduncular area; AH, anterior hypothalamus; AP, alar plate; BP, basal plate; BST, bed nucleus of stria terminalis; C1–C3, putative adrenergic groups; CB, cerebellar primordium; CGEL, caudal ganglionic eminence, lateral part; CGEM, caudal ganglionic eminence, medial part; DMH, dorsal medial hypothalamic nucleus; DT, dorsal thalamus; ET, epithalamus; FP, floor plate; HCC, hypothalamic cell cord; IC, inferior colliculus; Is, isthmus; LGE, lateral ganglionic eminence; LL, lateral lemniscus; MA, mammillary region; mes, mesencephalon; MGE, medial ganglionic eminence; OB, olfactory bulb; p1–p6, prosomeres; PC, posterior commissure; PAVH, paraventricular hypothalamic nucleus; PEP, posterior entopeduncular area; PF, prechordal floor plate; POA, anterior preoptic area; POP, posterior preoptic area; PP, prechordal plate; PTECT, pretectum; r1–r8, rhombomeres; RCH, retrochiasmatic nucleus; RP, roof plate; SCH, suprachiasmatic nucleus; SPV, supraoptic/paraventricular region; EMT, thalamic eminence; TECT, midbrain tectum; TU, tuberal hypothalamic region; VT, ventral thalamus.