Fate-mapping studies in amphibian, chick and mouse embryos (Eagleson et al., 1986; 1995; Couly and Le Douarin, 1985; Cobos et al., 2001; Osumi-Yamachita et al., 1994; Kawamura et al., 2002) have shown that the cells contributing to the adenohypophysis develop at the midline of the anterior neural ridge, which delineates the rostral boundary of the neural plate, a region devoid of neural crest. The anterior neural ridge also gives rise to the olfactory placodes and some forebrain tissues including the olfactory bulbs (reviewed in Papalopulu, 1995). Ablation of this region in chick embryos at the 2-4 somite stage confirmed these lineage analyses as it prevented formation of Rathke's pouch and any further pituitary development (elAmraoui and Dubois, 1993). Upon head folding, the oral ectoderm cells of the adenohypophyseal placode invaginate towards the prospective ventral diencephalon to form Rathke's pouch, the anlage of the adenohypophysis. Rathke's pouch starts as an invagination of the oral ectoderm in response to inductive signals from the prospective diencephalon. The region of the diencephalon above the pouch is known as the infundibulum and forms the posterior lobe of the pituitary or neurohypohysis (Figure 3). While in most basal fish and tetrapods the adenohypophyseal anlagen invaginates to form Rathke's pouch, in teleost fish the adenohypophyseal placode does not invaginate but rather maintains its initial organization forming a solid structure in the head (reviewed in Pogoda and Hammerschmidt; 2009)

consider adding more detailed spatial placement - e.g. oral ectoderm and/or rostal ectoderm

pituitary placode

uberon

UBERON:0009122