Phylogenetic Development and Gross Anatomy of the Pineal Complex
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Development and gross anatomy of the pineal complex have been repeatedly and comprehensively dealt with (Studnicka 1905; Bargmann 1943; Vollrath 1981; Korf and Oksche 1986; Korf 1994); thus this chapter reviews only some basic facts (Fig. 2). The pineal develops from a circumscribed area of the diencephalic roof between the habenular and posterior commissures. Interestingly, the other key components of the photoneuroendocrine system, the retina and the suprachiasmatic nucleus, are also derivatives of the diencephalon. With a few exceptions (e.g., hagfish, crocodiles), a pineal complex is present in all vertebrates investigated thus far. In many species whose pineal complex is endowed with functional photoreceptor cells the tissues overlying the pineal region display peculiar specializations; the most pronounced is the parietal foramen of the skull, which is already present in fossils, suggesting the existence of a pineal complex in Silurian and Devonian vertebrates, the ancestors of recent fish, amphibians, and lacertilians. In several recent vertebrates the pineal complex is divided into two distinct components.
KeywordsPineal Region Posterior Commissure Pineal Organ Frontal Organ Habenular Nucleus
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